Pluripotent stem cells related to embryonic disc exhibit common self-renewal requirements in diverse livestock species

A Universal 6iL/E4 Culture System for Deriving and Maintaining Embryonic Stem Cells Across Mammalian Species

The derivation of authentic embryonic stem cells (ESCs) from diverse mammalian species offers valuable opportunities for advancing regenerative medicine, studying developmental biology, and enabling species conservation. Here, we report the development of a robust, serum-free culture system, termed 6iL/E4 that enables the derivation and long-term self-renewal of ESCs from multiple mammalian species, including mouse, rat, bovine, rabbit, and human. Using systematic signaling pathway analysis, we identified key regulators-including GSK3α, STAT3, PDGFR, BRAF, and LATS-critical for ESC maintenance across species. Additionally, inducible expression of KLF2 and NANOG enhances the naive pluripotency and chimeric potential of bovine ESCs. The E4 medium also supports stable ESC growth while minimizing lineage bias. These findings reveal conserved principles underlying ESC self-renewal across divergent mammalian species and provide a universal platform for cross-species stem cell research, disease modeling, and biotechnology applications.

In Brief

Wang et al. developed 6iL/E4, a serum-free system sustaining ESCs from mouse, rat, bovine, rabbit, and human. These findings reveal conserved fundamental mechanisms governing ESC self-renewal across diverse mammalian species.

Highlights

Developed 6iL/E4 system for ESC derivation across five mammalian species.PDGFR signaling inhibition as critical for ESC derivation across species.E4 medium improves ESC maintenance and avoids neural bias of traditional N2B27.Inducible KLF2/NANOG enhances naive pluripotency and chimera formation in bovine.

Wnt Inhibition Safeguards Porcine Embryonic Stem Cells From the Acquisition of Extraembryonic Endoderm Cell Fates

Porcine embryonic stem cells (ESCs) are excellent models for exploring embryogenesis, producing genetically enhanced farm animals, and improving breeding. Various chemicals have been applied to generate porcine ESCs from embryos, which differ from mouse and human ESC derivation. Wnt inhibitors XAV939 or IWR1 are required to isolate and maintain porcine ESCs. How Wnt inhibitors specify porcine ESC fate decisions remains poorly understood. Additionally, whether porcine ESCs can be converted to extraembryonic endoderm (XEN) cells without genetic interventions has not been reported. Here, it is reported that Wnt inhibitors (i.e., XAV939 and IWR1) safeguard porcine ESCs from acquiring the XEN lineage. Porcine ESCs rely on Wnt inhibitors to maintain pluripotency. Without them, porcine ESCs exit from pluripotency and convert to XEN cells. An efficient strategy and culture conditions are further developed to directly derive porcine XEN cells from ESCs without gene editing. The resulting XEN cells from ESCs exhibit similar transcriptome and chromatin accessibility features to XEN cells from embryos and contribute to mouse extraembryonic tissues. This study will deepen the understanding of porcine pluripotency, lay the foundation for deriving high-quality porcine ESCs with germline chimerism and transmission, and provide valuable materials to study extraembryonic development and lineage segregation in livestock.

Pluripotent cell states and fates in human embryo models

Pluripotency, the capacity to generate all cells of the body, is a defining property of a transient population of epiblast cells found in pre-, peri- and post-implantation mammalian embryos. As development progresses, the epiblast cells undergo dynamic transitions in pluripotency states, concurrent with the specification of extra-embryonic and embryonic lineages. Recently, stem cell-based models of pre- and post-implantation human embryonic development have been developed using stem cells that capture key properties of the epiblast at different developmental stages. Here, we review early primate development, comparing pluripotency states of the epiblast in vivo with cultured pluripotent cells representative of these states. We consider how the pluripotency status of the starting cells influences the development of human embryo models and, in turn, what we can learn about the human pluripotent epiblast. Finally, we discuss the limitations of these models and questions arising from the pioneering studies in this emerging field.

Primed bovine embryonic stem cell lines can be derived at diverse stages of blastocyst development with similar efficiency and molecular characteristics

In this study, we established bovine embryonic stem cell (bESC) lines from early (eBL) and full (BL) blastocysts to determine the efficiency of bESC derivation from an earlier embryonic stage and compare the characteristics of the resulting lines. Using established medium and protocols for derivation of primed bESCs from expanded blastocysts, we derived bESC lines from eBLs and BLs with the same efficiency (4/12 each, 33%). Regardless of original blastocyst stage, bESC lines had a similar phenotype, including differentiation capacity, stable karyotype, and pluripotency marker expression over feeder-free transition and long-term culture. Transcriptome and functional analyses indicated that eBL- and BL-derived lines were in primed pluripotency. We additionally compared RNA-sequencing data from our lines to bovine embryos and stem cells from other recent reports, finding that base medium was the predominant source of variation among cell lines. In conclusion, our results show that indistinguishable bESC lines can be readily derived from eBL and BL, widening the pool of embryos available for bESC establishment. Finally, our investigation points to sources of variation in cell phenotype among recently reported bESC conditions, opening the door to future studies investigating the impact of factors aside from signaling molecules on ESC derivation, maintenance, and performance.

Capture primed pluripotency in guinea pig

Guinea pigs are valuable models for human disease research, yet the lack of established pluripotent stem cell lines has limited their utility. In this study, we isolate and characterize guinea pig epiblast stem cells (gpEpiSCs) from post-implantation embryos. These cells differentiate into the three germ layers, maintain normal karyotypes, and rely on FGF2 and ACTIVIN A signaling for self-renewal and pluripotency. Wingless/Integrated (WNT) signaling inhibition is also essential for their maintenance. GpEpiSCs express key pluripotency markers (OCT4, SOX2, NANOG) and share transcriptional similarities with human and mouse primed stem cells. While many genes are conserved between guinea pig and human primed stem cells, transcriptional analysis also reveals species-specific differences in pluripotency-related pathways. Epigenetic analysis highlights bivalent gene regulation, underscoring their developmental potential. This work demonstrates both the evolutionary conservation and divergence of primed pluripotent stem cells, providing a new tool for biomedical research and enhancing guinea pigs' utility in studying human diseases.

Tankyrase inhibitor IWR-1 modulates HIPPO and Transforming Growth Factor β signaling in primed bovine embryonic stem cells cultured on mouse embryonic fibroblasts

The use of tankyrase inhibitors is essential for capturing livestock embryonic stem cells (ESC), yet their mechanisms of action remain largely uncharacterized. Previous studies indicate that their roles extend beyond the suppression of canonical WNT signaling. This study investigates the effects of the tankyrase inhibitor IWR-1 on maintaining the pluripotency of bovine embryonic stem cells (bESC) cultured on mitotically inactivated mouse embryonic fibroblasts (MEF). Notably, bESC exhibited significant differentiation after one month of IWR-1 withdrawal, without a clear bias toward any specific germ layer. IWR-1 effectively inhibited TNKS2 activity in bESC, whereas it suppressed TNKS1 protein level in growth-arrested MEF. Early differentiation upon IWR-1 removal induced more substantial transcriptomic changes in MEF than in bESC. Furthermore, cell communication analysis predicted that IWR-1 influenced several paracrine and autocrine signals within the culture system. We also observed that IWR-1 repressed protein abundance of the HIPPO pathway components including TEAD4 and YAP1 in bESC and decreased transcription of HIPPO targeted genes CYR61. Protein analysis in growth-arrested MEF suggested that IWR-1 modulated MEF function by impeding TGF-β1 activation and activin A secretion which mitigated nuclear localization of SMAD2/3 in the bESC. This study underscores the role of tankyrase inhibitors in ESC self-renewal by modulating key signaling pathways and orchestrating cell-cell interactions, which may be meaningful in understanding the delicate signaling control of pluripotency in livestock and improving the culture system.

Review: Livestock cell types with myogenic differentiation potential: Considerations for the development of cultured meat

With the current environmental impact of large-scale animal production and societal concerns about the welfare of farm animals, researchers are questioning whether we can cultivate animal cells for the purpose of food production. This review focuses on a pivotal aspect of the cellular agriculture domain: cells. We summarised information on the various cell types from farm animals currently used for the development of cultured meat, including mesenchymal stromal cells, myoblasts, and pluripotent stem cells. The review delves into the advantages and limitations of each cell type and considers factors like the selection of the appropriate cell source, as well as cell culture conditions that influence cell performance. As current research in cultured meat seeks to create muscle fibers to mimic the texture and nutritional profile of meat, we focused on the myogenic differentiation capacity of the cells. The most commonly used cell type for this purpose are myoblasts or satellite cells, but given their limited proliferation capacity, efforts are underway to formulate myogenic differentiation protocols for mesenchymal stromal cells and pluripotent stem cells. The multipotent character of the latter cell types might enable the creation of other tissues found in meat, such as adipose and connective tissues. This review can help guiding the selection of a cell type or culture conditions in the context of cultured meat development.

A brief chronicle of research on human pluripotent stem cells

Today, human pluripotent stem cell technologies find widespread application across biomedical research, as models for early human development, as platforms for functional human genomics, as tools for the study of disease, drug screening and toxicology, and as a renewable source of cellular therapeutics for a range of intractable diseases. The foundations of this human pluripotent stem cell revolution rest on advances in a wide range of disciplines, including cancer biology, assisted reproduction, cell culture and organoid technology, somatic cell nuclear transfer, primate embryology, single-cell biology, and gene editing. This review surveys the slow emergence of the study of human pluripotency and the exponential growth of the field during the past several decades.

Propagating pluripotency - The conundrum of self-renewal

The discovery of mouse embryonic stem cells in 1981 transformed research in mammalian developmental biology and functional genomics. The subsequent generation of human pluripotent stem cells (PSCs) and the development of molecular reprogramming have opened unheralded avenues for drug discovery and cell replacement therapy. Here, I review the history of PSCs from the perspective that long-term self-renewal is a product of the in vitro signaling environment, rather than an intrinsic feature of embryos. I discuss the relationship between pluripotent states captured in vitro to stages of epiblast in the embryo and suggest key considerations for evaluation of PSCs. A remaining fundamental challenge is to determine whether naïve pluripotency can be propagated from the broad range of mammals by exploiting common principles in gene regulatory architecture.

Elucidation of the pluripotent potential of bovine embryonic lineages facilitates the establishment of formative stem cell lines

The establishment of epiblast-derived pluripotent stem cells (PSCs) from cattle, which are important domestic animals that provide humans with milk and meat while also serving as bioreactors for producing valuable proteins, poses a challenge due to the unclear molecular signaling required for embryonic epiblast development and maintenance of PSC self-renewal. Here, we selected six key stages of bovine embryo development (E5, E6, E7, E10, E12, and E14) to track changes in pluripotency and the dependence on signaling pathways via modified single-cell transcription sequencing technology. The remarkable similarity of the gene expression patterns between cattle and pigs during embryonic lineage development contributed to the successful establishment of bovine epiblast stem cells (bEpiSCs) using 3i/LAF (WNTi, GSK3βi, SRCi, LIF, Activin A, and FGF2) culture system. The generated bEpiSCs exhibited consistent expression patterns of formative epiblast pluripotency genes and maintained clonal morphology, normal karyotypes, and proliferative capacity for more than 112 passages. Moreover, these cells exhibited high-efficiency teratoma formation as well as the ability to differentiate into various cell lineages. The potential of bEpiSCs for myogenic differentiation, primordial germ cell like cells (PGCLCs) induction, and as donor cells for cell nuclear transfer was also assessed, indicating their promise in advancing cell-cultured meat production, gene editing, and animal breeding.

Enhancing the palatability of cultivated meat

Cultivated meat (CM) has transitioned from a futuristic concept to a present reality, with select products approved for consumption and sale in Singapore, Israel, and the USA. This evolution has emphasized scalable, cost-effective, and sustainable production, as well as navigation of regulatory pathways. As CM develops, a crucial challenge lies in delivering products that are highly appealing to consumers. Central to this will be refining CM palatability, a term encompassing food's taste, aroma, texture, tenderness, juiciness, and color. We explore the scientific and engineering approaches to producing palatable CM, including cell-line selection, cell differentiation, and post-processing techniques. This includes a discussion of the structural and compositional properties of meat that are intrinsically coupled to palatability.

Inhibition of BMP-mediated SMAD pathway supports the pluripotency of pig embryonic stem cells in the absence of feeder cells

Here, we examined the effects of the BMP signaling pathway inhibitor LDN-193189 on the pluripotency of porcine embryonic stem cells (ESCs) in the absence of feeder cells using molecular and transcriptomic techniques. Additionally, the effects of some extracellular matrix components on porcine ESC pluripotency were evaluated to develop an optimized and sustainable feeder-free culture system for porcine ESCs. Feeder cells were found to play an important role in supporting the pluripotency of porcine ESCs by blocking trophoblast and mesodermal differentiation through the inhibition of the BMP pathway. Additionally, treatment with LDN-193189, an inhibitor of the BMP pathway, maintained the pluripotency and homogeneity of porcine ESCs for an extended period in the absence of feeder cells by stimulating the secretion of chemokines and suppressing differentiation, based on transcriptome analysis. Conclusively, these results suggest that LDN-193189 could be a suitable replacement for feeder cells in the maintenance of porcine ESC pluripotency during culture. Additionally, these findings contribute to the understanding of pluripotency gene networks and comparative embryogenesis.

Establishment of porcine embryonic stem cells in simplified serum free media and feeder free expansion

BACKGROUND

The establishment of stable porcine embryonic stem cells (pESCs) can contribute to basic and biomedical research, including comparative developmental biology, as well as assessing the safety of stem cell-based therapies. Despite these advantages, most pESCs obtained from in vitro blastocysts require complex media and feeder layers, making routine use, genetic modification, and differentiation into specific cell types difficult. We aimed to establish pESCs with a single cell-passage ability, high proliferative potency, and stable in long-term culture from in vitro-derived blastocysts using a simplified serum-free medium.

METHODS

We evaluated the establishment efficiency of pESCs from in vitro blastocysts using various basal media (DMEM/F10 (1:1), DMEM/F12, and a-MEM) and factors (FGF2, IWR-1, CHIR99021, and WH-4-023). The pluripotency and self-renewal capacity of the established pESCs were analyzed under feeder or feeder-free conditions. Ultimately, we developed a simplified culture medium (FIW) composed of FGF2, IWR-1, and WH-4-023 under serum-free conditions.

RESULTS

The pESC-FIW lines were capable of single-cell passaging with short cell doubling times and expressed the pluripotency markers POU5F1, SOX2, and NANOG, as well as cell surface markers SSEA1, SSEA4, and TRA-1-60. pESC-FIW showed a stable proliferation rate and normal karyotype, even after 50 passages. Transcriptome analysis revealed that pESC-FIW were similar to reported pESC maintained in complex media and showed gastrulating epiblast cell characteristics. pESC-FIW were maintained for multiple passages under feeder-free conditions on fibronectin-coated plates using mTeSR™, a commercial medium used for feeder-free culture, exhibiting characteristics similar to those observed under feeder conditions.

CONCLUSIONS

These results indicated that inhibition of WNT and SRC was sufficient to establish pESCs capable of single-cell passaging and feeder-free expansion under serum-free conditions. The easy maintenance of pESCs facilitates their application in gene editing technology for agriculture and biomedicine, as well as lineage commitment studies.

Livestock embryonic stem cells for reproductive biotechniques and genetic improvement

Embryonic stem cells (ESCs) have proven to be a great in vitro model that faithfully recapitulates the events that occur during in vivo embryogenesis, making them a unique tool to study the cellular and molecular mechanisms that define tissue specification during embryonic development. Livestock ESCs are particularly attractive and have broad prospects including drug selection and human disease modeling, improvement of reproductive biotechniques and agriculture-related applications such as production of genetically modified animals. While mice and human ESCs have been established many years ago, no significant advances were made in livestock species until recently. Nowadays, livestock ESCs are available from cattle, pigs, sheep, horses and rabbits with different states of pluripotency. In this review, we summarize the current advances on livestock ESCs establishment and maintenance along with their present and future applications.

Smart proteins as a new paradigm for meeting dietary protein sufficiency of India: a critical review on the safety and sustainability of different protein sources

India, a global leader in agriculture, faces sustainability challenges in feeding its population. Although primarily a vegetarian population, the consumption of animal derived proteins has tremendously increased in recent years. Excessive dependency on animal proteins is not environmentally sustainable, necessitating the identification of alternative smart proteins. Smart proteins are environmentally benign and mimic the properties of animal proteins (dairy, egg and meat) and are derived from plant proteins, microbial fermentation, insects and cell culture meat (CCM) processes. This review critically evaluates the technological, safety, and sustainability challenges involved in production of smart proteins and their consumer acceptance from Indian context. Under current circumstances, plant-based proteins are most favorable; however, limited land availability and impending climate change makes them unsustainable in the long run. CCM is unaffordable with high input costs limiting its commercialization in near future. Microbial-derived proteins could be the most sustainable option for future owing to higher productivity and ability to grow on low-cost substrates. A circular economy approach integrating agri-horti waste valorization and C1 substrate synthesis with microbial biomass production offer economic viability. Considering the use of novel additives and processing techniques, evaluation of safety, allergenicity, and bioavailability of smart protein products is necessary before large-scale adoption.

Pig blastocyst-like structure models from embryonic stem cells

Pluripotent stem cells have the potential to generate embryo models that can recapitulate developmental processes in vitro. Large animals such as pigs may also benefit from stem-cell-based embryo models for improving breeding. Here, we report the generation of blastoids from porcine embryonic stem cells (pESCs). We first develop a culture medium 4FIXY to derive pESCs. We develop a 3D two-step differentiation strategy to generate porcine blastoids from the pESCs. The resulting blastoids exhibit similar morphology, size, cell lineage composition, and single-cell transcriptome characteristics to blastocysts. These porcine blastoids survive and expand for more than two weeks in vitro under two different culture conditions. Large animal blastoids such as those derived from pESCs may enable in vitro modeling of early embryogenesis and improve livestock species' breeding practices.

The progress of induced pluripotent stem cells derived from pigs: a mini review of recent advances

Pigs (Sus scrofa) are widely acknowledged as an important large mammalian animal model due to their similarity to human physiology, genetics, and immunology. Leveraging the full potential of this model presents significant opportunities for major advancements in the fields of comparative biology, disease modeling, and regenerative medicine. Thus, the derivation of pluripotent stem cells from this species can offer new tools for disease modeling and serve as a stepping stone to test future autologous or allogeneic cell-based therapies. Over the past few decades, great progress has been made in establishing porcine pluripotent stem cells (pPSCs), including embryonic stem cells (pESCs) derived from pre- and peri-implantation embryos, and porcine induced pluripotent stem cells (piPSCs) using a variety of cellular reprogramming strategies. However, the stabilization of pPSCs was not as straightforward as directly applying the culture conditions developed and optimized for murine or primate PSCs. Therefore, it has historically been challenging to establish stable pPSC lines that could pass stringent pluripotency tests. Here, we review recent advances in the establishment of stable porcine PSCs. We focus on the evolving derivation methods that eventually led to the establishment of pESCs and transgene-free piPSCs, as well as current challenges and opportunities in this rapidly advancing field.

A single-cell atlas of pig gastrulation as a resource for comparative embryology

Cell-fate decisions during mammalian gastrulation are poorly understood outside of rodent embryos. The embryonic disc of pig embryos mirrors humans, making them a useful proxy for studying gastrulation. Here we present a single-cell transcriptomic atlas of pig gastrulation, revealing cell-fate emergence dynamics, as well as conserved and divergent gene programs governing early porcine, primate, and murine development. We highlight heterochronicity in extraembryonic cell-types, despite the broad conservation of cell-type-specific transcriptional programs. We apply these findings in combination with functional investigations, to outline conserved spatial, molecular, and temporal events during definitive endoderm specification. We find early FOXA2 + /TBXT- embryonic disc cells directly form definitive endoderm, contrasting later-emerging FOXA2/TBXT+ node/notochord progenitors. Unlike mesoderm, none of these progenitors undergo epithelial-to-mesenchymal transition. Endoderm/Node fate hinges on balanced WNT and hypoblast-derived NODAL, which is extinguished upon endodermal differentiation. These findings emphasise the interplay between temporal and topological signalling in fate determination during gastrulation.

An optimized culture system for efficient derivation of porcine expanded potential stem cells from preimplantation embryos and by reprogramming somatic cells

Pigs share anatomical and physiological traits with humans and can serve as a large-animal model for translational medicine. Bona fide porcine pluripotent stem cells (PSCs) could facilitate testing cell and drug therapies. Agriculture and biotechnology may benefit from the ability to produce immune cells for studying animal infectious diseases and to readily edit the porcine genome in stem cells. Isolating porcine PSCs from preimplantation embryos has been intensively attempted over the past decades. We previously reported the derivation of expanded potential stem cells (EPSCs) from preimplantation embryos and by reprogramming somatic cells of multiple mammalian species, including pigs. Porcine EPSCs (pEPSCs) self-renew indefinitely, differentiate into embryonic and extra-embryonic lineages, and permit precision genome editing. Here we present a highly reproducible experimental procedure and data of an optimized and robust porcine EPSC culture system and its use in deriving new pEPSC lines from preimplantation embryos and reprogrammed somatic cells. No particular expertise is required for the protocols, which take ~4-6 weeks to complete. Importantly, we successfully established pEPSC lines from both in vitro fertilized and somatic cell nuclear transfer-derived embryos. These new pEPSC lines proliferated robustly over long-term passaging and were amenable to both simple indels and precision genome editing, with up to 100% targeting efficiency. The pEPSCs differentiated into embryonic cell lineages in vitro and teratomas in vivo, and into porcine trophoblast stem cells in human trophoblast stem cell medium. We show here that pEPSCs have unique epigenetic features, particularly H3K27me3 levels substantially lower than fibroblasts.

Establishment of Transgene-Free Porcine Induced Pluripotent Stem Cells

Although protocols to generate authentic transgene-free mouse and human induced pluripotent stem cells (iPSCs) are now well established, standard methods for reprogramming porcine somatic cells still suffer from low efficiency and transgene retention. The Basic Protocol describes reprogramming procedures to establish transgene-free porcine iPSCs (PiPSCs) from porcine fibroblasts. This method uses episomal plasmids encoding POU5F1, SOX2, NANOG, KLF4, SV40LT, c-MYC, LIN28A, and microRNA-302/367, combined with an optimized medium, to establish PiPSC lines. Support protocols describe the establishment and characterization of clonal PiPSC lines, as well as the preparation of feeder cells and EBNA1 mRNA. This optimized, step-by-step approach tailored to this species enables the efficient derivation of PiPSCs in ∼4 weeks. The establishment of transgene-free PiPSCs provides a new and valuable model for studies of larger mammalian species' development, disease, and regenerative biology. © 2024 The Authors. Current Protocols published by Wiley Periodicals LLC. Basic Protocol: Reprogramming of porcine fibroblasts with episomal plasmids Support Protocol 1: Preparation of mouse embryonic fibroblasts for feeder layer Support Protocol 2: Preparation of in vitro-transcribed EBNA1 mRNA Support Protocol 3: Establishment of clonal porcine induced pluripotent stem cell (PiPSC) lines Support Protocol 4: PiPSC characterization: Genomic DNA PCR and RT-PCR Support Protocol 5: PiPSC characterization: Immunostaining.

Efficient derivation of embryonic stem cells and primordial germ cell-like cells in cattle

The induction of the germ cell lineage from pluripotent stem cells (in vitro gametogenesis) will help understand the mechanisms underlying germ cell differentiation and provide an alternative source of gametes for reproduction. This technology is especially important for cattle, which are among the most important livestock species for milk and meat production. Here, we developed a new method for robust induction of primordial germ cell-like cells (PGCLCs) from newly established bovine embryonic stem (bES) cells. First, we refined the pluripotent culture conditions for pre-implantation embryos and ES cells. Inhibition of RHO increased the number of epiblast cells in the pre-implantation embryos and dramatically improved the efficiency of ES cell establishment. We then determined suitable culture conditions for PGCLC differentiation using bES cells harboring BLIMP1-tdTomato and TFAP2C-mNeonGreen (BTTN) reporter constructs. After a 24-h culture with bone morphogenetic protein 4 (BMP4), followed by three-dimensional culture with BMP4 and a chemical agonist and WNT signaling chemical antagonist, bES cells became positive for the reporters. A set of primordial germ cells (PGC) marker genes, including PRDM1/BLIMP1, TFAP2C, SOX17, and NANOS3, were expressed in BTTN-positive cells. These bovine PGCLCs (bPGCLCs) were isolated as KIT/CD117-positive and CD44-negative cell populations. We anticipate that this method for the efficient establishment of bES cells and induction of PGCLCs will be useful for stem cell-based reproductive technologies in cattle.

Hallmarks of totipotent and pluripotent stem cell states

Though totipotency and pluripotency are transient during early embryogenesis, they establish the foundation for the development of all mammals. Studying these in vivo has been challenging due to limited access and ethical constraints, particularly in humans. Recent progress has led to diverse culture adaptations of epiblast cells in vitro in the form of totipotent and pluripotent stem cells, which not only deepen our understanding of embryonic development but also serve as invaluable resources for animal reproduction and regenerative medicine. This review delves into the hallmarks of totipotent and pluripotent stem cells, shedding light on their key molecular and functional features.

Highly cooperative chimeric super-SOX induces naive pluripotency across species

Our understanding of pluripotency remains limited: iPSC generation has only been established for a few model species, pluripotent stem cell lines exhibit inconsistent developmental potential, and germline transmission has only been demonstrated for mice and rats. By swapping structural elements between Sox2 and Sox17, we built a chimeric super-SOX factor, Sox2-17, that enhanced iPSC generation in five tested species: mouse, human, cynomolgus monkey, cow, and pig. A swap of alanine to valine at the interface between Sox2 and Oct4 delivered a gain of function by stabilizing Sox2/Oct4 dimerization on DNA, enabling generation of high-quality OSKM iPSCs capable of supporting the development of healthy all-iPSC mice. Sox2/Oct4 dimerization emerged as the core driver of naive pluripotency with its levels diminished upon priming. Transient overexpression of the SK cocktail (Sox+Klf4) restored the dimerization and boosted the developmental potential of pluripotent stem cells across species, providing a universal method for naive reset in mammals.

Interspecies control of development during mammalian gastrulation

Gastrulation represents a pivotal phase of development and aberrations during this period can have major consequences, from minor anatomical deviations to severe congenital defects. Animal models are used to study gastrulation, however, there is considerable morphological and molecular diversity of gastrula across mammalian species. Here, we provide an overview of the latest research on interspecies developmental control across mammals. This includes single-cell atlases of several mammalian gastrula which have enabled comparisons of the temporal and molecular dynamics of differentiation. These studies highlight conserved cell differentiation regulators and both absolute and relative differences in differentiation dynamics between species. Recent advances in in vitro culture techniques have facilitated the derivation, maintenance and differentiation of cell lines from a range of species and the creation of multi-species models of gastrulation. Gastruloids are three-dimensional aggregates capable of self-organising and recapitulating aspects of gastrulation. Such models enable species comparisons outside the confines of the embryo. We highlight recent in vitro evidence that differentiation processes such as somitogenesis and neuronal maturation scale with known in vivo differences in developmental tempo across species. This scaling is likely due to intrinsic differences in cell biochemistry. We also highlight several studies which provide examples of cell differentiation dynamics being influenced by extrinsic factors, including culture conditions, chimeric co-culture, and xenotransplantation. These collective studies underscore the complexity of gastrulation across species, highlighting the necessity of additional datasets and studies to decipher the intricate balance between intrinsic cellular programs and extrinsic signals in shaping embryogenesis.

Efficient derivation of transgene-free porcine induced pluripotent stem cells enables in vitro modeling of species-specific developmental timing

Sus scrofa domesticus (pig) has served as a superb large mammalian model for biomedical studies because of its comparable physiology and organ size to humans. The derivation of transgene-free porcine induced pluripotent stem cells (PiPSCs) will, therefore, benefit the development of porcine-specific models for regenerative biology and its medical applications. In the past, this effort has been hampered by a lack of understanding of the signaling milieu that stabilizes the porcine pluripotent state in vitro. Here, we report that transgene-free PiPSCs can be efficiently derived from porcine fibroblasts by episomal vectors along with microRNA-302/367 using optimized protocols tailored for this species. PiPSCs can be differentiated into derivatives representing the primary germ layers in vitro and can form teratomas in immunocompromised mice. Furthermore, the transgene-free PiPSCs preserve intrinsic species-specific developmental timing in culture, known as developmental allochrony. This is demonstrated by establishing a porcine in vitro segmentation clock model that, for the first time, displays a specific periodicity at ∼3.7 h, a timescale recapitulating in vivo porcine somitogenesis. We conclude that the transgene-free PiPSCs can serve as a powerful tool for modeling development and disease and developing transplantation strategies. We also anticipate that they will provide insights into conserved and unique features on the regulations of mammalian pluripotency and developmental timing mechanisms.

OCT4 regulates WNT/β-catenin signaling and prevents mesoendoderm differentiation by repressing EOMES in porcine pluripotent stem cells

The regulatory network between signaling pathways and transcription factors (TFs) is crucial for the maintenance of pluripotent stem cells. However, little is known about how the key TF OCT4 coordinates signaling pathways to regulate self-renewal and lineage differentiation of porcine pluripotent stem cells (pPSCs). Here, we explored the function of OCT4 in pPSCs by transcriptome and chromatin accessibility analysis. The TFs motif enrichment analysis revealed that, following OCT4 knockdown, the regions of increased chromatin accessibility were enriched with EOMES, GATA6, and FOXA1, indicating that pPSCs differentiated toward the mesoendoderm (ME) lineage. Besides, pPSCs rapidly differentiated into ME when the WNT/β-catenin inhibitor XAV939 was removed. However, the ME differentiation of pPSCs caused by OCT4 knockdown did not rely on the activation of WNT/β-catenin signaling because the target gene of WNT/β-catenin signaling, AXIN2 was not upregulated after OCT4 knockdown, despite significant upregulation of WLS and some WNT ligands. Importantly, OCT4 is directly bound to the promoter and enhancers of EOMES and repressed its transcription. Overexpression of EOMES was sufficient to induce ME differentiation in the presence of XAV939. These results demonstrate that OCT4 can regulate WNT/β-catenin signaling and prevent ME differentiation of pPSCs by repressing EOMES transcription.

From fertilised oocyte to cultivated meat - harnessing bovine embryonic stem cells in the cultivated meat industry

Global demand for animal protein is on the rise, but many practices common in conventional production are no longer scalable due to environmental impact, public health concerns, and fragility of food systems. For these reasons and more, a pressing need has arisen for sustainable, nutritious, and animal welfare-conscious sources of protein, spurring research dedicated to the production of cultivated meat. Meat mainly consists of muscle, fat, and connective tissue, all of which can be sourced and differentiated from pluripotent stem cells to resemble their nutritional values in muscle tissue. In this paper, we outline the approach that we took to derive bovine embryonic stem cell lines (bESCs) and to characterise them using FACS (fluorescence-activated cell sorting), real-time PCR and immunofluorescence staining. We show their cell growth profile and genetic stability and demonstrate their induced differentiation to mesoderm committed cells. In addition, we discuss our strategy for preparation of master and working cell banks, by which we can expand and grow cells in suspension in quantities suitable for mass production. Consequently, we demonstrate the potential benefits of harnessing bESCs in the production of cultivated meat.

Generation of stable integration-free pig induced pluripotent stem cells under chemically defined culture condition

Genome integration-free pig induced pluripotent stem cells (iPSCs) bring tremendous value in pre-clinical testing of regenerative medicine, as well as conservation and exploitation of endangered or rare local pig idioplasmatic resources. However, due to a lack of appropriate culture medium, efficient induction and stable maintenance of pig iPSCs with practical value remains challenging. Here, we established an efficient induction system for exogenous gene-independent iPSCs under chemically defined culture condition previously used for generation of stable pig pre-gastrulation epiblast stem cells (pgEpiSCs). WNT suppression was found to play an essential role in establishment of exogenous gene-independent iPSCs. Strikingly, stable integration-free pig iPSCs could be established from pig somatic cells using episomal vectors in this culture condition. The iPSCs had pluripotency features and transcriptome characteristics approximating pgEpiSCs. More importantly, this induction system may be used to generate integration-free iPSCs from elderly disabled rare local pig somatic cells and the iPSCs could be gene-edited and used as donor cells for nuclear transfer. Our results provide novel insights into potential applications for genetic breeding of livestock species and pre-clinical evaluation of regenerative medicine.

Stem cell-based strategies and challenges for production of cultivated meat

Cultivated meat scale-up and industrial production will require multiple stable cell lines from different species to recreate the organoleptic and nutritional properties of meat from livestock. In this Review, we explore the potential of stem cells to create the major cellular components of cultivated meat. By using developments in the fields of tissue engineering and biomedicine, we explore the advantages and disadvantages of strategies involving primary adult and pluripotent stem cells for generating cell sources that can be grown at scale. These myogenic, adipogenic or extracellular matrix-producing adult stem cells as well as embryonic or inducible pluripotent stem cells are discussed for their proliferative and differentiation capacity, necessary for cultivated meat. We examine the challenges for industrial scale-up, including differentiation and culture protocols, as well as genetic modification options for stem cell immortalization and controlled differentiation. Finally, we discuss stem cell-related safety and regulatory challenges for bringing cultivated meat to the marketplace.

Chimaeras, complementation, and controlling the male germline

Animal breeding drives genetic progress mainly through the male germline. This process is slow to respond to rapidly mounting environmental pressures that threaten sustainable food security from animal protein production. New approaches promise to accelerate breeding by producing chimaeras, which comprise sterile host and fertile donor genotypes, to exclusively transmit elite male germlines. Following gene editing to generate sterile host cells, the missing germline can be restored by transplanting either: (i) spermatogonial stem cells (SSCs) into the testis; or (ii) embryonic stem cells (ESCs) into early embryos. Here we compare these alternative germline complementation strategies and their impact on agribiotechnology and species conservation. We propose a novel breeding platform that integrates embryo-based complementation with genomic selection, multiplication, and gene modification.

Rat post-implantation epiblast-derived pluripotent stem cells produce functional germ cells

In mammals, pluripotent cells transit through a continuum of distinct molecular and functional states en route to initiating lineage specification. Capturing pluripotent stem cells (PSCs) mirroring in vivo pluripotent states provides accessible in vitro models to study the pluripotency program and mechanisms underlying lineage restriction. Here, we develop optimal culture conditions to derive and propagate post-implantation epiblast-derived PSCs (EpiSCs) in rats, a valuable model for biomedical research. We show that rat EpiSCs (rEpiSCs) can be reset toward the naive pluripotent state with exogenous Klf4, albeit not with the other five candidate genes (Nanog, Klf2, Esrrb, Tfcp2l1, and Tbx3) effective in mice. Finally, we demonstrate that rat EpiSCs retain competency to produce authentic primordial germ cell-like cells that undergo functional gametogenesis leading to the birth of viable offspring. Our findings in the rat model uncover principles underpinning pluripotency and germline competency across species.

Human and Pig Pluripotent Stem Cells: From Cellular Products to Organogenesis and Beyond

Pluripotent stem cells (PSCs) are important for studying development and hold great promise in regenerative medicine due to their ability to differentiate into various cell types. In this review, we comprehensively discuss the potential applications of both human and pig PSCs and provide an overview of the current progress and challenges in this field. In addition to exploring the therapeutic uses of PSC-derived cellular products, we also shed light on their significance in the study of interspecies chimeras, which has led to the creation of transplantable human or humanized pig organs. Moreover, we emphasize the importance of pig PSCs as an ideal cell source for genetic engineering, facilitating the development of genetically modified pigs for pig-to-human xenotransplantation. Despite the achievements that have been made, further investigations and refinement of PSC technologies are necessary to unlock their full potential in regenerative medicine and effectively address critical healthcare challenges.

Lab partners: oocytes, embryos and company. A personal view on aspects of oocyte maturation and the development of monozygotic twins

The present review addresses the oocyte and the preimplantation embryo, and is intended to highlight the underlying principle of the "nature versus/and nurture" question. Given the diversity in mammalian oocyte maturation, this review will not be comprehensive but instead will focus on the porcine oocyte. Historically, oogenesis was seen as the development of a passive cell nursed and determined by its somatic compartment. Currently, the advanced analysis of the cross-talk between the maternal environment and the oocyte shows a more balanced relationship: Granulosa cells nurse the oocyte, whereas the latter secretes diffusible factors that regulate proliferation and differentiation of the granulosa cells. Signal molecules of the granulosa cells either prevent the precocious initiation of meiotic maturation or enable oocyte maturation following hormonal stimulation. A similar question emerges in research on monozygotic twins or multiples: In Greek and medieval times, twins were not seen as the result of the common course of nature but were classified as faults. This seems still valid today for the rare and until now mainly unknown genesis of facultative monozygotic twins in mammals. Monozygotic twins are unique subjects for studies of the conceptus-maternal dialogue, the intra-pair similarity and dissimilarity, and the elucidation of the interplay between nature and nurture. In the course of in vivo collections of preimplantation sheep embryos and experiments on embryo splitting and other microsurgical interventions we recorded observations on double blastocysts within a single zona pellucida, double inner cell masses in zona-enclosed blastocysts and double germinal discs in elongating embryos. On the basis of these observations we add some pieces to the puzzle of the post-zygotic genesis of monozygotic twins and on maternal influences on the developing conceptus.

Repurposing biomedical muscle tissue engineering for cellular agriculture: challenges and opportunities

Cellular agriculture is an emerging field rooted in engineering meat-mimicking cell-laden structures using tissue engineering practices that have been developed for biomedical applications, including regenerative medicine. Research and industrial efforts are focused on reducing the cost and improving the throughput of cultivated meat (CM) production using these conventional practices. Due to key differences in the goals of muscle tissue engineering for biomedical versus food applications, conventional strategies may not be economically and technologically viable or socially acceptable. In this review, these two fields are critically compared, and the limitations of biomedical tissue engineering practices in achieving the important requirements of food production are discussed. Additionally, the possible solutions and the most promising biomanufacturing strategies for cellular agriculture are highlighted.

Bovine blastocyst-like structures derived from stem cell cultures

Understanding the mechanisms of blastocyst formation and implantation is critical for improving farm animal reproduction but is hampered by a limited supply of embryos. Here, we developed an efficient method to generate bovine blastocyst-like structures (termed blastoids) via assembling bovine trophoblast stem cells and expanded potential stem cells. Bovine blastoids resemble blastocysts in morphology, cell composition, single-cell transcriptomes, in vitro growth, and the ability to elicit maternal recognition of pregnancy following transfer to recipient cows. Bovine blastoids represent an accessible in vitro model for studying embryogenesis and improving reproductive efficiency in livestock species.

Review: Progress in producing chimeric ungulate livestock for agricultural applications

The progress made in recent years in the derivation and culture of pluripotent stem cells from farm animals opens up the possibility of creating livestock chimeras. Chimeras producing gametes exclusively derived from elite donor stem cells could pass superior genetics on to the next generation and thereby reduce the genetic lag that typically exists between the elite breeding sector and the commercial production sector, especially for industries like beef and sheep where genetics is commonly disseminated through natural service mating. Chimeras carrying germ cells generated from genome-edited or genetically engineered pluripotent stem cells could further disseminate useful genomic alterations such as climate adaptation, animal welfare improvements, the repair of deleterious genetic conditions, and/or the elimination of undesired traits such as disease susceptibility to the next generation. Despite the successful production of chimeras with germ cells generated from pluripotent donor stem cells injected into preimplantation-stage blastocysts in model species, there are no documented cases of this occurring in livestock. Here, we review the literature on the derivation of pluripotent stem cells from ungulates, and progress in the production of chimeric ungulate livestock for agricultural applications, drawing on insights from studies done in model species, and discuss future possibilities of this fast-moving and developing field. Aside from the technical aspects, the consistency of the regulatory approach taken by different jurisdictions towards chimeric ungulate livestock with germ cells generated from pluripotent stem cells and their progeny will be an important determinant of breeding industry uptake and adoption in animal agriculture.

Review: Embryonic stem cells as tools for in vitro gamete production in livestock

The goal of in vitro gametogenesis is to reproduce the events of sperm and oocyte development in the laboratory. Significant advances have been made in the mouse in the last decade, but evolutionary divergence from the murine developmental program has prevented the replication of these advances in large mammals. In recent years, intensive work has been done in humans, non-human primates and livestock to elucidate species-specific differences that regulate germ cell development, due to the number of potential applications. One of the most promising applications is the use of in vitro gametes to optimize the spread of elite genetics in cattle. In this context, embryonic stem cells have been posed as excellent candidates for germ cell platforms. Here, we present the most relevant advances in in vitro gametogenesis of interest to livestock science, including new types of pluripotent stem cells with potential for germline derivation, characterization of the signaling environment in the gonadal niche, and experimental systems used to reproduce different stages of germ cell development in the laboratory.

Review: A barnyard in the lab: prospect of generating animal germ cells for breeding and conservation

In vitro gametogenesis (IVG) offers broad opportunities for gaining detailed new mechanistic knowledge of germ cell biology that will enable progress in the understanding of human infertility, as well as for applications in the conservation of endangered species and for accelerating genetic selection of livestock. The realisation of this potential depends on overcoming key technical challenges and of gaining more detailed knowledge of the ontogeny and developmental programme in different species. Important differences in the molecular mechanisms of germ cell determination and epigenetic reprogramming between mice and other animals have been elucidated in recent years. These must be carefully considered when developing IVG protocols, as cellular kinetics in mice may not accurately reflect mechanisms in other mammals. Similarly, diverse stem cell models with potential for germ cell differentiation may reflect alternative routes to successful IVG. In conclusion, the fidelity of the developmental programme recapitulated during IVG must be assessed against reference information from each species to ensure the production of healthy animals using these methods, as well as for developing genuine models of gametogenesis.

Super-enhancers conserved within placental mammals maintain stem cell pluripotency

Despite pluripotent stem cells sharing key transcription factors, their maintenance involves distinct genetic inputs. Emerging evidence suggests that super-enhancers (SEs) can function as master regulatory hubs to control cell identity and pluripotency in humans and mice. However, whether pluripotency-associated SEs share an evolutionary origin in mammals remains elusive. Here, we performed comprehensive comparative epigenomic and transcription factor binding analyses among pigs, humans, and mice to identify pluripotency-associated SEs. Like typical enhancers, SEs displayed rapid evolution in mammals. We showed that BRD4 is an essential and conserved activator for mammalian pluripotency-associated SEs. Comparative motif enrichment analysis revealed 30 shared transcription factor binding motifs among the three species. The majority of transcriptional factors that bind to identified motifs are known regulators associated with pluripotency. Further, we discovered three pluripotency-associated SEs (SE-SOX2, SE-PIM1, and SE-FGFR1) that displayed remarkable conservation in placental mammals and were sufficient to drive reporter gene expression in a pluripotency-dependent manner. Disruption of these conserved SEs through the CRISPR-Cas9 approach severely impaired stem cell pluripotency. Our study provides insights into the understanding of conserved regulatory mechanisms underlying the maintenance of pluripotency as well as species-specific modulation of the pluripotency-associated regulatory networks in mammals.

Acquisition and maintenance of pluripotency are influenced by fibroblast growth factor, leukemia inhibitory factor, and 2i in bovine-induced pluripotent stem cells

Several opportunities for embryo development, stem cell maintenance, cell fate, and differentiation have emerged using induced pluripotent stem cells (iPSCs). However, the difficulty in comparing bovine iPSCs (biPSCs) with embryonic stem cells (ESCs) was a challenge for many years. Here, we reprogrammed fetal fibroblasts by transient expression of the four transcription factors (Oct4, Sox2, Klf4, and c-Myc, collectively termed “OSKM” factors) and cultured in iPSC medium, supplemented with bFGF, bFGF2i, leukemia inhibitory factor (LIF), or LIF2i, and then compared these biPSC lines with bESC to evaluate the pluripotent state. biPSC lines were generated in all experimental groups. Particularly, reprogrammed cells treated with bFGF were more efficient in promoting the acquisition of pluripotency. However, LIF2i treatment did not promote continuous self-renewal. biPSCs (line 2) labeled with GFP were injected into early embryos (day 4.5) to assess the potential to contribute to chimeric blastocysts. The biPSC lines show a pluripotency state and are differentiated into three embryonic layers. Moreover, biPSCs and bESCs labeled with GFP were able to contribute to chimeric blastocysts. Additionally, biPSCs have shown promising potential for contributing to chimeric blastocysts and for future studies.

Stepwise pluripotency transitions in mouse stem cells

Pluripotent cells in mouse embryos, which first emerge in the inner cell mass of the blastocyst, undergo gradual transition marked by changes in gene expression, developmental potential, polarity, and morphology as they develop from the pre-implantation until post-implantation gastrula stage. Recent studies of cultured mouse pluripotent stem cells (PSCs) have clarified the presence of intermediate pluripotent stages between the naïve pluripotent state represented by embryonic stem cells (ESCs-equivalent to the pre-implantation epiblast) and the primed pluripotent state represented by epiblast stem cells (EpiSCs-equivalent to the late post-implantation gastrula epiblast). In this review, we discuss these recent findings in light of our knowledge on peri-implantation mouse development and consider the implications of these new PSCs to understand their temporal sequence and the feasibility of using them as model system for pluripotency.

Research progress and application prospects of stable porcine pluripotent stem cells

Pluripotent stem cells (PSCs) harbor the capacity of unlimited self-renewal and multi-lineage differentiation potential which are crucial for basic research and biomedical science. Establishment of PSCs with defined features were previously reported from mice and humans, while generation of stable large animal PSCs has experienced a relatively long trial stage and only recently has made breakthroughs. Pigs are regarded as ideal animal models for their similarities in physiology and anatomy to humans. Generation of porcine PSCs would provide cell resources for basic research, genetic engineering, animal breeding and cultured meat. In this review, we summarize the progress on the derivation of porcine PSCs and reprogrammed cells and elucidate the mechanisms of pluripotency changes during pig embryo development. This will be beneficial for understanding the divergence and conservation between different species involved in embryo development and the pluripotent regulated signaling pathways. Finally, we also discuss the promising future applications of stable porcine PSCs.

Pluripotent Core in Bovine Embryos: A Review

Early development in mammals is characterized by the ability of each cell to produce a complete organism plus the extraembryonic, or placental, cells, defined as pluripotency. During subsequent development, pluripotency is lost, and cells begin to differentiate to a particular cell fate. This review summarizes the current knowledge of pluripotency features of bovine embryos cultured in vitro, focusing on the core of pluripotency genes (OCT4, NANOG, SOX2, and CDX2), and main chemical strategies for controlling pluripotent networks during early development. Finally, we discuss the applicability of manipulating pluripotency during the morula to blastocyst transition in cattle species.

In vitro investigation of mammalian peri-implantation embryogenesis†

The embryos attach and invade into the uterus and establish the connection with their mother in peri-implantation development. During this period, the pluripotent epiblast cells of embryo undergo symmetry breaking, cell lineage allocation, and morphogenetic remodeling, accompanying with the dramatic changes of transcriptome, epigenome, and signal pathways, to prepare a state for their differentiation and gastrulation. The progresses in mouse genetics and stem cell biology have largely advanced the knowledge of these transformations which are largely hindered by the hard accessibility of natural embryos. To gain insight into mammalian peri-implantation development, great efforts have been made in the field. Recently, the advances in the prolonged in vitro culture of blastocysts, the derivation of multiple pluripotent stem cells, as well as the construction of stem cell-based embryo-like models have opened novel avenues to investigate peri-implantation development in mammals, especially for the humans. Combining with other emerging new technologies, these new models will substantially promote the comprehension of mammalian peri-implantation development, accelerating the progress of reproductive and regenerative medicine.

The people behind the papers - Masaki Kinoshita, Toshihiro Kobayashi, Hiroshi Nagashima, Ramiro Alberio and Austin Smith

The ability to derive and maintain pluripotent stem cells (PSCs) from livestock species in defined media conditions will contribute to many new research avenues, including comparative embryology and xenotransplantation. In a new paper in Development, Masaki Kinoshita, Toshihiro Kobayashi, Hiroshi Nagashima, Ramiro Alberio, Austin Smith and colleagues describe their three-component medium, which supports long-term propagation of PSCs in the absence of feeders or serum factors. We caught up with the authors to find out more about their research and their future plans.