The research focused on the Bama miniature pig, a small breed from Guangxi in southern China prized both for its excellent meat quality and its growing role as a biomedical model for human research. The team collected samples from two anatomically distinct muscles at six time points: embryonic days 57, 73, and 90, and postnatal days 1, 28, and 120. The longissimus dorsi, a back muscle dominated by glycolytic type IIB fibers, represents the fast-twitch archetype, while the semitendinosus, rich in oxidative type I fibers, embodies the slow-twitch phenotype. This dual-region, dual-time design allowed the researchers to separate the effects of anatomy from the effects of developmental time—a distinction that many earlier studies, which sampled only single muscles or single stages, could not make.

Technically, the proteomic work was ambitious. The team employed non-targeted data-independent acquisition mass spectrometry, or nDIA, applied for the first time to porcine embryonic skeletal muscle fibers. Using an Orbitrap Astral mass spectrometer with 300 DIA windows and high-resolution scanning, they identified an average of 6,118 proteins per sample, with a range spanning roughly 3,500 to 7,400. The transcriptomic side relied on Illumina NovaSeq 6000 sequencing, capturing an average of 13,354 genes per sample. Together, these datasets covered the vast majority of the expressed muscle proteome and transcriptome, giving the researchers an unusually complete view of how gene activity and protein abundance change in parallel—and, crucially, where they diverge.

The most striking pattern to emerge was temporal rather than spatial. Across developmental stages, the researchers identified 3,509 differentially abundant proteins, dwarfing the 272 proteins that differed between the two muscle regions at any given stage. Principal component analysis showed that fetal samples from E57 through E90 clustered tightly together, with correlation coefficients between adjacent fetal stages reaching 0.86. But after birth, the samples separated sharply along the developmental timeline, and the correlation between E90 and P1 dropped to just 0.59—the lowest of any adjacent pair. Birth, in other words, marks a molecular discontinuity, a wholesale reprogramming of the muscle proteome that no other transition in the study approached in magnitude.

Within that postnatal reprogramming, one window stood out. Between postnatal days 1 and 28, the semitendinosus gained more newly expressed proteins than the longissimus dorsi, and the two regions showed significant differences in both protein abundance and the biological processes those proteins supported. A heatmap of mitochondrial respiratory complex proteins revealed that regional differences in oxidative machinery first appeared at P28 and reached their peak at P120. Because oxidative fibers carry far more mitochondrial content than glycolytic fibers, this divergence in mitochondrial protein abundance is a direct molecular signature of the slow-versus-fast fiber split. The finding aligns with older histological work from 1972 showing that pig oxidative and glycolytic fibers become distinguishable between 21 and 28 days after birth—but the new study supplies the protein-level detail that histology alone could never provide.

The integrated analysis also exposed a deep layer of post-transcriptional regulation. Classifying genes by how their RNA and protein levels changed together, the researchers found that more than 90 percent fell into categories showing minimal or discordant changes between the two levels. Most tellingly, the proportion of Type 2 genes—those with substantial protein-level changes but minimal RNA-level changes—jumped from under 10 percent during fetal stages to 12.8 percent at P1, 23 percent at P28, and 27.7 percent at P120. At P28, these Type 2 genes were enriched in ribosome biogenesis, lysosome function, and basal transcription factors, and gene set enrichment analysis linked them to fatty acid metabolism, a pathway known to run at higher activity in slow fibers. At P120, Type 5 genes, whose RNA and protein levels move in opposite directions, were enriched in the mTOR signaling pathway and lipoic acid metabolism. The message is clear: RNA sequencing alone would miss much of what actually drives muscle fiber specialization.

From the protein domain analysis came the study’s headline discovery. The serine/threonine kinase domain S_TKc was enriched in specific abundance trends in both muscles, but the proteins carrying it showed region-specific temporal patterns. One of these, NEK3—Never In Mitosis Gene A-Related Kinase 3—appeared as a differentially abundant protein between the two muscles at P1 with a striking log2 fold change exceeding 10, yet its RNA levels remained identical between regions throughout development. That discrepancy pointed to post-transcriptional control, and it is precisely the kind of regulatory mechanism that only a combined proteomic-transcriptomic approach can catch. The team used AlphaFold3 to model NEK3’s structure, then moved to the laboratory to test its function.

The functional experiments delivered a consistent verdict. When the researchers overexpressed NEK3 in mouse C2C12 myoblasts, MYHC expression dropped significantly, confirmed by both immunofluorescence and quantitative PCR. Western blotting showed that NEK3 overexpression suppressed MYH4, a fast-twitch fiber marker, while boosting MYH7 and PGC-1α, both hallmarks of slow oxidative fibers. The team then repeated the experiments in porcine embryonic muscle progenitor cells isolated from Bama pigs at 35 days post-coitum—a more physiologically relevant system—and observed the same pattern: fewer myotubes formed, and fast-twitch markers declined. NEK3, in short, acts as a conserved negative regulator of fast-twitch muscle fiber differentiation, and its transient, protein-only appearance at P1 suggests it helps orchestrate the fiber-type decisions made in the critical days after birth.

A second regulator, NCOA2, added another layer of nuance. This nuclear receptor coactivator, known to promote myogenic differentiation through the MEF2C pathway, showed distinct temporal patterns in the two muscles. In the fast-twitch longissimus dorsi, NCOA2 abundance began declining at E73 and vanished by P28; in the slow-twitch semitendinosus, the decline started later, at E90, and did not reach zero until P120. Because most fetal pig muscle fibers start life with slow-twitch characteristics, the researchers interpret NCOA2 as a molecular brake on the slow-to-fast transition: its early disappearance in the longissimus dorsi licenses that muscle to become fast, while its persistence in the semitendinosus preserves slow fiber identity deep into maturity.

Finally, the team widened the lens across species. Comparing 1,869 single-copy orthologous genes among pig, human, and mouse skeletal muscle at weaning-equivalent stages—postnatal day 28 in pigs, day 20 in mice, and 7 months in humans—they found that pig-specific high-expression clusters were enriched in skeletal muscle organ development, circulatory system development, and heart development, while pig-specific low-expression clusters involved autophagy and insulin receptor signaling. Intriguingly, genes tied to lung development were also elevated in pigs at this stage, hinting at a coordinated developmental program in which maturing respiratory muscles provide the mechanical forces that drive lung maturation. For pig farmers, the P28 window coincides with weaning, the most economically sensitive moment in production, suggesting that management strategies protecting muscle development during this period could pay dividends in both meat quality and animal health. For biomedical researchers, the study offers a molecular roadmap of muscle maturation in one of the most important animal models of human physiology—and a reminder that the proteins, not just the genes, tell the fuller story.

Subject of Research: Dynamic changes in muscle fiber types across developmental stages of porcine skeletal muscle, analyzed by integrated proteomics and transcriptomics

Article Title: Integrated proteomics and transcriptomics analysis of dynamic changes in muscle fiber types in different regions of porcine skeletal muscle

Article References: Feng, Z., Wang, X., Zhou, Q., Liu, Y., Xu, R., Liang, Z., Zhang, C., Liu, X., Zhao, Y., Chen, Y., & Mo, D. (2025). Integrated proteomics and transcriptomics analysis of dynamic changes in muscle fiber types in different regions of porcine skeletal muscle. Advanced Biotechnology, 3(4), Article 29. https://doi.org/10.1007/s44307-025-00080-w

Image Credits: AI Generated

DOI: 10.1007/s44307-025-00080-w

Keywords: skeletal muscle, muscle fiber types, proteomics, transcriptomics, Bama miniature pig, NEK3, NCOA2, mitochondria, myogenesis, meat quality, data-independent acquisition, postnatal development

The research, led by Gaizhen Li and Dong Liu of Xiamen University together with colleagues including corresponding authors Haibin Wang, Haili Bao and Shuangbo Kong, focuses on METTL3, the core writer enzyme of N6-methyladenosine, or m6A, the most abundant internal modification in eukaryotic messenger RNA. By depositing methyl groups on adenosine bases, METTL3 influences how transcripts are processed, translated and degraded, effectively acting as a post-transcriptional tuning dial for gene expression. While m6A is known to govern stem cell fate and organogenesis in several systems, its role in the postnatal uterus had remained unexplored.

To map the normal course of epithelial specification, the team charted the transcriptional and chromatin landscape of uterine epithelial cells during early postnatal life. Their analysis showed that luminal epithelial specification is not a simple switch but a dynamic transition: cells first pass through a proliferative phase and then shift into a state of metabolic activation. This shift is orchestrated by coordinated networks of transcription factors acting on chromatin regions that become progressively more accessible, allowing the cell to lock in its luminal identity. From these data, the researchers defined a set of genes specifically associated with luminal epithelial specification, providing a molecular reference point for what a properly specified luminal cell should look like.

The decisive experiment came from genetics. Using a uterine-specific Mettl3 knockout mouse model, the researchers deleted METTL3 from the developing uterus and watched what happened to epithelial specification. The result was striking: without METTL3, luminal epithelial specification broke down. Instead of committing cleanly to the luminal lineage, epithelial cells emerged in a hybrid state, co-expressing markers of both luminal and glandular epithelium. The developing tissue, in other words, could no longer tell its two epithelial lineages apart, producing cells that belonged fully to neither.

The consequences of this failed specification extended well beyond the developmental window itself. Adult mice whose uteri had lacked METTL3 during early postnatal life showed a predisposition to hormone-driven glandular hyperplasia, an abnormal proliferation of glandular tissue in response to ovarian hormones. This finding carries a provocative implication: errors made in a brief postnatal period of lineage specification can lay the groundwork for uterine pathology in adulthood, suggesting that the developmental window during which luminal epithelium matures is a critical period whose disruption may echo for a lifetime.

Mechanistically, the study disentangled two ways in which METTL3 safeguards proper specification. First, the enzyme helps regulate the expression levels of the genes that define luminal epithelial identity, ensuring that the specification program is executed at the right intensity. Second, and more specifically, METTL3 stabilizes the transcripts of key transcription factors, including Etv5, a member of the ETS family known for its roles in epithelial growth and differentiation. By methylating these transcripts, METTL3 protects them from premature decay, keeping the transcription factor circuitry supplied with the raw material it needs to drive the luminal program forward. When METTL3 is absent, these regulatory transcripts dwindle, the circuitry falters, and the hybrid luminal-glandular phenotype emerges.

The work places RNA modification squarely within the framework of developmental lineage decisions. Classical models of cell fate specification emphasize transcription factors and chromatin remodeling as the primary arbiters of identity, and the new data support that view, showing coordinated transcription factor networks and changing chromatin accessibility during specification. But the findings add a crucial post-transcriptional layer: the same genetic program can be derailed if the RNA messages encoding its regulators are not chemically stabilized. In this sense, m6A modification functions less as an independent decision-maker and more as an essential quality-control system that keeps the specification machinery running at full capacity.

For reproductive biology, the study fills a significant gap. The formation of glandular epithelium from undifferentiated luminal epithelium, followed by the precise maturation of both lineages, is essential for establishing uterine architecture and, ultimately, female fertility. Glands of the endometrium are central to implantation and early pregnancy, and defects in uterine epithelial development are implicated in infertility and endometrial disease. By identifying METTL3-dependent m6A modification as indispensable for luminal epithelial specification, the researchers have pinpointed a molecular node whose dysfunction could plausibly contribute to disorders of uterine development and hormone responsiveness.

The mouse model used in the study also offers a platform for future investigation. Because the knockout was restricted to the uterus, the phenotype can be attributed directly to the uterine epithelium rather than to systemic effects of METTL3 loss, an important consideration given the enzyme’s broad roles throughout the body. The authors acknowledge contributions of Pgr-Cre and Mettl3-flox mouse lines from Francesco DeMayo of the National Institute of Environmental Health Sciences and Minghan Tong of the Center for Excellence in Molecular Cell Science, CAS, tools that made the tissue-specific deletion possible. The work was supported by the National Key Research and Development Program of China, the National Natural Science Foundation of China and the Natural Science Foundation of Fujian Province.

Looking ahead, the study raises questions that extend beyond the uterus. If m6A modification is required for lineage specification in this organ, similar requirements may operate in other epithelial systems that mature postnatally, from the gut to the mammary gland. The identification of a defined set of luminal specification-associated genes, together with the demonstration that transcript stabilization of factors such as Etv5 underpins the process, gives researchers concrete molecular handles for probing those questions. For now, the message from Xiamen is clear: the chemical editing of RNA is not a footnote to development but a load-bearing pillar, and the architecture of the adult uterus rests on it.

Subject of Research: The role of METTL3-mediated m6A RNA modification in postnatal uterine luminal epithelial lineage specification

Article Title: METTL3-mediated RNA m6A modification orchestrates postnatal uterine epithelial specification

Article References: Li, G., Liu, D., Liu, J., Ni, Y., Deng, N., Wang, L., Huang, L., Tang, Y., Hao, J., Wang, M., Zhang, Y., Deng, W., Wang, H., Bao, H., & Kong, S. (2026). METTL3-mediated RNA m6A modification orchestrates postnatal uterine epithelial specification. Cellular and Molecular Life Sciences. https://doi.org/10.1007/s00018-026-06462-0

Image Credits: AI Generated

DOI: 10.1007/s00018-026-06462-0

Keywords: METTL3, m6A modification, uterine development, luminal epithelium, glandular epithelium, lineage specification, Etv5, transcription factors, postnatal development, epigenetics, reproductive biology, glandular hyperplasia

Perineuronal nets, or PNNs, are specialized matrix structures composed of chondroitin sulfate proteoglycans, hyaluronan, and link proteins that encase the cell bodies and proximal dendrites of certain classes of neurons, most prominently fast-spiking parvalbumin interneurons. These nets are far more than passive scaffolding. They are thought to regulate the balance of excitation and inhibition in neural circuits and to govern the closure of critical periods of plasticity, the windows during which the brain is exquisitely malleable. When that balance is disturbed, the consequences can be profound: altered excitation-inhibition ratios and disrupted PNN formation have both been implicated in neurodevelopmental disorders, including autism spectrum disorder, a condition diagnosed substantially more often in biologically male children and adults. Understanding when and how PNNs normally appear, therefore, is not merely an exercise in descriptive neuroanatomy; it could illuminate when the developing brain is most vulnerable to insult.

Yet most of what scientists know about PNNs comes from studies of adolescent and adult animals, long after the nets have consolidated. Very little research has charted the typical, day-by-day emergence of PNNs and the parvalbumin interneurons they envelop during the earlier stretches of development. The research team, led by Abigail W. Hamilton and Susan L. Zup, set out to fill that gap by building a precise timeline of PNN onset in juvenile Sprague Dawley rats across a narrow but crucial developmental span: postnatal days 14, 16, 18, and 22. They focused on the dorsal hippocampus, a region central to learning, memory, and stress regulation, examining five distinct subregions: the subiculum, cornu ammonis 1 (CA1), CA2, CA3, and the dentate gyrus.

The methodology was straightforward but demanding in its precision. Rats at each of the four ages were transcardially perfused, and their brains were sectioned and processed for immunofluorescence staining targeting both perineuronal nets and parvalbumin interneurons. By labeling these two features simultaneously, the researchers could count net-bearing neurons in each hippocampal subregion at each time point and, crucially, compare counts between males and females. This fine-grained sampling at two-day intervals allowed the team to capture developmental dynamics that coarser, week-long sampling intervals might have smoothed away entirely.

The results upended the intuitive assumption that PNN numbers climb steadily as the juvenile brain matures. Instead, the researchers found that PNN counts fluctuated across the p14 to p22 window in a consistent pattern of decline followed by rebound, rather than increasing linearly. Remarkably, male and female rats followed the same general trajectory, but on shifted schedules. Female rats showed a dip in perineuronal net number at postnatal day 16 before the counts rebounded, whereas males exhibited a similarly steep decrease two days later, at postnatal day 18, before their own recovery. In other words, the female developmental program appeared to run ahead of the male one, completing the same sequence of net loss and net gain several days earlier.

Across subregions of the hippocampus, the study also documented a broader sex difference: males generally had fewer perineuronal nets than females. This asymmetry is particularly intriguing in light of the clinical epidemiology of autism spectrum disorder, which is more prevalent in biologically male children and adults. Because PNNs help regulate the excitation-inhibition balance whose disruption is associated with the disorder, the authors suggest that differences in the timing and density of net formation between the sexes could contribute to differential vulnerability. A male brain whose PNN maturation lags behind a female’s may spend a longer stretch of development in a state where its inhibitory circuitry and plasticity controls are still in flux, opening more or longer windows during which environmental, genetic, or biochemical insults could derail typical trajectories.

The fluctuations themselves carry implications for how neuroscientists should think about early brain development. If PNN numbers can drop sharply within a matter of days and then rebound, the developing hippocampus cannot be viewed as a structure steadily locking in its inhibitory architecture. Instead, it appears to pass through alternating phases in which nets are pruned and re-established, potentially reflecting active remodeling of parvalbumin interneuron circuitry during the juvenile period. Each phase of net reduction may correspond to a period of heightened plasticity, when circuits are more open to modification, and each phase of net re-accumulation to a period in which those modifications are being consolidated. Sex differences in the timing of these phases would mean that males and females are not equally susceptible to the same disruption at the same chronological age.

The study’s authors emphasize that these data point to windows of both increased and decreased vulnerability to neurons and neuronal circuitry during early neurodevelopment, windows that are specific to sex. For researchers modeling neurodevelopmental disorders in animals, the message is that the choice of developmental time point is not neutral. A postnatal day 16 female and a postnatal day 18 male may occupy comparable positions in their respective PNN trajectories, while a male and female of the same chronological age may be at entirely different stages. Experimental interventions, environmental manipulations, or pharmacological challenges delivered on identical schedules could therefore produce systematically different outcomes in the two sexes, a confound that precise developmental timelines like this one can now help investigators control for.

More broadly, the work adds to the growing recognition that sex differences are not peripheral curiosities in neuroscience but fundamental features of brain development that deserve systematic study from the earliest ages. By mapping the fluctuating emergence of perineuronal nets and their parvalbumin interneuron partners across the dorsal hippocampus, the University of Massachusetts Boston team has provided a reference framework against which future studies of atypical development can be measured. The research was funded by the University of Massachusetts Boston’s Program Development Grant and College of Liberal Arts Research Funds, and all experiments were approved by the institution’s Institutional Animal Care and Use Committee. As the field continues to probe the developmental roots of conditions like autism spectrum disorder, this sex- and age-resolved atlas of early hippocampal PNN development offers both a caution against assuming steady linear maturation and a promising map of the moments when the juvenile brain may be most, or least, open to lasting change.

Beyond the immediate findings, the study sits within a broader methodological shift in neuroscience. For decades, preclinical research relied disproportionately on male animals, partly on the assumption that cyclic hormonal variation in females would introduce unwanted variability. That assumption has been repeatedly challenged, and funding agencies now routinely require attention to sex as a biological variable. The present work illustrates why such policies matter: had the investigators examined only one sex, or only a single developmental time point, the fluctuating, sex-shifted trajectory of perineuronal net development would have been invisible. A study sampling at postnatal day 16 alone, for instance, would have concluded that females show reduced net density relative to earlier ages, while a day 18 sample would have suggested the same for males, with neither result revealing the underlying shared pattern.

The choice of the dorsal hippocampus also carries significance for interpretation. This region receives extensive attention in research on learning, memory consolidation, and the physiological stress response, and its parvalbumin interneuron population is known to mature gradually across the juvenile period. Parvalbumin cells are fast-spiking inhibitory neurons that depend on precise excitatory input and on metabolic and structural support from the extracellular matrix that surrounds them. Perineuronal nets are believed to stabilize the synapses formed on these cells and to contribute to the maturation of their characteristic rapid firing properties, so fluctuations in net number during the juvenile window may reflect ongoing reorganization of inhibitory microcircuitry rather than simple cell loss or gain.

It is also worth noting what the study does and does not establish. The work documents correlations between age, sex, and net abundance in a typical laboratory strain; it does not demonstrate a causal link between perineuronal net timing and any disorder. Autism spectrum disorder in humans involves many genetic and environmental influences, and rodent hippocampal development, while homologous in broad outline, cannot be mapped directly onto human clinical outcomes. What the data provide is a normative reference: a detailed baseline against which future studies of genetically modified animals, early-life stress models, or environmental exposures can be compared. Such baselines are essential for detecting whether an experimental manipulation accelerates, delays, or flattens the normal developmental curve in one sex but not the other.

The article itself was published as open access under a Creative Commons Attribution license, making the full dataset and methods available to any laboratory without subscription barriers. The version released in early September 2026 is a citable accepted manuscript carrying a permanent digital object identifier, with a final version of record to follow after routine production edits. For a field increasingly attentive to reproducibility, the combination of fine-grained age sampling, dual immunofluorescence labeling, and sex-balanced design offers a template for how descriptive developmental neuroanatomy can be made both rigorous and broadly reusable.

Subject of Research: Sex differences in the developmental timing of perineuronal nets in the rat hippocampus

Article Title: Sex and age impact the developmental trajectory of perineuronal net number in the rat dorsal hippocampus

Article References: Hamilton, A. W., Pritchard, E. K., Hunter III, R. G., & Zup, S. L. (2026). Sex and age impact the developmental trajectory of perineuronal net number in the rat dorsal hippocampus. Biology of Sex Differences. https://doi.org/10.1186/s13293-026-00961-2

Image Credits: AI Generated

DOI: 10.1186/s13293-026-00961-2

Keywords: perineuronal nets, hippocampus, sex differences, neurodevelopment, parvalbumin interneurons, autism spectrum disorder, rats, excitation-inhibition balance, critical periods, postnatal development, extracellular matrix, plasticity