Researchers first identified piRNAs as repressors of transposable elements, and later studies identified additional functions. The reviewed evidence links PIWI–piRNA activity to epigenetic programming, maintenance of maternal transcript homeostasis and control of processes involved in early embryonic development. These findings broaden the pathway’s apparent regulatory reach beyond its initial association with transposable-element repression.

The review examines the biogenesis and biological functions of PIWI/piRNA complexes and compares their biology across species. Its central finding is that this regulatory framework is neither uniform nor interchangeable between organisms. Conserved functions coexist with sex-specific and species-specific patterns, making the broader biology of the pathway dependent on the biological context in which it operates.

Three forms of variation stand out in the comparative literature: sex- and species-specific patterns of piRNA expression, differences in the organization of piRNA clusters, and functional diversity among PIWI proteins. The authors suggest that these differences may reflect the range of reproductive strategies and evolutionary adaptations represented among the species examined. The review does not reduce that variation to a single model of PIWI–piRNA control.

Disruption of the piRNA pathway has also been associated with infertility and germ-cell tumors in studies involving various species. The evidence is not uniform, however, because the organisms differ and the reported relationships vary in character. Some associations are described as mechanistic, while others are correlative, leaving their basis and broader relevance uncertain.

This qualification matters for interpreting disease-related findings. An association between pathway disruption and infertility in one species does not by itself establish an equivalent causal mechanism in another, and the reported links with germ-cell tumors likewise cannot be assumed to share one biological basis. The review instead treats these observations as evidence that requires more detailed cellular and clinical assessment.

The authors identify cellular regulation of piRNAs and the clinical relevance of PIWI–piRNA biology as important underexplored areas. They also call for further study of the pathway to clarify where functions are conserved, where they are species-specific and how piRNA organization relates to the reproductive biology of different organisms.

Overall, the review characterizes PIWI–piRNA complexes as a versatile regulatory system involved in genome maintenance, germ-cell function, maternal transcript regulation and early development. It also emphasizes that piRNA expression patterns, cluster organization and PIWI protein functions cannot be assumed to be identical across sexes or species. The work is a synthesis of the existing literature rather than a new experiment or clinical assessment, and its most important conclusion is both structural and cautionary: PIWI–piRNA biology is broadly relevant, but its detailed mechanisms remain context dependent.

Subject of Research: Comparative functions and regulation of PIWI–piRNA complexes in germ cells and early embryonic development

Article Title: The Role of RNA Interactions with PIWI in Regulating Gametogenesis, Fertilization, and Early Development Across Species

Article References: Haddadi, M., Safari-Alighiarloo, N., Mikaeeli, G., Meftagh, M. S., & Jazayeri, M. (2026). The Role of RNA Interactions with PIWI in Regulating Gametogenesis, Fertilization, and Early Development Across Species. Reproductive Sciences. https://doi.org/10.1007/s43032-026-02248-8

Image Credits: AI Generated

DOI: 10.1007/s43032-026-02248-8

Keywords: PIWI proteins, piRNAs, small RNAs, germ cells, early development, epigenetic regulation, maternal transcripts, transposable elements, comparative biology, infertility, germ-cell tumors, Role

The story begins with physics. Shortly after Thomas Young described visual optics and accommodation in the human eye in 1801, researchers turned to fish. In water, the cornea loses nearly all of its refractive power, so the lens must do the focusing alone. That simplification made the dense, spherical fish lens an ideal natural model. Ludwig Matthiessen exploited this in a landmark series of studies, showing that fish lenses lack spherical aberration and defining what became known as Matthiessen’s ratio: the focal length of the lens is roughly 2.55 times its radius. He even demonstrated that whales and dolphins, mammals that returned to the sea, convergently evolved the characteristic optics of fishes. Theodor Beer added a crucial twist: because fish lenses are so dense they cannot change shape, so they accommodate by moving within the eye instead.

Modern imaging has only deepened the appreciation of aquatic lens optics. Fish eyes typically have short focal lengths and large pupils to maximize light capture, which creates strong chromatic aberration—a serious problem for shallow-water species with vivid color vision. Their solution is a multifocal lens that focuses different wavelengths onto different planes, something the monofocal human lens does not do. Remarkably, the optics remain adjustable throughout life. In the cichlid fish Haplochromis burtoni, individuals raised under monochromatic light developed lenses with altered gradient refractive index properties, and in a related cichlid, the lens shifted toward monofocal optics in the dark-adapted state, presumably matching rod-dominated vision. How organelle-free fiber cells accomplish this optical tuning remains an open question.

Aquatic models have also become central to understanding myopia, the most common visual disorder in humans. When researchers covered the eyes of Nile tilapia with diffusers that induce form-deprivation myopia, the fish responded like birds and mammals, integrating visual input into the regulation of eye growth—without any change in lens optics. Zebrafish have since emerged as a genetic platform for emmetropization studies, with optical coherence tomography used to quantify eye dimensions and multiple myopia-related genes identified. The four-eyed fish Anableps, which sees simultaneously in air and water through a pear-shaped lens with distinct aerial and aquatic optical zones, and the sunburst diving beetle larva, whose tubular bifocal eyes scan the environment, illustrate the extraordinary range of solutions evolution has produced for the same focusing problem.

The lens’s transparency and high refractive power depend on crystallin proteins, and aquatic species provided the first evidence that these proteins were co-opted from metabolic enzymes and stress-response proteins—a foundational model for gene sharing. Fishes express all three ubiquitous vertebrate crystallin families, plus abundant methionine-rich γM-crystallins not found in terrestrial vertebrates. Comparative biochemistry revealed that α- and β-crystallins co-elute in fish lenses, suggesting interactions absent in mammals. Squid lenses, built from a single crystallin type descended from a glutathione S-transferase ancestor with 25 differentially expressed variants under positive selection, show that the same evolutionary strategy—recycling stress and detoxification genes—arose independently in invertebrates.

Temperature extremes have turned fish lenses into natural laboratories for protein stability. McFall-Ngai and Horwitz compared lenses from 12 species spanning physiological temperatures from -2°C in Antarctic icefish to 47°C in desert lizards, finding that species adapted to heat resisted temperature-induced opacity better, with α-crystallins most resistant to aggregation. The Antarctic toothfish, which lives at -2°C, has become a star model: its αA-crystallin carries a valine-to-threonine substitution that alters surface hydrophobicity and oligomer stability, and its γS-crystallin remains structurally stable up to 56-63°C—far above its physiological temperature. Its lens also stays clear after 48 hours at -12°C, while a tropical fish develops nuclear opacity at 0°C. Biophysical analysis of six toothfish γ-crystallins showed that the liquid-liquid phase separation underlying cold cataract depends on charged-residue interactions rather than thermal stability, offering a model for manipulating protein stability by design.

Zebrafish, with their duplicated teleost genomes, have dissected multifunctional proteins into separable roles. The single mammalian aquaporin 0 water channel exists as two zebrafish paralogs: Aqp0a serves as the primary water channel, while Aqp0b shows stronger auto-adhesion due to a single amino acid substitution. CRISPR mutants revealed that loss of Aqp0a prevents the developmental centralization of the lens nucleus, destabilizes the anterior suture, and produces age-related opacity—even though the maximum refractive index is still reached. Similarly, zebrafish carry two αB-crystallin paralogs with divergent expression: the lens-preferred αBa-crystallin doubles cataract incidence at 24 months when lost, suggesting it stabilizes other lens proteins during aging, while αA-crystallin acts as a stronger chaperone at zebrafish physiological temperatures. Far from being a complication, gene duplication provides a powerful tool for separating protein functions.

Aquatic species have illuminated lens development with unmatched precision. Zebrafish form their lens by delamination rather than invagination, never producing a hollow vesicle, yet cell fate mapping by Greiling and Clark showed that central placode cells become primary fiber cells while lateral cells become epithelium—a pattern conserved with the mouse. The most striking recent discovery came from CRISPR screening: the phospholipase gene plaat1 is required for fiber cell organelle removal in zebrafish, and knockout of the mouse ortholog Plaat3 produces the same organelle retention, revealing a conserved mechanism regulated by Hsf4 that targets organelle membranes for degradation. Because keratinocytes and erythrocytes also lose organelles during differentiation, understanding this process has significance far beyond the eye.

Regeneration is where aquatic species truly shine. Newts can regenerate a fully functional lens from dorsal iris pigment epithelial cells repeatedly, without diminishing capacity, and recent work shows macrophages facilitate the process. The African clawed frog regenerates its lens from corneal epithelial cells, even in post-metamorphic animals, and apoptosis is required for regeneration but not initial development. Perhaps most dramatic is the Mexican tetra, whose cave-dwelling populations evolved degenerate eyes over roughly 10,000 years: transplanting a surface-fish lens into a cave-fish embryo restored normal eye development, proving that lens signals sustain retinal growth. These systems are informing early efforts toward human lens regeneration.

Looking forward, the review points to zebrafish as a cost-effective aging model—roughly 27 percent of wildtype fish develop lens opacity by 18 months—and to expanding -omics approaches, including a single-cell transcriptomic atlas of the vertebrate lens and proteomics that quantifies over 13,000 proteins in the tiny zebrafish lens. Farmed fish, from salmon with diet-linked cataracts to lumpfish with prevalence approaching 100 percent, offer practical models for cataract prevention. Two hundred years after Matthiessen first measured a fish lens, aquatic species remain not just historical footnotes but active engines of discovery in lens biology, with direct implications for treating human blindness, myopia, and age-related cataract.

Subject of Research: Contributions of aquatic organisms to understanding the vertebrate ocular lens

Article Title: Contributions of aquatic organisms to understanding the vertebrate ocular lens

Article References: Posner, M. (2026). Contributions of aquatic organisms to understanding the vertebrate ocular lens. Frontiers in Ophthalmology, 6, Article 1900415. https://doi.org/10.3389/fopht.2026.1900415

Image Credits: AI Generated

DOI: 10.3389/fopht.2026.1900415

Keywords: ocular lens, aquatic models, zebrafish, crystallins, lens regeneration, myopia, cataract, Antarctic toothfish, lens development, comparative biology, Contributions, aquatic

The article, written by K. C. Kent Lloyd of the Department of Surgery and Mouse Biology Program at the University of California, Davis, lays out a problem that has grown quietly urgent as biomedical research shifts away from animal-heavy experimentation. The vocabulary and standards for validating NAMs were largely developed for toxicology and chemical safety testing, where the questions are narrow and well-defined: does this chemical cause skin sensitization, genotoxicity or organ injury? In those settings, reference chemicals, positive and negative controls and performance metrics can be specified in advance. Federal coordination through the Interagency Coordinating Committee on the Validation of Alternative Methods, known as ICCVAM, and the NICEATM program, which moved into the NIH Office of Research Innovation, Validation, and Application in June 2026, has advanced this work considerably. But biomedical discovery research is a different animal entirely.

When a researcher studies Alzheimer’s disease, cancer, fibrosis, immune dysfunction or metabolic disease, they often do not know in advance which cell type, tissue, developmental stage or systemic interaction will prove most important. A human organoid might faithfully reproduce one aspect of a disease while completely missing immune, endocrine, vascular, neural, metabolic or biomechanical influences. A computational model may predict an outcome beautifully in one dataset yet fail in another. A microphysiological system may capture a tissue interface without reproducing whole-body pharmacology. These are not failures of the technology; they are gaps between what a model can do and what a scientist needs it to do, and Lloyd argues that independent testing infrastructure is the missing piece that can identify those gaps before they derail a research program.

The UC Davis NAMs Testing Center approaches this challenge by drawing on expertise that rarely resides in a single laboratory. As a campus-wide resource, it assembles capabilities from biomedical engineering, comparative biology, pathology, genetics, imaging, phenotyping, veterinary medicine and human health research. The university’s academic health system, its Schools of Medicine and Veterinary Medicine, the Mouse Biology Program, the National Biomedical Research Institute, the Comprehensive Cancer Center and specialized research cores all contribute. A steering committee of campus administrators and faculty advisors guides priorities and coordinates participation across units. The result is a facility that can pull together whatever combination of expertise a particular scientific question demands, rather than forcing every project through the same pipeline.

Several capabilities are already operational through participating UC Davis programs. These include patient-derived xenograft models, full necropsy and histopathology services, x-ray, microPET and microCT imaging, and in vivo phenotyping pipelines that span cardiovascular, respiratory, neurological and behavioral, ophthalmic, auditory, metabolic and endocrine, digestive, hematological, immune, musculoskeletal, renal, reproductive and embryonic systems. Projects can also draw on transcriptomic, proteomic and metabolomic analyses and, with appropriate approvals, clinical specimens from UC Davis biorepository resources. A single fit-for-purpose study might combine human cells or organoids with quantitative imaging, molecular profiling, computational analysis and an orthogonal comparator that measures the relevant biology in a completely different way.

The Center’s evaluation framework distinguishes between three levels of evidence. Verification addresses technical reliability: control performance, repeatability, quality-control criteria, reagent or operator effects and whether the method can be transferred to another laboratory under defined conditions. Validation refers more broadly to evidence that a method can support a defined inference in its stated context of use. Qualification is reserved for formal acceptance by a regulatory or other decision-making authority when such a pathway applies. Fit-for-purpose assessment ties the amount and type of evidence to the intended use rather than to a universal validation label. These distinctions align with recent confidence frameworks that emphasize context of use, biological relevance, technical characterization, transparency and independent review.

Biological evaluation asks whether the model actually contains the features needed for the domain of inference. A fibrosis model, for example, may require matrix-producing cells, inflammatory signaling and enough time for tissue remodeling to occur. A tumor model intended to predict immune-mediated response must include relevant immune biology, not just cancer-cell growth. Comparative testing is then selected according to the question: a NAM may need comparison with human tissues, clinical data, another NAM, an existing dataset or a carefully designed in vivo study. No single comparator serves as a gold standard for every application. Discordant results, where a NAM, an animal model and human data disagree, can be among the most informative outcomes, pointing to missing biology, species differences, inappropriate exposure conditions or limitations in the comparator itself.

The Center is currently supporting studies that integrate patient-derived, 3D-bioprinted tumor models with orthogonal in vivo tumor models to evaluate therapeutic response and mechanism. In an ongoing bladder cancer study, responses observed in the 3D platform are compared with an established syngeneic bladder cancer model developed through the Center, while machine-learning analysis of tumor morphology and large human cancer datasets is used to assess mechanism and potential patient relevance. This workflow demonstrates how complementary NAM, animal and human data can be integrated to evaluate both biological validity and translational relevance in a single coordinated effort.

The Center occupies a deliberately different position from organizations that set regulatory requirements. ICCVAM and D-NICEATM/ORIVA coordinate federal validation support, the FDA’s ISTAND program provides a qualification pathway for novel drug development tools, and OECD guidance and EURL ECVAM offer international frameworks. The NIH Complement-ARIE Validation and Qualification Network is building standardized evidence packages for NAMs but does not itself confer regulatory qualification. The UC Davis Center functions as a hands-on testing node, helping to define studies, carry out independent comparative or transferability testing, and assemble evidence that investigators, funders, industry or regulatory programs can use. It does not confer regulatory acceptance, and it manages conflicts of interest through institutional review, recusal or independent oversight, with blinded evaluation of coded samples when knowledge of experimental conditions could influence assessment.

Trust, Lloyd argues, will ultimately determine how quickly useful NAMs are adopted in biomedical research. Independent testing centers can contribute by providing comparative expertise, reproducibility testing and evidence that is separate from the developer’s own evaluation. The goal at UC Davis is a domain-of-inference statement that describes what a model can support, what remains uncertain and which evidence was used to reach that conclusion, which is far more informative to subsequent users than a general label of validated. A negative or discordant result can be genuinely valuable if it identifies a limitation before a model is used more widely. Similar testing nodes, connected through national and international networks, could provide a practical route from method development to evidence-based use, ensuring that the next generation of human-based models earns its place in the research arsenal on merit rather than on promise.

Subject of Research: Independent testing infrastructure for validating New Approach Methodologies in biomedical research

Article Title: Independent testing infrastructure for new approach methodologies: the UC Davis NAMs testing center

Article References: Lloyd, K. C. K. (2026). Independent testing infrastructure for new approach methodologies: the UC Davis NAMs testing center. Frontiers in Medical Technology, 8, Article 1966220. https://doi.org/10.3389/fmedt.2026.1966220

Image Credits: AI Generated

DOI: 10.3389/fmedt.2026.1966220

Keywords: NAMs, organoids, microphysiological systems, validation, UC Davis, biomedical research, drug development, comparative biology, reproducibility, ICCVAM, NIH, animal models

The central problem the forum addressed is one that has long frustrated the longevity field: aging is a complex, multifactorial process, and without reliable molecular measures of biological age it is extraordinarily difficult to demonstrate that any candidate intervention actually slows it. Chronological age is a poor proxy, because individuals of the same age can differ dramatically in health status, disease risk and physiological reserve. Biomarkers of aging, measurable indicators that track biological aging more faithfully than the passage of time, therefore serve as the linchpin for translating laboratory discoveries into clinical trials. The forum’s organizers argued that the field has reached a point where such frameworks must be standardized, validated and deployed in human studies rather than remaining confined to retrospective cohort analyses.

Among the most prominent themes was the continued evolution of epigenetic clocks, the DNA methylation-based estimators of biological age pioneered by Steve Horvath of the University of California, Los Angeles, who presented at the meeting. Horvath and collaborators recently described pan-mammalian clock models in Nature Communications in 2024, extending methylation-based age estimation across species and tissues. These models exploit the fact that cytosine methylation patterns at specific genomic sites change predictably with age, allowing regression-based models trained on large reference datasets to predict chronological age from a tissue sample. Deviations between predicted and chronological age, the so-called age acceleration, have been associated in numerous studies with mortality risk and age-related disease. The forum discussions reportedly focused on refining these tools, including second-generation clocks trained on mortality and morbidity outcomes rather than chronological age alone, and on the interpretive caveats that arise when clocks are used to evaluate interventions.

That caveat is a serious one, and it featured prominently in the technical discussions. Work published in Cell Metabolism in 2023 by Poganik and colleagues demonstrated that biological age, as read out by multiple independent biomarkers, is not a fixed quantity but can fluctuate in response to stress, surgery and severe illness, and can recover afterward. This transient age acceleration and subsequent restoration implies that a single snapshot of a biomarker may mislead trial designers, and that repeated longitudinal sampling is essential to distinguish durable rejuvenation from short-term perturbation. Forum participants emphasized that intervention trials must therefore incorporate repeated measurements, appropriate control groups and pre-registered analytical pipelines to avoid spurious conclusions about whether a treatment has genuinely slowed aging.

A second major strand concerned organ-specific and proteomic aging clocks. Rather than estimating the age of the whole organism, these models estimate the biological age of individual organs or physiological systems, revealing that organs within a single person can age at markedly different rates. Recent work published in Cell Metabolism in 2025 by Goeminne and colleagues, and other proteomic studies discussed at the forum, showed that plasma protein signatures can be decomposed into organ-derived aging signals, opening the possibility of identifying which organ is failing fastest in a given individual and tailoring interventions accordingly. Related work by Yu and colleagues in Cell Metabolism in 2024 and by Bi and colleagues in 2025 extended this organ-centric view, and presentations by researchers including Jing-Dong J. Han of Peking University and Guangju Ji of the Henan Academy of Sciences covered multi-omic and computational approaches to constructing and validating such signatures in large human cohorts.

Inflammation emerged as a recurring mechanistic thread connecting many of the biomarkers under discussion. David Furman of Stanford University and the Buck Institute for Research on Aging presented work on immune-system aging, including the inflammatory signature known as iAge, described in Nature Aging in 2021, which uses a small set of circulating immune and chemokine markers to predict age-related decline and multimorbidity. Because chronic low-grade inflammation, sometimes termed inflammaging, contributes to a broad range of age-associated pathologies, immune-focused biomarkers offer a mechanistically interpretable complement to epigenetic and proteomic clocks. Furman’s discussion of iAge also illustrated the translational pathway the forum sought to highlight, since the signature has been developed into a commercial platform intended to support clinical decision-making and intervention monitoring.

Cellular senescence, the state of irreversible growth arrest that accumulates in aged tissues and secretes inflammatory and matrix-degrading factors, formed another pillar of the program. Presentations by Ning Jiang of West China Hospital and other speakers addressed the identification and quantification of senescent cell burden in accessible tissues and biofluids, a prerequisite for testing senolytic drugs, the compounds designed to selectively eliminate senescent cells. The field’s challenge, as framed at the forum, is that senescence markers such as p16INK4a, senescence-associated beta-galactosidase and the senescence-associated secretory phenotype are heterogeneous and context-dependent, so a validated circulating biomarker panel for senescent cell load remains an urgent unmet need for the senolytics pipeline.

The forum also looked beyond humans to comparative biology as a source of intervention targets. Vera Gorbunova and Andrei Seluanov of the University of Rochester presented their work on long-lived and cancer-resistant rodents, including naked mole-rats and blind mole-rats, whose unusual genome maintenance and tumor-suppression mechanisms were detailed in a 2025 Nature paper by Firsanov and colleagues. Comparative studies of this kind identify naturally evolved protective mechanisms, such as enhanced DNA repair, high-molecular-mass hyaluronan and distinctive interferon responses, that can in principle be mimicked pharmacologically. Complementing this, Vincenzo Sorrentino of the National University of Singapore and Lu Dong discussed mitochondrial and proteostatic determinants of tissue aging, including work on NAD metabolism and the nutraceutical trigonelline published in Nature Metabolism in 2024, which linked circulating trigonelline levels to muscle mitochondrial function and suggested a plausible route to combating sarcopenia.

Genome instability and the limits of rejuvenation were addressed by Jan Vijg of Albert Einstein College of Medicine, whose presentations considered somatic mutation accumulation as a fundamental driver of aging and the implications this holds for how much biological age reversal is realistically achievable. Ana Maria Cuervo of Albert Einstein College of Medicine discussed chaperone-mediated autophagy, the selective lysosomal degradation pathway that declines with age, and the therapeutic prospects of pharmacologically restoring it. Raul Mostoslavsky of Massachusetts General Hospital and Harvard Medical School covered chromatin and metabolic regulation of aging, while Susanna Rosi of Altos Labs presented work on cellular reprogramming and neural rejuvenation, an approach that resets epigenetic age in specific cell populations and has shown functional recovery in models of brain injury and neurodegeneration.

The report closes by looking forward: the organizers announced a 7th TimePie Longevity Forum for 2026, and the emerging directions summarized in the meeting report point toward standardized, multi-modal biomarker panels that combine epigenetic, proteomic, immune and imaging readouts, deployed in longitudinal human cohorts and intervention trials. The competing-interest disclosures accompanying the report, which include inventorship on epigenetic biomarker patents, company founder roles and advisory positions among several authors, underscore how quickly the field is moving from academic measurement toward commercial application. What the Shanghai meeting made clear is that the bottleneck in geroscience is no longer the identification of candidate targets in model organisms but the credible demonstration, in people, that a therapy has changed the trajectory of biological aging, and that this demonstration will stand or fall on the quality of the biomarkers used to measure it.

Subject of Research: Aging biomarker development and geroscience intervention discovery discussed at the 6th TimePie Longevity Forum in Shanghai

Article Title: Advancing aging biomarkers and intervention discovery at the TimePie Longevity Forum

Article References: Ying, K., Bie, J., Chen, G., Cuervo, A. M., Deng, H., Dong, L., Furman, D., Gorbunova, V., Han, J.-D. J., Horvath, S., Ji, G., Jiang, N., Mostoslavsky, R., Rosi, S., Seluanov, A., Sorrentino, V., Tang, Y., Vijg, J., & Yang, Q. (2026). Advancing aging biomarkers and intervention discovery at the TimePie Longevity Forum. Nature Aging. https://doi.org/10.1038/s43587-026-01226-8

Image Credits: AI Generated

DOI: 10.1038/s43587-026-01226-8

Keywords: aging biomarkers, epigenetic clocks, geroscience, longevity forum, cellular senescence, proteomic aging clocks, inflammaging, senolytics, chaperone-mediated autophagy, somatic mutations, comparative biology, NAD metabolism

The central paradox the authors confront is chemical. ROS—including superoxide, hydrogen peroxide and hydroxyl radicals—are inherently reactive, which is precisely why uncontrolled ROS production is toxic. Yet evolution has exploited this very reactivity. Hydrogen peroxide, in particular, is small, electrically neutral and membrane-permeable, allowing it to diffuse rapidly through tissue and act as a broadcast signal. At wound margins, ROS can oxidize the cysteine residues of target proteins, reversibly altering the activity of phosphatases, kinases and transcription factors. In this way, a transient oxidative pulse functions as a second-messenger system, converting the physical fact of injury into a coordinated genetic and cellular response. The review frames this as oxidative eustress—beneficial, regulated stress—as opposed to the destructive oxidative distress associated with pathology.

What makes the new synthesis compelling is its comparative breadth. The authors assemble evidence spanning the metazoan tree, from cnidarians such as Hydra and Nematostella, which can rebuild entire bodies from small fragments, to planarian flatworms, annelids, echinoderms, fish, amphibians and mammals. In nearly every regenerative model examined, pharmacological or genetic suppression of ROS production—most often by blocking the NADPH oxidase enzymes, or NOXes, that generate superoxide at the wound—impairs regeneration. Conversely, exogenous hydrogen peroxide can, in some systems, partially rescue defective regenerative responses. The consistency of this pattern across such distantly related animals raises the tantalizing possibility that ROS signaling is not a collection of independent evolutionary accidents but a deeply rooted, possibly ancestral, component of the regeneration program.

The review is careful, however, to emphasize that conserved does not mean uniform. The regulatory roles and modes of action of ROS vary considerably among species, tissues and regenerative contexts. In some animals, ROS act primarily in the earliest wound-healing phase, recruiting immune cells and initiating proliferation; in others, oxidative signals persist into blastema formation, the mass of progenitor cells from which the new structure grows. The downstream targets differ as well: ROS have been implicated in activating Wnt, FGF, ERK and JNK signaling pathways, in modulating apoptosis, and in shaping the extracellular matrix, but the specific wiring differs from one organism to the next. This variability, the authors argue, is precisely why continued comparative study is essential. Only by mapping ROS involvement across many species can researchers distinguish genuinely common mechanisms from species-specific embellishments.

This comparative logic carries the review into deeper evolutionary waters. The evolutionary history of regeneration remains one of the great unresolved puzzles in biology. Why can a salamander regrow an entire limb while a mouse cannot? Why do some annelids regenerate their whole posterior body axis while closely related species fail at the same task? Two competing frameworks dominate the field: regeneration as an ancestral capacity repeatedly lost in lineages that traded it for other advantages, or regeneration as a trait independently gained, assembled from pre-existing wound-healing and developmental machinery. The authors argue that ROS data can inform this debate. If ROS signaling sits at the base of regenerative responses across the animal tree, it may represent an ancient, conserved layer of the process—one that lineages with poor regenerative abilities have not necessarily lost, but perhaps fail to deploy correctly.

That reframing has direct therapeutic implications, and it is here that the review makes its most forward-looking argument. Humans regenerate well in the liver, moderately in skin and bone, and hardly at all in the heart, spinal cord and limbs. If ROS signaling is a conserved trigger of regenerative programs, then modulating redox state could offer a lever to reactivate latent regenerative capacity in poorly regenerating human tissues. The concept is not fanciful. Studies in zebrafish and axolotl have shown that adjusting ROS levels can influence heart regeneration and appendage regrowth, and redox-sensitive pathways such as ERK and Wnt are already major targets of regenerative medicine research. The review suggests that a rigorous understanding of when, where and at what concentration ROS act could enable precisely timed redox interventions—boosting regeneration without tipping tissues into the oxidative damage that fuels fibrosis, inflammation and cancer.

The authors are equally candid about the obstacles. ROS are fleeting, highly reactive and difficult to measure with spatial and temporal precision, and many of the tools used to manipulate them—broad-spectrum antioxidants, generic NOX inhibitors—are blunt instruments with off-target effects. To address this, the review includes a supplementary compendium of the functional tools available to modulate ROS production in regeneration studies, cataloguing the main pharmacological inhibitors and activators as well as the principal targets for RNA interference, morpholino and knockout approaches. Standardizing and refining this toolkit, the authors contend, is a prerequisite for the field’s maturation. Without it, discrepancies between studies may reflect technical artifacts rather than genuine biological differences, muddying the comparative analyses on which evolutionary conclusions depend.

The review also identifies major knowledge gaps that will shape the next decade of work. The precise molecular targets of ROS during regeneration remain incompletely defined in most models; the dose, duration and gradients of oxidative signals at wounds are poorly quantified; and the interplay between ROS and other injury-induced signals—calcium fluxes, bioelectric gradients, mechanical forces and immune-derived cytokines—is only beginning to be explored. Another open question is whether ROS participate in the establishment of positional memory, the information that tells a regenerating blastema whether to build a hand, a tail or a head. Answering these questions will require combining live redox biosensors, genetic models and comparative approaches across species that span the breadth of regenerative ability, from master regenerators to refractory ones.

What emerges from the synthesis is a view of regeneration as a redox-gated process whose ancient logic may still be latent within our own cells. The authors, based at institutions including Université Paris Cité, Université Côte d’Azur, the University of Manchester, Sorbonne Université and École Normale Supérieure, argue that studying ROS across metazoan diversity serves a dual purpose: it illuminates how regeneration evolved, and it reveals why some species, including our own, regenerate poorly. Both lines of inquiry converge on the same practical prize—new strategies in regenerative medicine grounded in evolutionary insight rather than trial and error. If the oxidizing burst that follows injury truly is a conserved call to rebuild, then learning to read, and perhaps to amplify, that ancient signal could one day help human tissues do what salamanders have done for millions of years: grow back.

Subject of Research: The role of reactive oxygen species signaling in animal regeneration and its evolutionary and therapeutic implications

Article Title: Understanding ROS signaling and evolution during animal regeneration offers promising opportunities for novel therapeutic approaches

Article References: Vullien, A., John, J., Rampon, C., Amaya, E., Röttinger, E., & Gazave, E. (2026). Understanding ROS signaling and evolution during animal regeneration offers promising opportunities for novel therapeutic approaches. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06392-x

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06392-x

Keywords: reactive oxygen species, ROS signaling, regeneration, regenerative medicine, oxidative eustress, NADPH oxidase, evolutionary developmental biology, blastema, wound healing, redox biology, hydrogen peroxide, comparative biology