For much of the twentieth century, mammalian development was viewed primarily as a one-way journey. In the classic image proposed by developmental biologist Conrad Waddington in 1957, a ball rolls down a mountainous landscape, leaving the high plateau of developmental potential and settling into increasingly specialized valleys. Embryonic stem cells could differentiate into restricted lineages, but a mature cell was thought to have largely lost the ability to climb back up the landscape. That model captured the stability of cell identity, but it did not fully describe its potential reversibility. The conceptual breakthrough came in 2006, when Shinya Yamanaka and colleagues reported that four transcription factors could convert mouse fibroblasts into cells with properties resembling embryonic stem cells.

The factors—Oct3/4, Sox2, Klf4, and c-Myc, commonly abbreviated as OSKM—act as molecular regulators of gene expression rather than as structural components of the cell. When introduced into differentiated fibroblasts, they reorganize the gene-regulatory circuitry that maintains the mature state. They also reshape chromatin, the DNA-protein material that determines which genes are accessible for transcription. Over time, genes associated with fibroblast identity are silenced while networks linked to self-renewal and pluripotency become active. The process is inefficient and asynchronous: only a small fraction of treated cells successfully complete the transition, and individual cells may pass through different intermediate states before reaching an induced pluripotent state.

This inefficiency revealed that reprogramming is not a simple molecular reset controlled by four independent switches. Instead, it is a competition between stable cellular programs, epigenetic barriers, metabolic changes, and stochastic events. Some cells fail to activate the core pluripotency network, while others enter incomplete or abnormal states. DNA methylation patterns must be extensively remodeled, enhancer activity must be reorganized, and the cell’s metabolism must shift as it moves from a mature somatic program toward a stem-cell-like condition. These changes helped establish a broader principle: differentiation and reprogramming are opposing movements across a dynamic developmental landscape. Understanding how a cell enters, maintains, or exits pluripotency can therefore illuminate both normal development and the mechanisms used to reverse it.

The underlying idea that differentiated cells retain latent developmental potential was demonstrated decades earlier by John Gurdon. In experiments published in 1962, Gurdon transferred the nucleus of a differentiated tadpole intestinal cell into an enucleated frog egg. The reconstructed embryo could develop into a normal tadpole, showing that the specialized nucleus still contained the genetic information required to build an organism. Nuclear transfer, however, depended on the complex environment of an egg cell. Yamanaka’s work was transformative because it showed that mammalian cell identity could be altered using a small set of defined transcription factors alone. The discovery converted a question once associated with embryology into a practical technology that could be reproduced in laboratories around the world.

The next year, researchers generated induced pluripotent stem cells from adult human fibroblasts. Human iPSCs gave scientists a way to create genetically relevant, patient-specific cell lines without relying on embryos. In principle, a skin or blood sample can be reprogrammed and then differentiated into neurons, heart muscle cells, liver cells, retinal cells, or other specialized populations. These cells can carry disease-associated genetic variants, allowing researchers to study pathological mechanisms in a dish. They can also be used to test candidate medicines on human-derived tissue, potentially revealing toxicities or treatment responses that conventional animal models do not predict reliably. Yet the technology carries important technical challenges, including genomic instability, residual epigenetic memory, variation between cell lines, incomplete differentiation, and the risk that undifferentiated cells could form tumors after transplantation.

The clinical ambitions of the field are now moving beyond theory. Early-stage trials have tested cell products derived from pluripotent stem cells, including retinal pigment epithelium intended to treat macular degeneration and dopaminergic neurons designed to replace cells lost in Parkinson’s disease. The goal is not simply to place stem cells into damaged tissue, but to manufacture a highly characterized population with the correct identity, maturity, function, and safety profile. Researchers must establish that the cells do not contain dangerous mutations, that unwanted cell types have been removed, and that the transplanted population behaves predictably over time. Manufacturing at clinical scale also requires tightly controlled culture conditions, standardized quality testing, and long-term monitoring of patients.

The field is simultaneously expanding in directions that challenge the original definition of reprogramming. Partial reprogramming, for example, exposes cells to reprogramming factors for a limited period rather than pushing them all the way to pluripotency. In experimental systems, this approach has been used to reverse some molecular features associated with aging while preserving aspects of the cell’s original identity. The strategy is technically delicate: too little reprogramming may produce minimal benefit, while too much can erase cell identity or promote abnormal growth. Chemical reprogramming offers another alternative. Instead of delivering transcription-factor genes, researchers use combinations of small molecules to alter signaling pathways, chromatin states, metabolism, and transcriptional regulation. This may improve control over timing and reduce some risks associated with genetic delivery, although efficiency, reproducibility, and safety remain major obstacles.

New measurement technologies are making these transitions visible at unprecedented resolution. Single-cell RNA sequencing can track gene-expression changes in individual cells rather than averaging signals across an entire culture. Single-cell epigenomic methods reveal how DNA methylation, histone modifications, and chromatin accessibility change during fate conversion. Spatial transcriptomics adds a geographic dimension, showing where distinct cell states occur within tissues or organoid structures. Advanced imaging can follow cell division, morphology, and lineage behavior in real time, while computational models reconstruct gene-regulatory networks and identify the molecular events that separate successful reprogramming from failure. Together, these approaches are transforming cellular identity from a static label into a measurable trajectory through molecular and physical states.

Another rapidly developing frontier is the construction of stem-cell-based embryo and tissue models. Organoids can reproduce selected features of organs, including aspects of tissue architecture, physiology, and disease. More integrated models attempt to recreate interactions among multiple lineages during early development, offering a way to investigate processes that are difficult or impossible to observe directly in embryos. These systems can reveal how signaling pathways, mechanical forces, cell migration, chromatin organization, and metabolism cooperate to produce organized tissues. They also raise difficult ethical and regulatory questions, particularly as models become more complex and begin to resemble aspects of embryonic development more closely. The anniversary collection announced by BMC Biology is intended to bring together research addressing these biological, technological, and ethical challenges.

Twenty years after OSKM first overturned the idea that development is irreversible, the central question has become more precise: not merely whether a cell can change identity, but how that change is initiated, stabilized, coordinated across a population, and safely directed toward a therapeutic outcome. Scientists are now examining developmental plasticity in diverse species, the spatial organization of lineage decisions, the molecular logic of tissue patterning, and the systems-level principles that integrate gene regulation with signaling, metabolism, and mechanics. The history of iPSCs began with a compact set of transcription factors, but its future will depend on far more than four genes. It will require predictive models of cell fate, reliable methods for producing mature functional cells, and rigorous safeguards that convert cellular plasticity into medicine without sacrificing biological control.

Subject of Research: Induced pluripotent stem cells, cellular reprogramming, pluripotency, differentiation, developmental plasticity, stem-cell-based models, and regenerative medicine

Article Title: Pluripotency, differentiation, and reprogramming: 20 years of induced pluripotent stem cells

Article References: Takahashi and Yamanaka, Cell (2006), DOI: 10.1016/j.cell.2006.07.024; Gurdon, Journal of Embryology and Experimental Morphology (1962); Takahashi et al., Cell (2007), DOI: 10.1016/j.cell.2007.11.019; Yu et al., Science (2007), DOI: 10.1126/science.1151526; Shi et al., Nature Reviews Drug Discovery (2017), DOI: 10.1038/nrd.2016.245; Mandai et al., New England Journal of Medicine (2017), DOI: 10.1056/NEJMoa1608368; Sawamoto et al., Nature (2025), DOI: 10.1038/s41586-025-08700-0; Ocampo et al., Cell (2016), DOI: 10.1016/j.cell.2016.11.052; Guan et al., Nature (2022), DOI: 10.1038/s41586-022-04593-5; Eiraku et al., Nature (2011), DOI: 10.1038/nature09941

Image Credits: AI Generated

DOI: 10.1186/s12915-026-02712-6

Keywords: induced pluripotent stem cells, iPSCs, pluripotency, cellular reprogramming, OSKM, Yamanaka factors, differentiation, stem cell biology, regenerative medicine, organoids, embryo models, single-cell multi-omics, spatial transcriptomics, partial reprogramming, chemical reprogramming

At the heart of this research is a class of retrotransposons known as LTR5Hs, remnants of ancient viral elements integrated into the human genome. The focus was to disentangle whether the regulatory effects observed in the human epiblast are truly dependent on specific LTR5Hs DNA sequences or merely an artifact of gene silencing techniques. By employing CRISPR-mediated deletions of six distinct LTR5Hs elements near genes integral to epiblast function and pluripotency, the investigators aimed to establish a direct causative link.

In a meticulous approach, human naive pluripotent stem cells (hnPSCs) were engineered to carry precise deletions—either homozygous or heterozygous—in individual LTR5Hs elements. These elements are located in cis landscapes next to pivotal developmental genes such as SUSD2, marking naive pluripotency; ZNF729, associated with naive and formative pluripotency; and BARD1, a BRCA1 partner vital for embryonic development. The careful generation of multiple independent clonal lines allowed for robust comparisons against wild-type controls.

Quantitative PCR analyses revealed a consistent downregulation of candidate genes upon LTR5Hs deletions, establishing the enhancer-like functionality of these retrotransposon-derived sequences. Intriguingly, certain deletions influenced multiple adjacent genes, such as SUSD2/CABIN1 and SERPINB9/SERPINB6, while some target loci remained unaffected in cis, indicative of remarkable selectivity in gene regulatory mechanisms. This specificity alludes to a sophisticated enhancer landscape sculpted by LTR5Hs elements.

Of particular interest was the inability to recover homozygous deletions of the SERPINB9-associated LTR5Hs, hinting at an essential developmental role or viability effect. Additionally, clones lacking the LTR5Hs element near ZNF729 exhibited reduced proliferation rates, underscoring the functional relevance of this regulatory region in cell growth dynamics. Yet, morphologically, these deletions did not result in overt changes, emphasizing subtle molecular control rather than gross cellular phenotype disruptions.

The versatile enhancer attributes of LTR5Hs were further corroborated by their capacity to activate promoters located at variable genomic distances and in both orientations relative to the target gene. These features resonate with classical enhancer paradigms, showcasing evolutionary innovation by co-opting retroviral sequences for developmental gene regulation. Such hominoid-specific enhancers appear to underpin the unique regulatory architecture characterizing human embryogenesis.

Cross-species analyses provided compelling evidence of evolutionary divergence. LTR5Hs elements are exclusive to humans; their regulatory targets, such as ZNF729, exhibit conserved gene sequences but lack comparable expression in non-human primates like rhesus monkeys. This distinction aligns with the presence of LTR5Hs in the human genome and absence in other mammals, underscoring the intertwined evolution of genetic elements and species-specific developmental processes.

Functionally, the deletion of the LTR5Hs adjacent to ZNF729 resulted in a profound impairment of blastoid formation—a three-dimensional in vitro model mimicking human blastocyst development. Rescue experiments, wherein ZNF729 was overexpressed in deletion lines, restored blastoid generation, illustrating a causative role for this enhancer-gene duo in early embryonic architecture. This model offers an unprecedented window into human pre-implantation development, impossible to study directly in vivo.

The study’s integration of molecular genetics, stem cell biology, and evolutionary genomics heralds a new era of understanding how ancient viral sequences have been repurposed as critical regulatory elements during human evolution. By harnessing CRISPR technologies and sophisticated in vitro models, researchers have delineated a human-specific enhancer landscape governing pluripotency and early developmental competence.

Importantly, the findings also open avenues for exploring how dysregulation of such enhancers might contribute to developmental disorders or impact regenerative medicine strategies. The unique regulatory control unveiled here challenges researchers to reconsider the roles of repetitive elements traditionally deemed “junk DNA,” proposing instead that they are vital contributors to human biology.

This research not only charts new territory in the understanding of gene regulation during human development but also underscores the complexity and ingenuity of genomic evolution. The enhancement of epiblast gene expression by LTR5Hs illustrates a sophisticated mechanism by which humans may have evolved unique embryonic features with implications for species-specific physiology.

Future directions include parsing the interplay between LTR5Hs enhancers and the broader epigenetic landscape, deciphering the mechanisms guiding their selective activation, and exploring their potential involvement in pathological states. Moreover, leveraging these insights could improve stem cell-based models and therapeutic approaches by aligning them with authentic human developmental pathways.

In summary, the identification of hominoid-specific retroviral enhancers that orchestrate vital gene networks marks a transformative leap in developmental biology. Through precise genomic manipulation and phenotypic assays, this work eloquently demonstrates that the genomic legacy of ancient viruses continues to shape what it means to be human, starting from the earliest stages of life.

Subject of Research: Human-specific LTR5Hs retrotransposons function as enhancers driving gene expression in the human epiblast during early development.

Article Title: A human-specific regulatory mechanism revealed in a pre-implantation model.

Article References: Fueyo, R., Wang, S., Crocker, O.J. et al. A human-specific regulatory mechanism revealed in a pre-implantation model. Nature (2025). https://doi.org/10.1038/s41586-025-09571-1

Image Credits: AI Generated

Prof. Meshorer’s election carries special resonance at a time when Israel’s scientific community continues to thrive amid considerable societal and geopolitical challenges. According to Prof. Tamir Sheafer, Rector of The Hebrew University, this recognition is not merely an individual accolade but a testament to the university’s dedication to scientific excellence and innovation. The election highlights the resilience and global reach of Hebrew University researchers, showcasing their ability to conduct impactful, cutting-edge science that transcends borders and politics.

The scientific heart of Prof. Meshorer’s research lies in unraveling the epigenetic mechanisms that govern chromatin structure and dynamics, particularly in embryonic stem cells. His laboratory explores how the plasticity of chromatin—the complex of DNA and proteins within the cell nucleus—regulates gene expression programs essential for stem cell pluripotency, differentiation pathways, and ultimately, cell fate decisions. This realm of biology is vital for understanding how a single genome can produce the diverse cell types required during development and tissue homeostasis.

Diving deeper into chromatin biology, Prof. Meshorer’s work elucidates the intricate relationship between histone modifications, DNA methylation, and nucleosome positioning, which together orchestrate the accessibility of genetic information for transcriptional machinery. By applying state-of-the-art genomic technologies, including single-cell epigenomics and chromatin conformation assays, his group maps dynamic changes in chromatin landscapes during neuronal differentiation and in stem cell models of neurodegenerative diseases. These insights are pivotal for uncovering how epigenetic regulation can go awry in pathological states.

One of the hallmarks of Prof. Meshorer’s contribution is the interdisciplinary approach combining molecular genetics, cell biology, and computational genomics. His lab’s discoveries on the maintenance of pluripotency via chromatin remodeling complexes offer compelling evidence of epigenetic flexibility as a cornerstone of stem cell biology. These molecular pathways hold significant promise for regenerative medicine, as modulating epigenetic states could enable controlled differentiation of stem cells into desired lineages, presenting therapeutic avenues for currently incurable neurological conditions.

Beyond classical epigenetics, Prof. Meshorer has notably co-pioneered the emerging field of paleo-epigenetics. By reconstructing DNA methylation patterns in archaic human genomes, including Neanderthals and Denisovans, his research provides unprecedented insight into evolutionary biology and the epigenetic basis of human adaptation. This innovative approach bridges modern molecular biology with anthropology, revealing how epigenetic modifications contributed to species-specific traits and evolutionary divergence.

Prof. Meshorer’s election to EMBO will enhance collaborative opportunities among the international life sciences community, fostering interdisciplinary research aimed at decoding complex biological systems. EMBO membership is awarded not only as a recognition of scientific excellence but also as an invitation to contribute actively to the advancement of molecular biology through joint initiatives, policy shaping, and mentoring young scientists worldwide.

In his own words, Prof. Meshorer expressed deep honor at joining EMBO, emphasizing that this recognition reflects both individual achievement and collective creativity borne from collaborative scientific environments. He anticipates engaging with EMBO’s mission to promote excellence and facilitate cross-border scientific interaction, which he views as essential for tackling the multifaceted challenges in biology and medicine.

The research paradigm championed by Prof. Meshorer addresses fundamental questions in developmental biology: How is genomic information dynamically regulated during cell state transitions? How do epigenetic landscapes sculpt cellular identity and function? His work significantly contributes to decoding the epigenetic language that mediates plasticity and stability within genomes, thus impacting fields ranging from neurobiology to regenerative therapeutics.

The translation of Prof. Meshorer’s findings into disease contexts is particularly impactful in neurodegenerative disorders, where epigenomic dysregulation may underlie pathological neuronal degeneration. By employing stem cell-derived neuronal models, his research elucidates molecular mechanisms that could be harnessed for interventions aiming to restore epigenetic balance and neuronal function, offering hope for new treatment strategies.

Moreover, Prof. Meshorer’s innovative use of high-resolution epigenetic profiling technologies sets benchmarks for future studies investigating chromatin dynamics. The refinement of these tools allows scientists to capture transient chromatin states and heterogeneous epigenetic landscapes at a single-cell level, thereby pushing forward our understanding of gene regulation in complex tissues and disease.

The Hebrew University lauds Prof. Meshorer’s achievement as emblematic of its enduring commitment to fostering world-class research that propels scientific frontiers. His election to EMBO not only honors his personal scientific journey but also shines a global spotlight on the vibrant life sciences ecosystem nurtured within Israeli academia.

As Prof. Meshorer steps into this new role within EMBO, the scientific community eagerly anticipates his continued contributions towards unraveling the epigenetic codes that govern development and disease. His work epitomizes the fusion of technical innovation and conceptual breakthroughs necessary to solve some of biology’s most challenging puzzles in the 21st century.

Subject of Research: Epigenetics, Chromatin Biology, Stem Cell Pluripotency, Neurodegenerative Diseases, Paleo-epigenetics

Article Title: Prof. Eran Meshorer Elected to EMBO for Groundbreaking Research in Epigenetics and Stem Cell Biology

News Publication Date: Information not provided

Web References: https://mediasvc.eurekalert.org/Api/v1/Multimedia/416529ae-d116-4492-adee-1c336ee69350/Rendition/low-res/Content/Public

Image Credits: Eviatar Klopstock

Keywords: Epigenetics, Chromatin, Stem cell research, Gene expression, Neurodegenerative diseases, Genome plasticity, Developmental biology