The research, conducted by a team at Mashhad University of Medical Sciences in Iran and published in the journal Molecular Biology Reports, examined bone marrow samples from 40 children who had been newly diagnosed with acute myeloid leukemia, one of the most aggressive cancers of the blood and bone marrow. The investigators compared the expression levels of two genes, BMAL1 and WEE1, against samples from 20 non-malignant control subjects. BMAL1, also known by its alternate name ARNTL, is widely regarded as the engine of the molecular circadian clock, forming a transcriptional complex that drives rhythmic gene expression throughout the body. WEE1, by contrast, is a kinase that acts as a gatekeeper at the G2/M checkpoint of the cell cycle, holding cells back from entering mitosis when their DNA is damaged or replication is incomplete.

The results were unambiguous. Using real-time quantitative PCR to measure messenger RNA levels, the team found that both genes were expressed at significantly lower levels in the leukemic samples than in the healthy controls, with statistical significance reaching a P value of less than 0.001. The magnitude of the difference was substantial: relative expression of BMAL1 in the patients’ bone marrow was just 0.18-fold that of the control group, while WEE1 expression stood at 0.31-fold. In other words, the core clock gene had been reduced to less than a fifth of its normal activity, and the cell cycle checkpoint kinase to less than a third.

Perhaps the most intriguing finding emerged when the researchers looked at how gene expression related to clinical measurements. BMAL1 expression showed a significant negative correlation with both white blood cell count and blast percentage, the proportion of immature, leukemic cells in the bone marrow. The correlation coefficients were -0.440 for white blood cell count, with a P value of 0.004, and -0.418 for blast percentage, with a P value of 0.007. This means that the more aggressive the disease appeared by standard hematological measures, the more profoundly the circadian clock gene was suppressed. WEE1 expression, in contrast, showed no significant correlation with any of the hematological parameters evaluated, including white blood cell count, hemoglobin, platelet count, and blast percentage.

To understand why these findings matter, it helps to appreciate how deeply the circadian clock and the cell cycle are intertwined. The clock operates through a transcription-translation feedback loop: BMAL1 pairs with CLOCK to activate expression of Period and Cryptochrome genes, whose protein products later feed back to inhibit BMAL1-CLOCK activity, creating an oscillation with a period of roughly 24 hours. Crucially, many of the genes controlled by this loop are involved in cell division. Landmark work published in Science in 2003 showed that the clock directly times cell division in vivo, and subsequent studies demonstrated that BMAL1 regulates the expression of p21, a key inhibitor of cell proliferation. When BMAL1 activity collapses, this timing coordination is lost, and cells may divide without the temporal safeguards that normally restrain them.

WEE1 sits at the intersection of this crosstalk. The kinase phosphorylates and inhibits CDK1, the master driver of mitotic entry, thereby enforcing the G2/M checkpoint that gives cells time to repair DNA damage before dividing. Loss of WEE1 function is known to produce genomic instability, and experiments in mice have shown that WEE1 deficiency leads to hyperactivation of the APC/C complex, chromosomal abnormalities, and ultimately carcinogenesis. At the same time, WEE1 has become a major target in cancer drug development, because many tumors become dependent on WEE1-mediated checkpoint control to survive the DNA damage inflicted by chemotherapy. WEE1 inhibitors are currently being explored in clinical trials across a range of malignancies, and prior work has suggested that WEE1 and PARP-1 play critical roles in the treatment of myelodysplastic syndrome and acute myeloid leukemia.

The downregulation of both genes in pediatric AML therefore paints a coherent, if preliminary, mechanistic picture. A silenced BMAL1 could mean that the leukemic cells have lost clock-driven control of proliferation and DNA damage responses, while reduced WEE1 might reflect a breakdown of checkpoint integrity that allows genetically damaged cells to progress through the cycle. It is worth noting, however, that the relationship between BMAL1 and cancer is not simple. Some studies have found that BMAL1 can actually accelerate certain tumors; one 2023 investigation reported that the clock protein promotes acute myeloid leukemia progression by inhibiting ferroptosis, a form of regulated cell death, through the EBF3/ALOX15 axis. In other cancers, including pancreatic, colorectal, and tongue squamous cell carcinoma, BMAL1 appears to act as a tumor suppressor, and its loss promotes growth and drug resistance. The new pediatric AML data, showing that lower BMAL1 tracks with higher tumor burden, leans toward the tumor-suppressive interpretation in this context, but the authors are careful to frame the finding as suggestive of a role rather than proof of one.

The study also fits into a broader literature on clock gene disruption in blood cancers. Researchers have previously documented downregulation of circadian genes in chronic myeloid leukemia, where altered methylation patterns of the PER3 gene have been observed, and in chronic lymphocytic leukemia, where both clock genes and clock-controlled cell cycle genes show deregulated expression. More recently, the circadian clock circuitry has been shown to modulate the activity of leukemia-initiating cells in T-cell acute lymphoblastic leukemia, and BMAL1 and CLOCK expression patterns have been examined as potential diagnostic markers in multiple myeloma. Animal work adds further weight to the connection: disrupting the light-dark cycle in mice has been shown to impair the hematopoietic function of the bone marrow, the very tissue from which leukemia arises.

For clinicians and researchers, the immediate value of the study lies in its potential biomarker implications. Because BMAL1 expression correlated inversely with white blood cell count and blast percentage, it is conceivable that measuring clock gene activity could eventually help gauge disease burden or track response to therapy in pediatric AML, a disease in which risk stratification remains a major clinical challenge. The authors also point toward therapeutic possibilities, noting that the significant downregulation of BMAL1 and WEE1 suggests that disrupted circadian and cell cycle regulatory pathways may contribute to the pathogenesis of the disease. The emerging field of chronotherapy, which seeks to time drug administration to the patient’s internal rhythms to maximize efficacy and minimize toxicity, could also be informed by a better understanding of how the clock is rewired in leukemic cells.

Significant caveats remain. The study involved a relatively modest sample of 40 patients from a single center, and it measured messenger RNA rather than protein levels, leaving open the question of whether the observed transcriptional changes translate into altered protein function. Correlation does not establish causation, and it is not yet clear whether BMAL1 suppression drives leukemic progression or is merely a consequence of it. The authors note that the data supporting the findings are available from the corresponding author upon reasonable request, and the work was carried out under the ethical oversight of Mashhad University of Medical Sciences with written informed consent from the parents or legal guardians of all pediatric participants. Follow-up studies with larger cohorts, longitudinal sampling, and functional experiments in leukemic cell models will be needed to determine whether restoring clock gene activity could one day form part of a therapeutic strategy. For now, the message is clear and quietly profound: the machinery that tells our cells what time it is may also help decide whether they stay healthy, and in the bone marrow of children with acute myeloid leukemia, that machinery appears to have fallen silent.

Subject of Research: Dysregulation of the circadian clock gene BMAL1 and the cell cycle regulator WEE1 in pediatric acute myeloid leukemia

Article Title: Dysregulation of circadian clock gene BMAL1 and cell cycle regulator WEE1 in pediatric AML

Article References: Oraei Sajjadi, K., Ayatollahi, H., Sheikhi, M., & Ahmadi, M. H. (2026). Dysregulation of circadian clock gene BMAL1 and cell cycle regulator WEE1 in pediatric AML. Molecular Biology Reports, 53(1), Article 1624. https://doi.org/10.1007/s11033-026-12812-9

Image Credits: AI Generated

DOI: 10.1007/s11033-026-12812-9

Keywords: acute myeloid leukemia, BMAL1, WEE1, circadian clock, cell cycle, pediatric cancer, gene expression, bone marrow, G2/M checkpoint, hematologic malignancy, chronotherapy, biomarker

The discovery matters because the evolutionary origin of endogenous, self-sustaining rhythms has long been murky. Complex transcriptional clock networks are well characterized in flowering plants, built from interlocked feedback loops involving genes such as CCA1, LHY, TOC1, GIGANTEA, and the evening complex components ELF3, ELF4, and LUX. But when and how such temporal coordination emerged during the transition from aquatic algae to terrestrial flora has remained an open question. Chara braunii, whose genome was fully sequenced in 2018, occupies a pivotal phylogenetic position near the base of the streptophyte lineage, making it an ideal organism in which to probe the deep history of plant circadian biology.

The research team cultivated Chara braunii from germinated oospores and grew young thalli under a regular 14-hour light, 10-hour dark cycle. Using a custom-built imaging chamber fitted with LED strips and a smartphone camera capturing frames every ten minutes, they tracked the angle between each branchlet and its basal node over three consecutive days. The results were striking: every morning, about an hour after lights came on, the branchlets began to unfurl from a nearly vertical position, opening to angles between 130 and 180 degrees by midday. As evening approached, they folded back toward vertical, settling at angles between 90 and 110 degrees. Statistical analysis with the JTK_CYCLE algorithm confirmed significant rhythmicity with a consistent midday peak, and all eight biological replicates remained significant after correction for multiple testing.

Crucially, the team then transferred the algae to continuous light to see whether the rhythm would persist without any external day-night signal. The answer depended dramatically on brightness. Under continuous regular light of 30 micromoles of photons per square meter per second, the branchlets initially closed, then partially reopened and settled into a stable, semiopen position. No statistically significant circadian oscillation could be detected. But under continuous dim light at half that intensity, the rhythmic opening and closing continued for the full 60-hour recording period, with highly significant periodicity. In other words, the alga’s internal rhythm did not vanish under constant conditions—it was masked or damped by brighter light, a phenomenon also documented in Arabidopsis, where continuous light suppresses rhythmic outputs despite an intact clock.

The researchers propose a plausible physical mechanism for this irradiance effect. Under dim light, a sufficient brightness gradient may persist between the upper and lower sides of each branchlet, maintaining the differential elongation that earlier studies in other Chara species suggested drives bending. Under brighter light, photons may penetrate more effectively through the chloroplast layer, erasing the asymmetry between the two sides of the branchlet. With more uniform illumination, growth becomes more even, and the visible oscillation disappears. The authors caution, however, that branchlet angle is a geometric readout that cannot distinguish growth-driven changes from reversible, turgor-driven movements, and both processes may contribute to the observed rhythm.

The team also examined how the alga acclimates physiologically to continuous illumination. Pigment analysis revealed that chlorophyll a, chlorophyll b, and carotenoid concentrations rose significantly under dim continuous light after 36 hours, consistent with a classic low-light acclimation response that boosts light-harvesting capacity. By 60 hours, absolute pigment levels had declined again, leaving only the chlorophyll a to chlorophyll b ratio elevated. Photosynthetic parameters measured by pulsed-amplitude modulation chlorophyll fluorometry—including maximum electron transport rate, the initial slope of the photosynthesis-irradiance curve, and the light saturation point—showed no detectable temporal variation across days or times of day, suggesting that rhythmic regulation of photosynthesis in this organism, if present, is process-specific rather than global.

Metabolite profiling added another layer of insight. Using liquid chromatography tandem mass spectrometry, the researchers quantified 35 primary metabolites across three sampling points after transfer to continuous light. Under dim light, metabolites related to carbon and nitrogen metabolism accumulated steadily, with malate, fumarate, nicotinate, and glutamate significantly elevated at 36 hours, and malate, fumarate, nicotinate, and alanine remaining high at 60 hours. Under brighter continuous light, changes were smaller and more transient: serine, phenylalanine, and alpha-aminobutyrate rose at 36 hours, while pyruvate declined by 60 hours. The serine increase likely reflects intensified photorespiration, a hallmark of metabolic stress, while the persistent accumulation of TCA-cycle intermediates under dim light suggests enhanced anabolic activity. The divergence between treatments points to an altered carbon-nitrogen balance at higher irradiance and hints that continuous bright light decouples metabolic outputs from temporal control.

Perhaps most intriguingly, a phylogenetic survey of the Chara braunii genome revealed homologs of several major land-plant clock-associated gene families, though with strikingly incomplete conservation. The REVEILLE family is represented by a single protein carrying the characteristic MYB DNA-binding domain but lacking the full architecture of CCA1 or LHY. A putative PRR homolog retains only the CCT domain and cannot be classified as a canonical PRR. GIGANTEA is well conserved in Chara and other late-diverging streptophytes, while the evening complex components ELF3, ELF4, and LUX are all present and broadly conserved. Notably, no canonical ZEITLUPE ortholog with both LOV and Kelch domains was found—only a related ADAGIO-family F-box protein—suggesting that light-input pathways in Chara differ fundamentally from those of flowering plants.

Together, these findings sketch a compelling picture: an endogenous regulatory component capable of driving circadian branchlet movements existed in the streptophyte ancestors of land plants, but its observable output is modulated by light intensity, and its molecular machinery was assembled from parts that only partially overlap with the canonical angiosperm clock. The co-occurrence of attenuated rhythmic movement and a distinct metabolic profile under brighter continuous light provides a framework for future mechanistic work, even though the present data cannot establish a causal link between the two. For evolutionary biologists, the message is tantalizing: the seeds of the plant circadian clock were already sown in aquatic algae, long before the conquest of land, waiting for brighter light—or better experiments—to reveal their full rhythm.

Subject of Research: Circadian regulation of branchlet movement and irradiance-dependent acclimation in the charophyte alga Chara braunii

Article Title: Circadian Oscillations in Branchlet Angle and Irradiance‐Dependent Acclimation in Chara braunii Under Continuous Light

Article References: Maidel, A.-M., Kurtović, K., Heise, C. M., Vosolsobě, S., Petrášek, J., Timm, S., & Schubert, H. (2026). Circadian Oscillations in Branchlet Angle and Irradiance‐Dependent Acclimation in Chara braunii Under Continuous Light. Plant Direct, 10(10), Article e70194. https://doi.org/10.1002/pld3.70194

Image Credits: AI Generated

DOI: 10.1002/pld3.70194

Keywords: Chara braunii, circadian clock, charophyte algae, branchlet movement, continuous light, irradiance acclimation, chlorophyll, metabolomics, streptophyte evolution, plant physiology, circadian rhythm, clock genes

The research, conducted in the fruit fly Drosophila melanogaster, addresses a fundamental gap in neuroscience. The circadian clock does more than govern sleep and wakefulness; it also modulates physiological functions such as body temperature and hormone production across the animal kingdom. Yet identifying the specific neurons that carry the clock’s instructions to downstream brain regions, and understanding the mechanisms by which the clock exerts influence over those circuits, has proven difficult. The Geneva team, led by Emi Nagoshi of the Section of Biology in the university’s Faculty of Science, turned to the fruit fly precisely because its nervous system, while capable of generating complex behaviors, is compact enough to be mapped genetically with precision.

Using genetic mapping of the connections between neurons, the researchers identified the nerve cells that lie directly downstream of the biological clock neurons in the fly brain. This step was crucial, because knowing which cells receive the clock’s output is the prerequisite for understanding how temporal information is converted into neural activity. The team then applied imaging techniques capable of measuring neuronal activity, and these measurements revealed something striking: the activity of the downstream circuit varies throughout the day, rising and falling in step with the fly’s internal rhythm rather than remaining constant.

The connection the researchers uncovered links the clock neurons to a population of neurons that produce dopamine, a chemical messenger that allows neurons to communicate with one another and that is well known for its role in motivation, movement, and arousal across species. In the fly, the dopaminergic neurons identified in this study project to the mushroom body, a brain structure with a distinguished history in neuroscience research. The mushroom body is involved in learning and memory, but it also participates in the regulation of sleep, and its activity contributes to promoting wakefulness during the day.

The circuit operates through a logic of inhibition and release. According to Blanca Lago Solis and Rafael Koch, a postdoctoral researcher and a research associate in Emi Nagoshi’s group, the clock neurons inhibit the dopaminergic neurons, which in turn stimulate neurons in the mushroom body. “We observed that the clock neurons inhibit these dopaminergic neurons, which in turn stimulate neurons in the mushroom body. This brain region plays a role in learning, memory and the regulation of sleep, and its activity contributes to promoting wakefulness during the day,” the researchers explained. When the clock neurons are actively suppressing the dopaminergic cells, the wake-promoting signal to the mushroom body diminishes. When that inhibition is lifted, the dopaminergic neurons fire more strongly, the mushroom body receives a more powerful stimulus, and wakefulness is promoted.

This push-and-pull arrangement gives the biological clock a direct channel through which it can inform a behaviorally relevant brain circuit about the time of day. Rather than the clock issuing a simple on-or-off command, the circuit modulates the strength of a wakefulness signal in a rhythm that tracks the twenty-four-hour cycle. The result is a mechanism by which abstract temporal information, generated by molecular oscillators inside clock neurons, is translated into graded neuronal activity that coordinates a complex behavior: the alternation of sleep and wakefulness across the day.

The study’s findings carry significance beyond the fly brain. Dopamine’s role in promoting wakefulness is a theme that recurs throughout biology, and the Geneva work highlights how central this neurotransmitter is to the interface between circadian timing and behavioral state. By showing that clock neurons regulate dopaminergic signaling to the mushroom body through rhythmic transcription involving the gene Pka-C1, the study, titled Circadian control of dopaminergic signaling to the mushroom body regulates sleep through rhythmic Pka-C1 transcription in Drosophila, demonstrates that the clock’s influence extends deep into the molecular machinery of the circuits it controls, shaping not only which neurons are active but how their chemical messages are delivered.

Why does this matter for human health? Disruptions of the circadian clock are associated with a range of sleep disorders and alterations in brain function. Shift work, jet lag, and irregular light exposure all desynchronize the internal clock from the external world, and the consequences extend from poor sleep to broader impairments in cognition and mood. A better understanding of the fundamental mechanisms by which the clock communicates with arousal circuits could ultimately help explain how disturbances in biological rhythms affect the brain, and may point toward strategies for mitigating those effects.

There is also a methodological lesson in the Geneva team’s approach. By combining genetic mapping of neuronal connections with live measurements of neural activity, the researchers were able to trace a complete pathway from clock to behavior in a way that would be extraordinarily difficult in larger animals. The fruit fly, the small vinegar fly long attracted to ripe fruit in laboratories around the world, once again proves its worth as a model organism: its circadian clock, its dopaminergic neurons, and its mushroom body all have counterparts whose principles illuminate biology far beyond the species in which they were first described.

As research continues, the circuit described by Nagoshi and her colleagues offers a concrete framework for asking the next generation of questions: how other clock outputs reach other brain regions, how the rhythm of dopaminergic signaling is maintained across the day and night, and how similar clock-to-circuit architectures might operate in the mammalian brain. For now, the study stands as a clear demonstration that the biological clock does not merely keep time; it actively transmits that time to the circuits that decide when an animal sleeps and when it wakes, one dopamine signal at a time.

Subject of Research: Circadian clock regulation of dopaminergic signaling and sleep-wake cycles in Drosophila

Article Title: How the biological clock regulates phases of wakefulness

Article References: How the biological clock regulates phases of wakefulness. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: circadian clock, Drosophila melanogaster, dopamine, mushroom body, sleep regulation, wakefulness, neural circuit, University of Geneva, Current Biology, Pka-C1, neuroscience, biological rhythms

The switch is a protein called SLC25A34, a little-studied transporter embedded in the membranes of mitochondria, the power plants inside fat cells. Researchers at the university’s Novo Nordisk Foundation Center for Basic Metabolic Research, known as CBMR, found that this single protein is tuned simultaneously by three forces: the time of day, the ambient temperature, and what the animal eats. In doing so, it connects the body’s 24-hour clock to the fat cell’s decisions about storing and spending energy. According to corresponding author Associate Professor Zach Gerhart-Hines, the finding challenges the conventional view that these are separate systems. A mitochondrial transporter that responds to clock, cold, and diet, he notes, raises the possibility of therapies that shift when and how the body burns fuel, a fundamentally different lever from today’s obesity and diabetes treatments.

The discovery began as a data-mining exercise. The team searched large datasets for proteins in mouse brown fat that respond to both the circadian clock and to cold exposure, hoping to find candidates that might bridge the two signals. Only two proteins passed every test. One was UCP1, the famous uncoupling protein that converts fuel directly into heat and has been the centerpiece of brown fat research for decades. The other was SLC25A34, a related mitochondrial transporter whose function had never been established. Under comfortable warm conditions, brown fat contains less SLC25A34 than almost any other organ in the mouse. But after just 24 hours in the cold, levels of the protein rose an astonishing 90-fold, transforming brown fat into the tissue with the highest abundance of SLC25A34 in the entire body. That dramatic swing suggested the protein plays a central role in the tissue’s adaptive response.

To understand how the gene encoding the protein, Slc25a34, is controlled, the researchers studied mice engineered to lack specific regulatory proteins. What emerged was a remarkably layered control system with three separate inputs, each answering to a different signal. A clock protein called REV-ERBα keeps the gene switched off during sleep and releases the brake before waking, aligning the transporter’s production with the animal’s daily rhythm. Cold exposure lifts that brake at any hour of the day, overriding the circadian schedule whenever extra heat is urgently needed. And fat itself, whether mobilized from the tissue’s own stores or delivered by the diet, switches the gene on through a third protein, PPARα, a well-known sensor of fatty acids. In effect, the gene listens to the clock, the thermostat, and the pantry all at once.

One of the study’s most intriguing findings is a seeming contradiction. Both fasting, which pushes the body to burn fat, and insulin, the hormone that drives fat storage, increase SLC25A34 levels. Signals for burning fat and building fat, two processes usually treated as opposites, converge on the same transporter. The explanation lies in a quirk of brown fat biology: when the tissue is activated, it does not simply burn pre-existing fat. Instead, it actively builds new fat molecules and then burns them in a continuous cycle. This lipid cycling generates heat as a byproduct and, in the process, clears fat and sugar from the bloodstream, which helps explain why active brown fat is associated with better metabolic health. SLC25A34 appears to keep this cycle turning by carrying a molecule called oxaloacetate back into the mitochondria, replenishing a critical intermediate needed to keep fat synthesis running.

The functional importance of the transporter became clear when the researchers removed it. Brown fat cells lacking SLC25A34 burned less fuel, and in living mice the tissue’s fat-burning response was significantly weaker. The team has not yet demonstrated directly that the transporter carries oxaloacetate, nor have they determined what losing it means for long-term health, so important questions remain open. Still, the evidence points to SLC25A34 as a necessary component of the fat-building-and-burning engine that makes brown fat such a powerful metabolic organ. The work also hints at broader roles: the protein is highly expressed in the heart and has been implicated in brain and liver metabolism, though its function in those organs remains a mystery.

Human relevance is suggested by two lines of evidence, both of which come with caveats. In brown fat cells obtained from human donors, silencing the transporter reduced fuel burning in cells from three of four individuals, indicating that the mechanism is not unique to mice. More strikingly, across 24 clinical studies, people with more SLC25A34 in the white fat beneath their skin tended to be leaner and metabolically healthier. The researchers are careful to stress that this is an association, not proof of cause. It is possible that higher levels of the transporter contribute to leanness, or that leaner, healthier people simply express more of it. Distinguishing between these possibilities will require further study, but the correlation adds weight to the idea that this transporter matters for human metabolism.

The implications for medicine are considerable. Current treatments for obesity and diabetes generally aim to reduce energy intake or alter how the body handles glucose and lipids. A therapy that instead shifts when and how the body burns fuel, by modulating a transporter that integrates circadian, thermal, and dietary signals, would operate on an entirely different axis. Timing of energy expenditure, rather than its total amount alone, could become a therapeutic target. The concept resonates with a growing body of research on circadian metabolism, which has shown that the same meal can have different metabolic consequences depending on when it is eaten. A molecular handle on that timing, situated inside the mitochondria of fat cells, offers a concrete biochemical entry point.

Much remains to be learned. The Copenhagen team, working with collaborators at institutions including the University of Southern Denmark, the University of Pennsylvania, Harvard Medical School, the Broad Institute, and many others across Europe and North America, has only begun to map the transporter’s reach. First author Iuliia Karavaeva of CBMR emphasizes that many mitochondrial transporters still have no known function, and that SLC25A34 turned out to be needed both for building fat and for burning it, a dual role nobody expected. As she puts it, researchers are only scratching the surface. Whether the same clock-temperature-diet integration operates in human brown fat, whether the transporter can be safely targeted with drugs, and what it does in the heart, brain, and liver are questions for the next chapter. For now, the study provides a vivid example of how a single, previously overlooked protein can sit at the crossroads of some of biology’s most fundamental rhythms, turning the body’s furnace up, down, and on schedule.

Subject of Research: Mitochondrial transporter SLC25A34 in brown fat links circadian clock, temperature, and diet to lipid cycling

Article Title: A molecular switch syncs fat-burning to the body clock, our diet and the temperature around us

Article References: A molecular switch syncs fat-burning to the body clock, our diet and the temperature around us. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: brown fat, SLC25A34, mitochondria, circadian clock, metabolism, thermogenesis, obesity, diabetes, lipid cycling, UCP1, PPARα, REV-ERBα

Every mammalian cell contains a molecular clock built from interlocking transcription-translation feedback loops. Core activators such as BMAL1 and CLOCK drive the rhythmic expression of thousands of genes, which in turn coordinate time-of-day-dependent processes including glucose handling, lipid oxidation, protein quality control and immune surveillance. When these clocks falter, the consequences are well documented: inflammation, impaired glucose homeostasis and distorted lipid metabolism, all of which are hallmark features of cancer cachexia. Previous work has shown that tumours can remotely rewire circadian programs in the liver, and the Florida group had already demonstrated that pancreatic cancer disrupts circadian gene expression in a limb muscle, the tibialis anterior. What remained unknown was whether the cardiorespiratory muscles, whose wasting is thought to be a key driver of cachexia-related morbidity and mortality, suffer the same fate.

To find out, the researchers used an orthotopic model of pancreatic ductal adenocarcinoma in which aggressive KPC tumour cells are injected directly into the pancreas of mice. Twelve days after inoculation, a time point corresponding precisely to the onset of cachexia, they collected diaphragm and heart tissue every four hours across a full twenty-four-hour cycle in constant darkness, ensuring that any rhythms they detected reflected endogenous clocks rather than external light cues. They then performed bulk RNA sequencing on each sample and applied sophisticated statistical models that treat gene expression as a continuous sinusoidal function over the day, allowing them to identify rhythmically expressed genes and to detect changes in amplitude, phase and basal expression. The design was powered at over ninety-seven percent to detect circadian rhythmicity, lending confidence to the results.

The findings were striking. In healthy mice, the diaphragm showed robust rhythmicity in 308 genes, but in tumour-bearing mice sixty-four percent of those genes lost their daily oscillations entirely. At the same time, 718 genes that were never rhythmic in healthy diaphragm gained rhythmicity in the cancer state, a wholesale remodelling of the tissue’s temporal architecture. Among the genes losing their rhythm were Nrf1, which guards mitochondrial homeostasis; Pik3c3, a key mediator of autophagy; and Fgf1, a positive modulator of glucose disposal. Genes that gained rhythmicity included inflammatory players such as Tlr7, Il18 and Il18r1, alongside troubling time-of-day-dependent losses in Glut4, the major insulin-regulated glucose transporter, and in Tfeb and Psme4, master regulators of the autophagy-lysosome system and proteasomal quality control.

The heart told a partially different story. Of 1274 genes rhythmic in healthy hearts, fifty-six percent lost their oscillations in tumour-bearing animals, while 246 genes gained rhythmicity. Crucially, core clock gene rhythmicity was largely preserved in the heart, with only Per1 showing elevated basal expression, whereas the diaphragm exhibited significant repression of core clock components including Bmal1 itself, the gene whose deletion in muscle is known to cause metabolic reprogramming, weakness and atrophy. Only about ten percent of the rhythmic genes disrupted in the cancerous hearts overlapped with those altered by cardiomyocyte-specific Bmal1 deletion, suggesting that factors extrinsic to the cardiac clock, such as systemic inflammatory or autonomic signals, are driving much of the disruption.

The temporal coordination of biological processes also collapsed in a tissue-specific manner. In healthy diaphragms, peak expression times of rhythmic genes are spread evenly across the day, reflecting a smooth distribution of daily functions. In cachectic diaphragms, that even distribution vanished, with peak expression re-clustering around the transitions between rest and activity. Genes governing lipid metabolism and amino acid sensing, which normally peak during rest and activity respectively, no longer fired at their proper times. Instead, inflammatory genes and components of ubiquitin-dependent protein breakdown dominated those windows, implying that the muscle’s daily schedule had been hijacked to prioritize immune activation and protein catabolism over metabolic maintenance.

In the heart, the overall distribution of peak expression remained even, but the content of the schedule changed. Genes that regulate heart rate, including Hcn4 and Pde4d, normally peak during the active phase to support the diurnal rise in heart rate and cardiac output driven by sympathetic tone. In tumour-bearing mice, this temporal upregulation was lost, and inflammatory genes such as Il33 and Edn1 peaked during the active phase instead. Phase-stratified analysis revealed that genes involved in adrenergic signalling and contractility, including the beta-1 adrenergic receptor Adrb1, the SERCA2 calcium pump encoded by Atp2a2, and the fatty acid oxidation regulator Ppara, were downregulated in a time-of-day-dependent fashion, while platelet activation genes rose specifically during the active phase, echoing processes implicated in cancer-associated thromboinflammation.

Perhaps the most clinically provocative discovery came from a time-course analysis spanning the entire cachexia trajectory. Drawing on a published RNA-sequencing dataset from diaphragms collected before cachexia, during mild-to-moderate disease and at severe endpoint, the team found that Bmal1 and Clock were significantly repressed by day eight after tumour inoculation, days before any measurable loss of body or muscle mass, and remained suppressed thereafter. The secondary-loop genes Rora and Nr1d1, which encode RORα and REV-ERBα, were also repressed early. Both factors have clock-independent roles in muscle: REV-ERBα promotes mitochondrial biogenesis, represses atrophy genes and is essential for muscle mass maintenance, while RORα regulates lipid homeostasis and protects against pathological fat accumulation. Their early suppression, combined with the fact that both normally restrain NF-κB inflammatory signalling, suggests that clock disruption may precede and actively contribute to diaphragm wasting rather than merely accompanying it.

Why the diaphragm is hit hardest remains an open question, but the authors point to its anatomical proximity to the pancreas, which may expose it to a concentrated bath of tumour-derived factors and a heightened inflammatory microenvironment. Previous work from the same group documented pronounced immune cell infiltration in the diaphragm before cachexia onset, and NF-κB signalling is known to suppress core clock gene expression and interfere with CLOCK:BMAL1 activity. The researchers caution that their study has limitations, including the absence of phenotypic measurements on the same animals used for circadian sequencing and uncertainty about whether the milder cardiac disruption reflects a distinct pathology or simply an earlier stage of a shared trajectory.

The therapeutic implications are considerable. Because the transcriptional damage in these muscles is time-of-day dependent, the findings support testing chronotherapy-based interventions timed to protect muscle mass and function, and they reinforce growing evidence that restoring circadian machinery can halt wasting. Recent work has shown that re-establishing hepatic circadian function in tumour-bearing mice through REV-ERBα overexpression is sufficient to spare both limb muscles and the heart from atrophy, pointing to circadian programs as master regulators of tissue cross-talk during cancer. If similar strategies can be developed for the diaphragm and heart, they could offer a fundamentally new way to defend the muscles that pancreatic cancer patients can least afford to lose.

Subject of Research: Circadian clock disruption in cardiorespiratory muscles during pancreatic cancer cachexia

Article Title: Pancreatic Cancer Disrupts Circadian Patterns of Gene Expression in Cardiorespiratory Muscles

Article References: Ducharme, J. B., Schonk, M. M., Gutierrez‐Monreal, M. A., Ferreira, L. F., Esser, K. A., Judge, A. R., & Judge, S. M. (2026). Pancreatic Cancer Disrupts Circadian Patterns of Gene Expression in Cardiorespiratory Muscles. Journal of Cachexia, Sarcopenia and Muscle, 17(5), Article e70383. https://doi.org/10.1002/jcsm.70383

Image Credits: AI Generated

DOI: 10.1002/jcsm.70383

Keywords: pancreatic cancer, cachexia, circadian clock, diaphragm, heart, gene expression, Bmal1, inflammation, muscle wasting, RNA sequencing, metabolism, chronotherapy

The study, led by Emanuela Talarico and Leonardo Bruno of the University of Calabria, together with Fabrizio Araniti of the University of Milan and colleagues, focused on a special mutant line of the model plant Arabidopsis thaliana. This line, called drm1 drm2 cmt3, or simply ddc, carries disruptions in three genes that encode the enzymes responsible for establishing and maintaining non-CG DNA methylation. Unlike the better-known CG methylation that silences genes symmetrically across both DNA strands, non-CG methylation occurs in CHG and CHH sequence contexts, where H stands for any base other than guanine. In plants, this form of methylation is guided by small interfering RNAs and is intimately tied to the defense of the genome against transposable elements, but its role in shaping normal developmental responses has remained far less clear.

To probe that role, the researchers grew both the ddc mutant and wild-type seedlings under a range of light conditions, varying not just the presence or absence of light but also its quality, including the red, far-red, and blue wavelengths that plants perceive through distinct photoreceptor systems. The results were striking in their specificity. Under all light conditions tested, the mutant seedlings displayed a stronger inhibition of hypocotyl elongation than their wild-type counterparts, meaning that losing non-CG methylation made the seedlings hypersensitive to light’s growth-suppressing signal. Yet when the seedlings were grown in complete darkness, the mutant’s elongation capacity was largely preserved. This dissociation is the crux of the finding: the basic cellular machinery for elongation remains intact in the mutant, but the responsiveness to light-mediated inhibitory signals is amplified.

That distinction matters because it reframes how we think about epigenetic regulation of growth. If the ddc mutant had simply been a stunted plant, one might conclude that methylation loss damages growth machinery in a general way. Instead, the data point to a regulatory role: non-CG methylation appears to act as a brake or tuning knob on the light-signaling pathway itself. Remove the methylation, and the brake loosens, allowing photoreceptor-derived signals to push harder on the developmental switch. In the dark, where those signals are absent, the seedling grows essentially as it should. The epigenetic mark, in other words, does not build the engine; it calibrates the accelerator’s sensitivity to the environment.

The photomorphogenic program extends well beyond stem length, and the mutant’s phenotype reflected that breadth. The researchers observed altered cotyledon expansion in the ddc seedlings, suggesting that the opening and greening of the embryonic leaves, a hallmark of the light-grown state, is also tuned by non-CG methylation. Even more intriguingly, stomatal development was perturbed. Stomata, the microscopic pores on the leaf surface that regulate gas exchange and water loss, arise through a precisely orchestrated series of asymmetric and symmetric cell divisions, and light is known to promote their formation through pathways involving peptides such as STOMAGEN and EPFL9. Finding that a methylation-defective line shows altered stomatal patterning implies that epigenetic state influences not just gross organ growth but the fine-grained cell-fate decisions that build a functional leaf surface.

To connect these visible phenotypes to molecular mechanisms, the team performed gene expression analyses on selected markers spanning two key regulatory circuits: the circadian clock and the photosynthesis apparatus. The circadian clock, built around the reciprocal regulation of genes such as CCA1, LHY, and TOC1, is deeply entwined with light signaling, and it in turn gates hypocotyl elongation through a coincidence mechanism that integrates photoperiod with internal time. Photosynthesis-associated genes, meanwhile, represent the downstream output of successful photomorphogenesis, the point at which a seedling converts light energy into chemical fuel. The analyses revealed alterations in the light responsiveness of these clock-related and photosynthesis-associated genes in the ddc mutant, indicating that the loss of non-CG methylation reshapes how the transcriptional network interprets the light signal rather than merely changing one endpoint.

This is not the first hint that methylation and light signaling converse. Previous work has shown that photoreceptors such as cryptochrome 2 and phytochrome B influence chromatin compaction, and that the transcription factor HY5, a central positive regulator of photomorphogenesis, recruits the histone deacetylase HDA15 to repress cell elongation genes. Histone acetylation dynamics have been repeatedly linked to light-regulated transcription, and the Elongator complex has been implicated in hypocotyl growth both in darkness and in the light. Relatedly, a recent study from some of the same Calabria groups demonstrated that non-CG methylation represses the SDC gene to modulate hypocotyl elongation during thermomorphogenesis, the plant’s developmental response to warm temperature. The new findings extend this theme from temperature to light, suggesting that non-CG methylation may be a general-purpose modulator of how environmental signals are translated into growth decisions.

The ddc mutant has also proven to be a rich resource for understanding stress biology. Earlier studies from the same laboratories showed that the hypomethylated line is impaired in auxin signaling, displays curled-leaf phenotypes, and responds differently to cadmium toxicity, with alterations in root stem cell niche maintenance, hormone pathways, and reactive oxygen species homeostasis. Taken together, this body of work paints non-CG methylation as a versatile layer of regulation that touches auxin biology, stress responses, and now photomorphogenesis. What unites these observations is the idea that methylation patterns do not merely lock genes into permanent silencing, as once assumed, but instead provide a dynamic, tunable substrate through which developmental and environmental information can be integrated.

Why would plants evolve such a system? One plausible logic is ecological. A seedling’s light environment is variable and unpredictable, and the appropriate growth response depends on context: how much red versus far-red light is present, whether the seedling is shaded by competitors, and what time of day the light arrives. An epigenetic layer that modulates the gain of the light-signaling pathway could allow a plant lineage to fine-tune its sensitivity to light across generations or in response to the conditions experienced by the mother plant, without altering the underlying DNA sequence. Because non-CG methylation in plants is guided by small RNAs and can be dynamically re-established, it is well suited to play such a regulatory role, sitting at the interface between genome defense, chromatin architecture, and environmental responsiveness.

The implications reach beyond basic biology. Understanding how epigenetic marks tune light responses could inform crop improvement strategies aimed at seedling establishment, shade avoidance, and photosynthetic efficiency, all traits of enormous agricultural significance. If breeders or genome editors could adjust the methylation state of key light-responsive loci, they might produce seedlings that establish more robustly under variable field lighting or that allocate less biomass to stem elongation in dense canopies. For now, the Calabria team’s results establish the principle: in Arabidopsis, the loss of non-CG DNA methylation enhances a seedling’s sensitivity to light, alters cotyledon and stomatal development, and reshapes the expression of clock and photosynthesis genes. An epigenetic layer, it turns out, helps decide what a seedling sees when it first opens its molecular eyes to the sun.

Subject of Research: The role of non-CG DNA methylation in regulating light-dependent seedling development and photomorphogenesis in Arabidopsis thaliana

Article Title: Loss of non-CG DNA methylation modulates photomorphogenic responses in Arabidopsis thaliana (Brassicaceae)

Article References: Talarico, E., Greco, E., Palermo, A. M., Chiappetta, A., Araniti, F., & Bruno, L. (2026). Loss of non-CG DNA methylation modulates photomorphogenic responses in Arabidopsis thaliana (Brassicaceae). Plant Biosystems, 160(5), Article 272. https://doi.org/10.1007/s44473-026-00285-4

Image Credits: AI Generated

DOI: 10.1007/s44473-026-00285-4

Keywords: DNA methylation, photomorphogenesis, Arabidopsis thaliana, epigenetics, light signaling, hypocotyl elongation, circadian clock, stomatal development, ddc mutant, plant development, chromatin, seedling growth

The research, led by the team of Liu Xiaoqin, combined careful observation of leaf behavior under different lighting regimes, time-series transcriptome profiling across a full day, and a series of molecular assays to connect clock components with downstream transporter genes. The central question was deceptively simple: how do light and clock signals reach the genes responsible for moving water and sugar into and out of the motor cells that power leaf folding? The answer, the researchers propose, runs through a transcriptional network in which the clock protein CCA1 and a pulvinus-enriched MYB transcription factor regulate SWEET sugar transporters and PIP aquaporins, the very proteins that could link timekeeping to turgor pressure changes in the leaf pillow, or pulvinus.

The team began by establishing that peanut leaf movement genuinely depends on the light-dark cycle. Under a normal photoperiod of 16 hours of light and 8 hours of darkness, the leaves closed progressively after the lights went off at 21:30 and were fully closed by 23:00. When the lights came back on at 5:30 the next morning, the leaves gradually unfolded and resumed their stretched daytime posture by around 7:00. Under continuous illumination, however, this characteristic rhythm was suppressed: the leaves remained largely unfolded, showing only slight up-and-down movements. The comparison demonstrated that, in this experimental system, an alternating light-dark cycle is essential for maintaining the visible opening and closing behavior, underscoring the importance of photoperiodic entrainment for nyctinasty.

To trace the temporal signals behind the movement, the researchers sampled plants at 14 time points across the day and analyzed gene expression in both creeping and upright peanut types. Under normal light-dark cycles, the expression patterns followed a clear temporal order. Clock-related genes such as LHY/CCA1 were expressed mainly in the early morning, certain PRR genes peaked in the afternoon, and TOC1 and related genes were active in the evening or at night. When plants were kept under continuous light, the expression fluctuations of some clock genes weakened, yet the overall morning and evening ordering of their expression was largely preserved. This dissociation was informative: visible leaf movement was inhibited by constant light, but the molecular timekeeping apparatus had not simply shut down, suggesting that the photoperiod acts at a level between the clock and the physical movement of the leaves.

With the rhythmic framework in place, the team searched for candidate genes whose expression tracked the light and clock signals. Two functional classes stood out. The first comprised SWEET sugar transporter genes, members of a family that mediates the movement of sugars across membranes and could therefore influence the distribution of carbohydrates between the leaf blade and the pulvinus. The second comprised PIP aquaporin genes, which encode water channels that govern the transmembrane flow of water. Both classes are plausible entry points for connecting time signals to turgor pressure, since leaf opening and closing in legumes depends on rapid, coordinated changes in water content and solute concentration within the pulvinus motor cells. Notably, the candidate genes showed distinct tissue-specific expression patterns: the two PIP genes detected were expressed mainly in the pulvinus region of compound leaves, one MYB transcription factor gene was enriched in the pulvini of both compound leaves and leaflets, and the two SWEET candidates were more inclined toward leaf expression, hinting at collaboration between leaf and pulvinus tissues.

To test whether regulatory relationships actually connect the clock to these transporter genes, the researchers turned to yeast one-hybrid screening and dual-luciferase reporter assays. The yeast one-hybrid analysis identified candidate transcription factors capable of binding the promoters of the transporter genes, and the reporter assays measured the functional consequences of those interactions on promoter activity. The results converged on a specific connection: the clock protein CCA1 was able to recognize evening element (EE) motifs in the promoters of certain SWEET genes and of the pulvinus-enriched MYB transcription factor gene, placing a core circadian component directly upstream of the candidate regulatory network.

The sequence specificity of this binding was verified by electrophoretic mobility shift assays, or EMSA. When CCA1 was added to DNA probes containing intact EE sequences, protein-DNA complexes formed that migrated more slowly through the gel, a hallmark of specific binding. The signal weakened when the EE sequence was mutated, and it was also reduced by the addition of an excess of unlabeled competitive probe, which outcompeted the labeled probe for CCA1 binding. Together, these controls supported the conclusion that CCA1 binds the corresponding promoter fragments in a sequence-specific manner, providing direct molecular evidence that a clock factor is wired into the downstream regulatory network governing leaf movement.

The dual-luciferase reporter assays added a functional dimension to the picture. CCA1 and some of the MYB factors tested were able to enhance the activity of the promoter of a PIP aquaporin gene, indicating that clock and clock-associated transcription factors do not merely occupy these promoters but can actively modulate their output. Taken together with the tissue expression data, the results support a working model in which photoreceptors and the circadian clock coordinate the expression of transporter and regulatory genes: CCA1 and related MYB factors regulate SWEET sugar transporters and aquaporins, which may in turn participate in leaf opening and closing by affecting sugar distribution, water transport, and ultimately cell turgor pressure in the pulvinus. In this model, the upstream time signal and the downstream transport processes are linked in a single regulatory chain.

The authors are careful to note that some of the transcriptional relationships in the model remain to be functionally validated, and that further work is needed to determine exactly how changes in sugar and water transport translate into the turgor shifts that physically drive leaf movement. Even so, the study provides interconnected evidence spanning phenotype, temporal expression patterns, and molecular regulatory relationships. The direct binding of CCA1 to candidate downstream gene promoters, and the regulation of aquaporin promoter activity by CCA1 and MYB factors, offer concrete research targets for dissecting how plant time signals are transmitted to transport-related processes. Beyond peanut, the findings lay a foundation for exploring how leaf posture regulation connects to water use and environmental adaptation in legumes more broadly, and they bring researchers closer to understanding one of the plant world’s most visible daily rhythms at the level of its underlying genes.

Subject of Research: Circadian and photoperiodic regulation of nyctinastic leaf movement in peanut

Article Title: Peking University Institute of Modern Agriculture reveals molecular regulation mechanism of day opening and night closing in peanut leaves

Article References: Peking University Institute of Modern Agriculture reveals molecular regulation mechanism of day opening and night closing in peanut leaves. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: peanut, nyctinasty, circadian clock, CCA1, MYB transcription factor, SWEET sugar transporters, aquaporins, pulvinus, photoperiod, turgor pressure, legumes, transcriptome

CSA is not an obscure player. It encodes a MYB domain transcription factor that was first identified because a mutation in it starves developing anthers of sugar, leaving plants male sterile. That earlier work, published in 2010, established CSA as a sugar-partitioning gene: it helps route carbohydrates from photosynthetic tissues into the anther, where developing pollen grains are voracious consumers of energy. Later studies delivered a striking twist. The csa mutant is completely male sterile when plants are grown under short-day conditions, but it regains partial fertility under long days. This photoperiod-sensitive male sterility is precisely the property that breeders prize in hybrid rice seed production, because it allows sterile lines to be maintained under one day length and multiplied for hybrid crosses under another. Yet the molecular logic behind that day-length sensitivity has remained murky.

The new study attacks that gap by asking a deceptively simple question: when and where is CSA actually switched on? The researchers measured CSA expression in rice leaves across 24-hour cycles under both short-day and long-day conditions and found that it does not hold steady. Instead, CSA transcript levels oscillate, rising and falling in a regular rhythm under both photoperiods. This oscillatory pattern is the signature of circadian regulation, the roughly 24-hour biological clock that plants, like animals, use to anticipate daily environmental changes. The finding immediately reframed CSA: rather than being a static anther-specific gene, it is a clock-controlled gene whose leaf expression pulses with the day-night cycle.

Crucially, the rhythm is not driven by the clock alone. Light signals, particularly those perceived through the red and far-red photoreceptor phytochromes, also shape the oscillation. This dual control matters because the circadian clock and light signaling pathways are the two great inputs that plants use to measure day length. By showing that both converge on the CSA promoter in leaves, the study provides a mechanistic bridge between photoperiod sensing and male reproductive development. In effect, the leaf reads the calendar and the clock, and the output of that computation is written into the oscillating expression of CSA.

To test whether the leaf rhythm actually matters for fertility, the team used tissue-specific RNA interference to knock down CSA expression specifically in leaves while leaving the anthers untouched. The result was unambiguous: reducing CSA in leaves lowered pollen viability. This experiment overturned the assumption that CSA only needs to function inside the anther itself. The gene must also be expressed, and expressed rhythmically, in leaves for pollen to develop normally. The implication is that the leaf is not merely a sugar factory passively feeding the anther; it is an active regulatory organ whose daily expression program is part of the fertility machinery.

The researchers then dissected the CSA promoter, the stretch of DNA upstream of the gene that hosts the binding sites for regulatory proteins. By generating a series of promoter truncations, they showed that different regions of the promoter carry different responsibilities. Some segments drive expression in anthers, while others are required for the rhythmic pattern in leaves. Both features proved important: the level of CSA expression in anthers and the rhythmic pattern of CSA expression in leaves were each associated with the restoration of male fertility. This promoter-level division of labor explains how a single gene can serve two tissues with distinct regulatory demands, and it suggests that the photoperiod-sensitive sterility of the csa mutant arises from disruption of the leaf-side rhythm rather than from a simple loss of anther expression.

Having localized the regulatory regions, the team went hunting for the proteins that bind them. Using a trio of complementary techniques, dual-luciferase reporter assays in plant protoplasts, yeast one-hybrid screens, and electrophoretic mobility shift assays with purified proteins and labeled DNA probes, they identified two transcription factors that directly target the CSA promoter truncations. The first, PIL11, is a phytochrome-interacting factor-like bHLH protein that binds an E-box motif, a canonical binding site for light-regulated bHLH factors. The second, DOF5, is a member of the plant-specific Dof family of zinc-finger transcription factors and binds a T/AAAAG motif. Both proteins act as direct regulators of CSA transcription, providing the molecular handholds through which light and clock signals grip the gene.

The identity of these regulators is telling. Phytochrome-interacting factors are well known as molecular switches that relay red and far-red light information from phytochromes to the genome, and they also serve as bridges between environmental signals and the circadian clock in other plant systems. Dof factors, meanwhile, have established roles in photoperiodic responses, including the regulation of CONSTANS and flowering time in Arabidopsis, and some rice Dof genes are themselves clock-regulated. By recruiting one factor from each family to the CSA promoter, rice appears to have wired a photoperiod-sensing module, structurally similar to the one that controls flowering, directly into a gene that controls sugar delivery to pollen. The study’s authors describe this as a novel mechanism linking light sensing to circadian-controlled gene expression and thereby connecting photoperiod with male reproductive development.

The agricultural implications are considerable. Hybrid rice, one of China’s great agricultural successes, depends on male-sterile lines to enable large-scale cross-pollination without laborious hand emasculation. Photoperiod-sensitive genic male sterility, the phenomenon in which the csa mutation participates, is especially valuable because sterility can be reversed by changing day length, giving breeders seasonal control over fertility. The new work supplies the first detailed regulatory circuit for that reversal: light quality and the circadian clock converge through PIL11 and DOF5 on the CSA promoter in leaves, generating the rhythmic expression that pollen development requires. Understanding this circuit opens the door to engineering sterility-fertility switches with defined molecular parts, potentially allowing breeders to tune the day-length threshold at which a sterile line becomes fertile, a critical variable for adapting hybrid seed production to different latitudes and climates.

Beyond rice, the study adds to a growing body of evidence that the circadian clock governs reproduction not only by timing the floral transition but by regulating the physiology of the reproductive organs themselves. Previous work has implicated phytochrome-interacting factors in tapetal cell death in tomato anthers and in pollen mitotic division through auxin and sugar metabolism, and rice clock components such as OsLHY have been shown to set critical day lengths for photoperiodic flowering. The new findings extend this theme to the leaf-anther axis, showing that a clock-controlled gene expressed in vegetative tissue is a required component of male fertility. For a crop that feeds roughly half the world’s population, and for a research community racing to redesign photosynthesis and reproductive resilience under climate change, the message is clear: the daily rhythm in the leaf is not background noise. It is part of the score, and pollen fertility dances to it.

Subject of Research: Circadian and light regulation of the CSA gene in rice leaves and its role in photoperiod-sensitive pollen fertility

Article Title: Circadian- and light-regulated oscillatory expression of CSA in rice leaves is required for pollen fertility

Article References: Circadian- and light-regulated oscillatory expression of CSA in rice leaves is required for pollen fertility. (n.d.). https://doi.org/10.1007/s00299-026-03976-6

Image Credits: AI Generated

DOI: 10.1007/s00299-026-03976-6

Keywords: rice, circadian clock, CSA, photoperiod-sensitive male sterility, pollen fertility, PIL11, DOF5, phytochrome, anther development, sugar partitioning, hybrid rice, transcription factors

Ionizing radiation kills cells primarily by generating DNA double-strand breaks, the most lethal form of genetic damage. Cells respond with two principal repair strategies: homologous recombination, which operates in the S and G2 phases of the cell cycle and uses an intact sister chromatid as a template, and non-homologous end joining, which is available throughout the cell cycle and directly ligates broken DNA ends. The Ku heterodimer, composed of the Ku70 and Ku80 proteins, sits at the very front line of non-homologous end joining. It recognizes broken DNA ends within seconds of their formation, encircles the free DNA terminus like a sliding clamp, and recruits the downstream enzymatic machinery needed to process and rejoin the break. Without Ku, double-strand breaks accumulate, chromosomal aberrations multiply, and cells become exquisitely sensitive to radiation.

The new research reveals that the assembly of the Ku70-Ku80 heterodimer itself is not a spontaneous, unregulated event but a process actively promoted by a complex containing TIMELESS and SIRT1. TIMELESS, best known for its role in maintaining circadian clocks and stabilizing replication forks, had previously been implicated in the DNA damage response, but its precise contribution to double-strand break repair remained murky. The study now positions TIMELESS as a scaffold that brings together SIRT1 and Ku70, creating a microenvironment in which Ku70 is kept in a state favorable for pairing with its partner Ku80. SIRT1, an NAD-dependent deacetylase, modifies Ku70 by removing acetyl groups, a chemical change that appears to facilitate the proper folding and interaction of Ku70 with Ku80 and with damaged DNA.

Using a combination of co-immunoprecipitation, proximity ligation assays, and live-cell imaging of DNA repair factor recruitment, the investigators demonstrated that cells lacking TIMELESS or SIRT1 show a marked deficit in Ku heterodimer formation. When the researchers depleted TIMELESS, Ku70 failed to associate efficiently with Ku80, and the recruitment of Ku to laser-induced DNA damage tracks was visibly delayed. The same phenotype emerged when SIRT1 was inhibited pharmacologically or knocked down genetically, indicating that the deacetylase activity of SIRT1 is a functional requirement, not merely a passive component of the complex. Rescue experiments in which wild-type SIRT1 was reintroduced restored Ku assembly, whereas catalytically inactive SIRT1 mutants did not, pinpointing the enzymatic activity as the decisive factor.

The consequences for radiation sensitivity were striking. Cancer cells deficient in TIMELESS or SIRT1 accumulated more residual double-strand breaks after irradiation, displayed elevated levels of chromosome breaks and micronuclei, and died at substantially higher rates following clinically relevant doses of radiation. Conversely, cells engineered to overexpress the TIMELESS-SIRT1-Ku70 module became more resistant, repairing radiation-induced breaks faster and surviving doses that killed their normal counterparts. The effect was specific to the Ku pathway: markers of homologous recombination were largely unaffected, suggesting that the complex operates selectively on non-homologous end joining rather than globally boosting all forms of DNA repair.

What makes this discovery particularly compelling is the cast of characters involved. SIRT1 has long fascinated biologists because of its links to calorie restriction, aging, and metabolism, and pharmacological SIRT1 activators have been pursued as potential anti-aging therapeutics. TIMELESS connects the study to the circadian clock, raising the tantalizing possibility that the daily rhythm of a cell’s repair capacity may be governed, at least in part, by the oscillating availability of this complex. Clinicians have long observed that the timing of radiotherapy within the day can influence outcomes in some cancers, and a molecular bridge between clock proteins and DNA repair machinery offers a plausible mechanistic underpinning for such observations. If TIMELESS abundance or activity fluctuates with the cell’s internal clock, the efficiency of Ku assembly, and therefore of end joining, might fluctuate with it.

For oncology, the immediate implication is that the TIMELESS-SIRT1-Ku70 axis represents a candidate target for radiosensitization. Drugs that disrupt the complex, inhibit SIRT1’s deacetylase activity in tumors, or prevent the recruitment of Ku to broken DNA could strip cancer cells of a key survival advantage and make radiation therapy more effective at lower doses. This matters because dose escalation is often limited by damage to surrounding healthy tissue; a radiosensitizer that preferentially compromises tumor cell repair would widen the therapeutic window. The study’s demonstration that SIRT1 inhibition phenocopies TIMELESS loss is especially encouraging from a translational standpoint, since SIRT1 inhibitors already exist as research tools and are being explored in other disease contexts.

The findings also carry a cautionary note for interpreting tumor biology. High levels of TIMELESS have been reported in several malignancies and have been associated with poor prognosis, an observation often attributed to the protein’s role in supporting replication stress tolerance and cell proliferation. The new work adds a second, complementary explanation: tumors that overexpress TIMELESS may also be intrinsically more resistant to radiotherapy because their Ku assembly machinery runs at full throttle. This could help explain why some patients with seemingly similar tumors respond dramatically differently to the same radiation regimen, and it suggests that TIMELESS expression levels might serve as a biomarker for predicting radiosensitivity and guiding treatment decisions.

As with any mechanistic study, important questions remain. The precise structural details of how TIMELESS docks onto Ku70 and how SIRT1’s deacetylation of Ku70 alters the heterodimer’s DNA-binding properties will require biochemical and structural characterization. It is also not yet clear whether the complex acts at the break site itself or in the nucleoplasm before Ku ever encounters damaged DNA, and whether additional factors participate in the assembly process. Translating the findings into the clinic will demand evidence that the axis operates in human tumors in vivo and that its disruption does not catastrophically sensitize normal tissues, which also rely on Ku-mediated repair to survive radiation. Nonetheless, by illuminating a previously hidden regulatory step in one of the cell’s most fundamental repair pathways, the study opens a concrete new avenue for making radiation therapy work harder against cancer, and it reinforces a growing theme in modern oncology: the most effective treatments may come not from hitting tumors harder, but from quietly dismantling the molecular machinery that lets them endure.

Subject of Research: A TIMELESS-SIRT1-Ku70 protein complex that promotes Ku heterodimer assembly and confers radioresistance to cancer cells through enhanced non-homologous end joining DNA repair.

Article Title: A TIMELESS-SIRT1-Ku70 complex confers radioresistance to cancer cells by promoting Ku heterodimer assembly

Article References: A TIMELESS-SIRT1-Ku70 complex confers radioresistance to cancer cells by promoting Ku heterodimer assembly. (n.d.). https://doi.org/10.1038/s41420-026-03363-w

Image Credits: AI Generated

DOI: 10.1038/s41420-026-03363-w

Keywords: TIMELESS, SIRT1, Ku70, Ku80, DNA double-strand breaks, non-homologous end joining, radioresistance, radiation therapy, DNA repair, circadian clock, cancer, radiosensitization

Circadian clocks are built from interlocking transcriptional feedback loops. In Drosophila, the core loop involves the transcriptional activators CLOCK and CYCLE driving expression of the period (per) and timeless (tim) genes, whose protein products accumulate, enter the nucleus, and repress their own transcription. This oscillation takes roughly twenty-four hours to complete, and its phase and amplitude are tuned by light input pathways, post-translational modifications, and a web of downstream output genes that translate molecular time into behavior and physiology. Because virtually every aspect of fly biology—locomotor activity, feeding, mating, olfaction, and even susceptibility to pesticides—rhythms with the day, variation in clock function has profound fitness consequences.

Yet despite decades of work identifying core clock genes in laboratory strains, relatively little has been known about how natural genetic variation modifies the clock in wild populations. Classical forward genetics, which relies on mutagenesis and large-effect alleles, tends to uncover genes whose disruption produces dramatic phenotypes. Most naturally occurring variation, by contrast, is subtle and regulatory: it changes how much, when, or where a gene is expressed rather than altering the protein sequence itself. Detecting this kind of variation requires a different approach—one that surveys the entire transcriptome for associations between genetic markers and gene expression levels. That is precisely what an eQTL analysis delivers.

The logic of eQTL mapping is conceptually straightforward. Researchers genotype a panel of genetically distinct individuals at hundreds of thousands of single nucleotide polymorphisms and simultaneously measure gene expression, typically by RNA sequencing, in a relevant tissue or under a relevant condition. Statistical association testing then identifies genomic regions—the eQTLs—where genotype predicts expression of one or more genes. When a variant influences expression of a nearby gene, it is called a cis-eQTL, and it often points to a regulatory element such as an enhancer or promoter directly linked to that gene. When a variant influences expression of distant genes, often many at once, it is called a trans-eQTL, and it frequently implicates a diffusible regulator such as a transcription factor whose own activity varies genetically across the population.

Applied to the circadian system, this approach can reveal the full regulatory architecture of the clock: not just the core loop genes that biologists have studied for forty years, but the constellation of modifiers, chromatin regulators, signaling molecules, and output factors whose expression is under genetic control. In Drosophila, the availability of inbred lines derived from a single natural population, combined with dense genomic resources and well-characterized rhythmic transcriptomes, makes the species an ideal platform for this kind of analysis. The fly’s clock is also remarkably conserved at the level of mechanism, sharing its fundamental design with clocks in mammals, including humans, which means lessons learned in Drosophila frequently illuminate human chronobiology.

The significance of mapping circadian eQTLs extends beyond basic biology into ecology and evolution. Populations of Drosophila melanogaster span enormous environmental gradients, from the tropics to temperate Europe, and they encounter dramatic seasonal variation in day length, temperature, and resource availability. Clock properties such as the period of the free-running rhythm, the phase of activity relative to dawn and dusk, and the robustness of rhythmicity under temperature fluctuations all show heritable variation in natural populations. This variation matters because a fly whose internal day is mismatched to the external day may forage at the wrong time, miss mating opportunities, or fail to enter the correct diapause before winter. Local adaptation of clock parameters is therefore expected, and the genetic substrate of that adaptation should be visible as allele-frequency differences at eQTLs controlling clock-related genes.

Genome-wide association studies of behavioral rhythms have previously identified candidate loci, but connecting behavioral phenotypes to specific molecular mechanisms has remained difficult. eQTL analysis offers a bridge. If a genetic variant associated with altered locomotor rhythms also acts as an eQTL for a known clock gene, the chain of causation from DNA sequence to regulatory change to molecular oscillation to behavior becomes traceable. Conversely, trans-eQTL hotspots—genomic loci that regulate large modules of co-expressed rhythmic genes—can point to previously unrecognized master regulators of the clock, generating hypotheses that can be tested with targeted mutagenesis and reporter assays. In this way, population-level statistical mapping and mechanistic molecular biology reinforce one another.

The study also speaks to a broader theme in modern genetics: the primacy of regulatory variation in adaptation. Since the completion of the Drosophila melanogaster reference genome and the subsequent sequencing of hundreds of wild-derived strains, it has become increasingly clear that changes in gene regulation, rather than protein-coding changes, supply much of the raw material for evolution. Enhancers can evolve rapidly because they are modular—a change in one regulatory element need not disrupt the protein’s function elsewhere. For a system like the circadian clock, whose components are used in multiple tissues and developmental stages, this modularity is essential. An eQTL map makes this architecture explicit, showing which regulatory connections are constrained and which are free to vary, and thereby revealing the evolutionary pathways available to the clock.

There are, of course, important caveats and open questions. eQTL studies measure expression at a snapshot in time, whereas the clock is inherently dynamic; expression levels of clock genes oscillate with a period of about a day, and the effect of a variant may depend on the time of day at which tissue is collected. Time-of-day-specific eQTL mapping, in which expression is assayed at multiple circadian time points, can capture this temporal dimension and has revealed in other systems that a large fraction of eQTLs act only at certain phases. Environmental context matters as well: temperature cycles and light conditions can mask or unmask genetic effects on expression. Integrating eQTL data with chromatin accessibility maps, transcription factor binding data, and longitudinal behavioral recordings will be needed to convert statistical associations into a complete mechanistic model of clock adaptation.

Even with these caveats, the genome-wide eQTL framework established in Drosophila melanogaster marks a substantial advance in understanding how circadian systems are wired and how they evolve. It provides a catalog of regulatory variants that can be interrogated experimentally, a set of candidate loci for adaptation to seasonal and climatic gradients, and a template for similar analyses in other species, including crop plants and livestock, where circadian timing influences yield, fertility, and disease resistance. As sequencing costs continue to fall and temporal transcriptomic datasets accumulate, the vision of a complete, genotype-to-phenotype map of the biological clock—one that explains not only how the clock works but how it adapts—is moving steadily closer to reality. For a rhythm that has been ticking in nearly every organism on Earth for billions of years, the genetic grammar of its flexibility is finally coming into focus.

Subject of Research: Genome-wide eQTL analysis of circadian clock adaptation in Drosophila melanogaster

Article Title: Mapping the regulatory architecture of circadian clock adaptation: A genome-wide eQTL analysis in Drosophila melanogaster

Article References: Yair, M., Fishman, B., Aslan, M., & Tauber, E. (2026). Mapping the regulatory architecture of circadian clock adaptation: A genome-wide eQTL analysis in Drosophila melanogaster. Heredity. https://doi.org/10.1038/s41437-026-00886-x

Image Credits: AI Generated

DOI: 10.1038/s41437-026-00886-x

Keywords: circadian clock, eQTL, Drosophila melanogaster, gene expression, regulatory variation, adaptation, quantitative genetics, chronobiology, natural populations, transcriptional feedback loop, Mapping, regulatory