Totipotent embryonic stem cells arise in ground-state culture conditions

Totipotency or plenipotency: rethinking stem cell bipotentiality

The term 'totipotency' has often been misapplied in stem cell research to describe cells with embryonic and extraembryonic bipotentiality, despite a lack of evidence that they can generate an entire organism from a single cell. Additionally, no specific term currently distinguishes bipotential stem cells from pluripotent cells, which contribute poorly to extraembryonic tissues. This review examines the developmental continuum from totipotency to pluripotency in early embryos and revisits the previously proposed concept of plenipotency in preimplantation development. We evaluate emerging stem cell models that exhibit bipotentiality but have lost the ability to autonomously initiate and sustain the sequential fate decisions necessary to develop into a complete organism. Unlike totipotent embryonic cells, which retain the information required to initiate fate decisions at the correct timing and cell numbers, these stem cells have lost that capacity. This loss of critical developmental information distinguishes totipotency from plenipotency, with bipotential stem cells aligning more closely with the latter. By distinguishing plenipotency from totipotency and pluripotency, we aim to refine terminology, enhance our understanding of early embryonic development, and address ethical considerations in human research.

Differential Elasticity Affects Lineage Segregation of Embryonic Stem Cells

The question of what guides lineage segregation is central to development, where cellular differentiation leads to segregated cell populations destined for specialized functions. Here, using optical tweezers measurements of mouse embryonic stem cells, we reveal a mechanical mechanism based on differential elasticity in the second lineage segregation of the embryonic inner cell mass into epiblast (EPI) cells, which will develop into the fetus, and primitive endoderm (PrE), which will form extraembryonic structures such as the yolk sac. Remarkably, we find that these mechanical differences already occur during priming, not just after a cell has committed to differentiation. Specifically, we show that PrE-primed cells exhibit significantly higher elasticity than EPI-primed cells, characterized by lower power spectrum scaling exponents, higher Young's modulus, and lower loss tangent. Using a model of two cell types differing only in elasticity, we show that differential elasticity alone is sufficient to lead to segregation between cell types, suggesting that the mechanical attributes of the cells contribute to the segregation process. Importantly, we find that this process relies on cellular activity. Our findings present differential elasticity as a previously unknown mechanical contributor to lineage segregation during embryo morphogenesis.

Altering metabolism programs cell identity via NAD+-dependent deacetylation

Cells change their metabolic profiles in response to underlying gene regulatory networks, but how can alterations in metabolism encode specific transcriptional instructions? Here, we show that forcing a metabolic change in embryonic stem cells (ESCs) promotes a developmental identity that better approximates the inner cell mass (ICM) of the early mammalian blastocyst in cultures. This shift in cellular identity depends on the inhibition of glycolysis and stimulation of oxidative phosphorylation (OXPHOS) triggered by the replacement of D-glucose by D-galactose in ESC media. Enhanced OXPHOS in turn activates NAD + -dependent deacetylases of the Sirtuin family, resulting in the deacetylation of histones and key transcription factors to focus enhancer activity while reducing transcriptional noise, which results in a robustly enhanced ESC phenotype. This exploitation of a NAD + /NADH coenzyme coupled to OXPHOS as a means of programming lineage-specific transcription suggests new paradigms for how cells respond to alterations in their environment, and implies cellular rejuvenation exploits enzymatic activities for simultaneous activation of a discrete enhancer set alongside silencing genome-wide transcriptional noise.

Totipotent-like reprogramming: Molecular machineries and chemical manipulations

Embryonic stem cells (ESCs) exhibit remarkable pluripotency, possessing the dual abilities of self-renewal and differentiation into any cell type within the embryonic lineage. Among cultivated mouse ESCs, a subpopulation known as 2-cell-like cells (2CLCs) displays a transcriptomic signature reminiscent of the 2-cell embryonic stage, with the capacity to differentiate into both embryonic and extraembryonic tissues. These 2CLCs have served as an invaluable totipotent-like cell model for deciphering the cellular and molecular mechanisms underlying the establishment of totipotency. Accumulating evidence has indicated that a multitude of regulators including transcription factors, epigenetic modifications, and RNA regulators, exert crucial functions in the reprogramming of ESCs towards 2CLCs. In addition to 2CLCs, alternative totipotent-like cell types can be induced and maintained through the administration of single or combined chemical supplements, offering promising cell resources for regenerative medicine. In this review, we summarize the current advancements in the molecular regulations of 2CLCs and chemical manipulations of totipotent-like cells in mice, providing a foundation for understanding the regulatory networks underlying cell totipotency.

Divergent destinies: insights into the molecular mechanisms underlying EPI and PE fate determination

Mammalian pre-implantation development is entirely devoted to the specification of extra-embryonic lineages, which are fundamental for embryo morphogenesis and support. The second fate decision is taken just before implantation, as defined by the epiblast (EPI) and the primitive endoderm (PE) specification. Later, EPI forms the embryo proper and PE contributes to the formation of the yolk sac. The formation of EPI and PE as molecularly and morphologically distinct lineages is the final step of a multistage process, which begins when bipotent progenitor cells diverge into separate fates. Despite advances in uncovering the molecular mechanisms underlying the differential transcriptional patterns that dictate how apparently identical cells make fate decisions and how lineage integrity is maintained, a detailed overview of these mechanisms is still lacking. In this review, we dissect the EPI and PE formation process into four stages (initiation, specification, segregation, and maintenance) and we provide a comprehensive understanding of the molecular mechanisms involved in lineage establishment in the mouse. In addition, we discuss the conservation of key processes in humans, based on the most recent findings.

Downregulation of Pecam-1 is insufficient to redefine embryonic stem cells' fate toward PrE in chimaeric mouse blastocysts

In this work, we aimed to investigate whether Pecam-1 (platelet endothelial cell adhesion molecule 1) surface protein of ICM cells is involved in primitive endoderm (PrE) differentiation. For this purpose, we used embryonic stem cells (ESCs) as an in vitro model for ICM cells, and induced differentiation of ESCs into PrE cells by retinoic acid (RA). Using immunostaining, we observed that at the protein level Pecam-1 diminishes in the early stages of ESC differentiation towards PrE. It is known that in early blastocysts Pecam-1 is detected in all ICM cells, but after the segregation of the epiblast (EPI) and PrE layers, its presence is restricted to EPI cells. Moreover, it was previously reported that a population of ESCs with reduced SSEA-1 and Pecam-1 levels differentiates into PrE. Thus, we examined whether the absence of Pecam-1 in ESCs is sufficient to induce differentiation of these cells into the PrE. To this end, ESCs in which Pecam-1 expression had been downregulated by siRNA were microinjected into 8-cell and blastocyst stage embryos. We found that not only the modified ESCs failed to differentiate into PrE, but similarly to the unmodified control cells, integrated within the EPI. This indicates that the decrease in Pecam-1 expression is not sufficient to promote the differentiation of ESCs into PrE in chimaeric embryos.

Extra-embryonic mesoderm during development and in in vitro models

Extra-embryonic tissues provide protection and nutrition in vertebrates, as well as a connection to the maternal tissues in mammals. The extra-embryonic mesoderm is an essential and understudied germ layer present in amniotes. It is involved in hematopoiesis, as well as in the formation of extra-embryonic structures such as the amnion, umbilical cord and placenta. The origin and specification of extra-embryonic mesoderm are not entirely conserved across species, and the molecular mechanisms governing its formation and function are not fully understood. This Review begins with an overview of the embryonic origin and function of extra-embryonic mesoderm in vertebrates from in vivo studies. We then compare in vitro models that generate extra-embryonic mesoderm-like cells. Finally, we discuss how insights from studying both embryos and in vitro systems can aid in designing even more advanced stem cell-based embryo models.

Deep learning-based models for preimplantation mouse and human embryos based on single-cell RNA sequencing

The rapid growth of single-cell transcriptomic technology has produced an increasing number of datasets for both embryonic development and in vitro pluripotent stem cell-derived models. This avalanche of data surrounding pluripotency and the process of lineage specification has meant it has become increasingly difficult to define specific cell types or states in vivo, and compare these with in vitro differentiation. Here we utilize a set of deep learning tools to integrate and classify multiple datasets. This allows the definition of both mouse and human embryo cell types, lineages and states, thereby maximizing the information one can garner from these precious experimental resources. Our approaches are built on recent initiatives for large-scale human organ atlases, but here we focus on material that is difficult to obtain and process, spanning early mouse and human development. Using publicly available data for these stages, we test different deep learning approaches and develop a model to classify cell types in an unbiased fashion at the same time as defining the set of genes used by the model to identify lineages, cell types and states. We used our models trained on in vivo development to classify pluripotent stem cell models for both mouse and human development, showcasing the importance of this resource as a dynamic reference for early embryogenesis.

PRC2 promotes canalisation during endodermal differentiation

The genetic circuitry that encodes the developmental programme of mammals is regulated by transcription factors and chromatin modifiers. During early gestation, the three embryonic germ layers are established in a process termed gastrulation. The impact of deleterious mutations in chromatin modifiers such as the polycomb proteins manifests during gastrulation, leading to early developmental failure and lethality in mouse models. Embryonic stem cells have provided key insights into the molecular function of polycomb proteins, but it is impossible to fully appreciate the role of these epigenetic factors in development, or how development is perturbed due to their deficiency, in the steady-state. To address this, we have employed a tractable embryonic stem cell differentiation system to model primitive streak formation and early gastrulation. Using this approach, we find that loss of the repressive polycomb mark H3K27me3 is delayed relative to transcriptional activation, indicating a subordinate rather than instructive role in gene repression. Despite this, chemical inhibition of polycomb enhanced endodermal differentiation efficiency, but did so at the cost of lineage fidelity. These findings highlight the importance of the polycomb system in stabilising the developmental transcriptional response and, in so doing, in shoring up cellular specification.

Relationship of PSC to embryos: Extending and refining capture of PSC lines from mammalian embryos

Pluripotent stem cell lines derived from preimplantation mouse embryos have opened opportunities for the study of early mammalian development and generation of genetically uncompromised material for differentiation into specific cell types. Murine embryonic stem cells are highly versatile and can be engineered and introduced into host embryos, transferred to recipient females, and gestated to investigate gene function at multiple levels as well as developmental mechanisms, including lineage segregation and cell competition. In this review, we summarize the biomedical motivation driving the incremental modification to culture regimes and analyses that have advanced stem cell research to its current state. Ongoing investigation into divergent mechanisms of early developmental processes adopted by other species, such as agriculturally beneficial mammals and birds, will continue to enrich knowledge and inform strategies for future in vitro models.

In vitro generation of trophoblast like stem cells from goat pluripotent stem cells

Since the first mouse induced pluripotent stem cells (iPSCs) was derived, the in vitro culture of domestic iPSCs functionally and molecularly comparable with mouse iPSCs has been a challenge. Here, we established dairy goat iPSCs (giPSCs) from goat ear fibroblast cells with mouse iPSCs morphology, the expression of pluripotent markers and differentiation ability in vitro delivered by piggyBac transposon with nine Dox-inducible exogenous reprogramming factors. These reprogramming factors were bOMSK (bovine OCT4, CMYC, SOX2, and KLF4), pNhL (porcine NANOG and human LIN28), hRL (human RARG and LRH1), and SV40 Large T. Notably, AF-giPSCs (induced in activin A and bFGF condition) were capable of differentiation in embryoid bodies in vitro and could contribute to interspecies chimerism in mouse E6.5 embryos in vitro, demonstrating that AF-giPSCs have the developmental capability to generate some embryonic cell lineages. Moreover, Wnt/β-catenin signaling has an important role in driving goat induced trophoblast-like stem cells (giTLSCs) from Dox-independent giPSCs. This study will support further establishment of the stable giPSC lines without any integration of exogenous genes.

The primitive endoderm supports lineage plasticity to enable regulative development

Mammalian blastocyst formation involves the specification of the trophectoderm followed by the differentiation of the inner cell mass into embryonic epiblast and extra-embryonic primitive endoderm (PrE). During this time, the embryo maintains a window of plasticity and can redirect its cellular fate when challenged experimentally. In this context, we found that the PrE alone was sufficient to regenerate a complete blastocyst and continue post-implantation development. We identify an in vitro population similar to the early PrE in vivo that exhibits the same embryonic and extra-embryonic potency and can form complete stem cell-based embryo models, termed blastoids. Commitment in the PrE is suppressed by JAK/STAT signaling, collaborating with OCT4 and the sustained expression of a subset of pluripotency-related transcription factors that safeguard an enhancer landscape permissive for multi-lineage differentiation. Our observations support the notion that transcription factor persistence underlies plasticity in regulative development and highlight the importance of the PrE in perturbed development.

Acquisition of 2C-like totipotency through defined maternal-effect factors

Fully grown oocytes have the natural ability to transform 2 terminally differentiated gametes into a totipotent zygote representing the acquisition of totipotency. This process wholly depends on maternal-effect factors (MFs). MFs stored in the eggs are therefore likely to be able to induce cellular reprogramming to a totipotency state. Here we report the generation of totipotent-like stem cells from mESCs using 4MFs Hsf1, Zar1, Padi6, and Npm2, designated as MFiTLSCs. MFiTLSCs exhibited a unique and inherent capability to differentiate into embryonic and extraembryonic derivatives. Transcriptomic analysis revealed that MFiTLSCs are enriched with 2-cell-specific genes that appear to synergistically induce a transcriptional repressive state, in that parental genomes are remodeled to a poised transcriptional repression state while totipotency is established following fertilization. This method to derive MFiTLSCs could help advance the understanding of fate determinations of totipotent stem cells in a physiological context and establish a foundation for the development of oocyte biology-based reprogramming technology.

Exposure of chimaeric embryos to exogenous FGF4 leads to the production of pure ESC-derived mice

Producing chimaeras constitutes the most reliable method of verifying the pluripotency of newly established cells. Moreover, forming chimaeras by injecting genetically modified embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) into the embryo is part of the procedure for generating transgenic mice, which are used for understanding gene function. Conventional methods for generating transgenic mice, including the breeding of chimaeras and tetraploid complementation, are time-consuming and cost-inefficient, with significant limitations that hinder their effectiveness and widespread applications. In the present study, we modified the traditional method of chimaera generation to significantly speed up this process by generating mice exclusively derived from ESCs. This study aimed to assess whether fully ESC-derived mice could be obtained by modulating fibroblast growth factor 4 (FGF4) levels in the culture medium and changing the direction of cell differentiation in the chimaeric embryo. We found that exogenous FGF4 directs all host blastomeres to the primitive endoderm fate, but does not affect the localisation of ESCs in the epiblast of the chimaeric embryos. Consequently, all FGF4-treated chimaeric embryos contained an epiblast composed exclusively of ESCs, and following transfer into recipient mice, these embryos developed into fully ESC-derived newborns. Collectively, this simple approach could accelerate the generation of ESC-derived animals and thus optimise ESC-mediated transgenesis and the verification of cell pluripotency. Compared to traditional methods, it could speed up functional studies by several weeks and significantly reduce costs related to maintaining and breeding chimaeras. Moreover, since the effect of stimulating the FGF signalling pathway is universal across different animal species, our approach can be applied not only to rodents but also to other animals, offering its utility beyond laboratory settings.

Transcription factor co-expression mediates lineage priming for embryonic and extra-embryonic differentiation

In early mammalian development, cleavage stage blastomeres and inner cell mass (ICM) cells co-express embryonic and extra-embryonic transcriptional determinants. Using a protein-based double reporter we identify an embryonic stem cell (ESC) population that co-expresses the extra-embryonic factor GATA6 alongside the embryonic factor SOX2. Based on single cell transcriptomics, we find this population resembles the unsegregated ICM, exhibiting enhanced differentiation potential for endoderm while maintaining epiblast competence. To relate transcription factor binding in these cells to future fate, we describe a complete enhancer set in both ESCs and naive extra-embryonic endoderm stem cells and assess SOX2 and GATA6 binding at these elements in the ICM-like ESC sub-population. Both factors support cooperative recognition in these lineages, with GATA6 bound alongside SOX2 on a fraction of pluripotency enhancers and SOX2 alongside GATA6 more extensively on endoderm enhancers, suggesting that cooperative binding between these antagonistic factors both supports self-renewal and prepares progenitor cells for later differentiation.

Efficient Reprogramming of Mouse Embryonic Stem Cells into Trophoblast Stem-like Cells via Lats Kinase Inhibition

Mouse zygotes undergo multiple rounds of cell division, resulting in the formation of preimplantation blastocysts comprising three lineages: trophectoderm (TE), epiblast (EPI), and primitive endoderm (PrE). Cell fate determination plays a crucial role in establishing a healthy pregnancy. The initial separation of lineages gives rise to TE and inner cell mass (ICM), from which trophoblast stem cells (TSC) and embryonic stem cells (ESC) can be derived in vitro. Studying lineage differentiation is greatly facilitated by the clear functional distinction between TSC and ESC. However, transitioning between these two types of cells naturally poses challenges. In this study, we demonstrate that inhibiting LATS kinase promotes the conversion of ICM to TE and also effectively reprograms ESC into stable, self-renewing TS-like cells (TSLC). Compared to TSC, TSLC exhibits similar molecular properties, including the high expression of marker genes such as Cdx2, Eomes, and Tfap2c, as well as hypomethylation of their promoters. Importantly, TSLC not only displays the ability to differentiate into mature trophoblast cells in vitro but also participates in placenta formation in vivo. These findings highlight the efficient reprogramming of ESCs into TSLCs using a small molecular inducer, which provides a new reference for understanding the regulatory network between ESCs and TSCs.

In vitro models of human hypoblast and mouse primitive endoderm

The primitive endoderm (PrE, also named hypoblast), a predominantly extraembryonic epithelium that arises from the inner cell mass (ICM) of the mammalian pre-implantation blastocyst, plays a fundamental role in embryonic development, giving rise to the yolk sac, establishing the anterior-posterior axis and contributing to the gut. PrE is specified from the ICM at the same time as the epiblast (Epi) that will form the embryo proper. While in vitro cell lines resembling the pluripotent Epi have been derived from a variety of conditions, only one model system currently exists for the PrE, naïve extraembryonic endoderm (nEnd). As a result, considerably more is known about the gene regulatory networks and signalling requirements of pluripotent stem cells than nEnd. In this review, we describe the ontogeny and differentiation of the PrE or hypoblast in mouse and primate and then discuss in vitro cell culture models for different extraembryonic endodermal cell types.

In vitro generation of mouse morula-like cells

Generating cells with the molecular and functional properties of embryo cells and with full developmental potential is an aim with fundamental biological significance. Here we report the in vitro generation of mouse transient morula-like cells (MLCs) via the manipulation of signaling pathways. MLCs are molecularly distinct from embryonic stem cells (ESCs) and cluster instead with embryo 8- to 16-cell stage cells. A single MLC can generate a blastoid, and the efficiency increases to 80% when 8-10 MLCs are used. MLCs make embryoids directly, efficiently, and within 4 days. Transcriptomic analysis shows that day 4-5 MLC-derived embryoids contain the cell types found in natural embryos at early gastrulation. Furthermore, MLCs introduced into morulae segregate into epiblast (EPI), primitive endoderm (PrE), and trophectoderm (TE) fates in blastocyst chimeras and have a molecular signature indistinguishable from that of host embryo cells. These findings represent the generation of cells that are molecularly and functionally similar to the precursors of the first three cell lineages of the embryo.

p16High senescence restricts cellular plasticity during somatic cell reprogramming

Despite advances in four-factor (4F)-induced reprogramming (4FR) in vitro and in vivo, how 4FR interconnects with senescence remains largely under investigated. Here, using genetic and chemical approaches to manipulate senescent cells, we show that removal of p16High cells resulted in the 4FR of somatic cells into totipotent-like stem cells. These cells expressed markers of both pluripotency and the two-cell embryonic state, readily formed implantation-competent blastoids and, following morula aggregation, contributed to embryonic and extraembryonic lineages. We identified senescence-dependent regulation of nicotinamide N-methyltransferase as a key mechanism controlling the S-adenosyl-L-methionine levels during 4FR that was required for expression of the two-cell genes and acquisition of an extraembryonic potential. Importantly, a partial 4F epigenetic reprogramming in old mice was able to reverse several markers of liver aging only in conjunction with the depletion of p16High cells. Our results show that the presence of p16High senescent cells limits cell plasticity, whereas their depletion can promote a totipotent-like state and histopathological tissue rejuvenation during 4F reprogramming.

Symmetric inheritance of parental histones governs epigenome maintenance and embryonic stem cell identity

Modified parental histones are segregated symmetrically to daughter DNA strands during replication and can be inherited through mitosis. How this may sustain the epigenome and cell identity remains unknown. Here we show that transmission of histone-based information during DNA replication maintains epigenome fidelity and embryonic stem cell plasticity. Asymmetric segregation of parental histones H3-H4 in MCM2-2A mutants compromised mitotic inheritance of histone modifications and globally altered the epigenome. This included widespread spurious deposition of repressive modifications, suggesting elevated epigenetic noise. Moreover, H3K9me3 loss at repeats caused derepression and H3K27me3 redistribution across bivalent promoters correlated with misexpression of developmental genes. MCM2-2A mutation challenged dynamic transitions in cellular states across the cell cycle, enhancing naïve pluripotency and reducing lineage priming in G1. Furthermore, developmental competence was diminished, correlating with impaired exit from pluripotency. Collectively, this argues that epigenetic inheritance of histone modifications maintains a correctly balanced and dynamic chromatin landscape able to support mammalian cell differentiation.

Cloning in action: can embryo splitting, induced pluripotency and somatic cell nuclear transfer contribute to endangered species conservation?

The term 'cloning' refers to the production of genetically identical individuals but has meant different things throughout the history of science: a natural means of reproduction in bacteria, a routine procedure in horticulture, and an ever-evolving gamut of molecular technologies in vertebrates. Mammalian cloning can be achieved through embryo splitting, somatic cell nuclear transfer, and most recently, by the use of induced pluripotent stem cells. Several emerging biotechnologies also facilitate the propagation of genomes from one generation to the next whilst bypassing the conventional reproductive processes. In this review, we examine the state of the art of available cloning technologies and their progress in species other than humans and rodent models, in order to provide a critical overview of their readiness and relevance for application in endangered animal conservation.

Cross-activation of FGF, NODAL, and WNT pathways constrains BMP-signaling-mediated induction of the totipotent state in mouse embryonic stem cells

Embryonic stem cells (ESCs) are an attractive model to study the relationship between signaling and cell fates. Cultured mouse ESCs can exist in multiple states resembling distinct stages of early embryogenesis, such as totipotent, pluripotent, primed, and primitive endoderm. The signaling mechanisms regulating the totipotent state and coexistence of these states are poorly understood. Here we identify bone morphogenetic protein (BMP) signaling as an inducer of the totipotent state. However, we discover that BMP's role is constrained by the cross-activation of FGF, NODAL, and WNT pathways. We exploit this finding to enhance the proportion of totipotent cells by rationally inhibiting the cross-activated pathways. Single-cell mRNA sequencing reveals that induction of the totipotent state is accompanied by suppression of primed and primitive endoderm states. Furthermore, reprogrammed totipotent cells we generate in culture resemble totipotent cells of preimplantation embryo. Our findings reveal a BMP signaling mechanism regulating both the totipotent state and heterogeneity of ESCs.

The Wnt/TCF7L1 transcriptional repressor axis drives primitive endoderm formation by antagonizing naive and formative pluripotency

Early during preimplantation development and in heterogeneous mouse embryonic stem cells (mESC) culture, pluripotent cells are specified towards either the primed epiblast or the primitive endoderm (PE) lineage. Canonical Wnt signaling is crucial for safeguarding naive pluripotency and embryo implantation, yet the role and relevance of canonical Wnt inhibition during early mammalian development remains unknown. Here, we demonstrate that transcriptional repression exerted by Wnt/TCF7L1 promotes PE differentiation of mESCs and in preimplantation inner cell mass. Time-series RNA sequencing and promoter occupancy data reveal that TCF7L1 binds and represses genes encoding essential naive pluripotency factors and indispensable regulators of the formative pluripotency program, including Otx2 and Lef1. Consequently, TCF7L1 promotes pluripotency exit and suppresses epiblast lineage formation, thereby driving cells into PE specification. Conversely, TCF7L1 is required for PE specification as deletion of Tcf7l1 abrogates PE differentiation without restraining epiblast priming. Taken together, our study underscores the importance of transcriptional Wnt inhibition in regulating lineage specification in ESCs and preimplantation embryo development as well as identifies TCF7L1 as key regulator of this process.

LINE-1 Retrotransposition Assays in Embryonic Stem Cells

The ongoing mobilization of active non-long terminal repeat (LTR) retrotransposons continues to impact the genomes of most mammals, including humans and rodents. Non-LTR retrotransposons mobilize using an intermediary RNA and a copy-and-paste mechanism termed retrotransposition. Non-LTR retrotransposons are subdivided into long and short interspersed elements (LINEs and SINEs, respectively), depending on their size and autonomy; while active class 1 LINEs (LINE-1s or L1s) encode the enzymatic machinery required to mobilize in cis, active SINEs use the enzymatic machinery of active LINE-1s to mobilize in trans. The mobilization mechanism used by LINE-1s/SINEs was exploited to develop ingenious plasmid-based retrotransposition assays in cultured cells, which typically exploit a reporter gene that can only be activated after a round of retrotransposition. Retrotransposition assays, in cis or in trans, are instrumental tools to study the biology of mammalian LINE-1s and SINEs. In fact, these and other biochemical/genetic assays were used to uncover that endogenous mammalian LINE-1s/SINEs naturally retrotranspose during early embryonic development. However, embryonic stem cells (ESCs) are typically used as a cellular model in these and other studies interrogating LINE-1/SINE expression/regulation during early embryogenesis. Thus, human and mouse ESCs represent an excellent model to understand how active retrotransposons are regulated and how their activity impacts the germline. Here, we describe robust and quantitative protocols to study human/mouse LINE-1 (in cis) and SINE (in trans) retrotransposition using (human and mice) ESCs. These protocols are designed to study the mobilization of active non-LTR retrotransposons in a cellular physiologically relevant context.

Using high throughput screens to predict miscarriages with placental stem cells and long-term stress effects with embryonic stem cells

A problem in developmental toxicology is the massive loss of life from fertilization through gastrulation, and the surprising lack of knowledge of causes of miscarriage. Half to two-thirds of embryos are lost, and environmental and genetic causes are nearly equal. Simply put, it can be inferred that this is a difficult period for normal embryos, but that environmental stresses may cause homeostatic responses that move from adaptive to maladaptive with increasing exposures. At the lower 50% estimate, miscarriage causes greater loss-of-life than all cancers combined or of all cardio- and cerebral-vascular accidents combined. Surprisingly, we do not know if miscarriage rates are increasing or decreasing. Overshadowed by the magnitude of miscarriages, are insufficient data on teratogenic or epigenetic imbalances in surviving embryos and their stem cells. Superimposed on the difficult normal trajectory for peri-gastrulation embryos are added malnutrition, hormonal, and environmental stresses. An overarching hypothesis is that high throughput screens (HTS) using cultured viable reporter embryonic and placental stem cells (e.g., embryonic stem cells [ESC] and trophoblast stem cells [TSC] that report status using fluorescent reporters in living cells) from the pre-gastrulation embryo will most rapidly test a range of hormonal, environmental, nutritional, drug, and diet supplement stresses that decrease stem cell proliferation and imbalance stemness/differentiation. A second hypothesis is that TSC respond with greater sensitivity in magnitude to stress that would cause miscarriage, but ESC are stress-resistant to irreversible stemness loss and are best used to predict long-term health defects. DevTox testing needs more ESC and TSC HTS to model environmental stresses leading to miscarriage or teratogenesis and more research on epidemiology of stress and miscarriage. This endeavor also requires a shift in emphasis on pre- and early gastrulation events during the difficult period of maximum loss by miscarriage.

Transcriptional heterogeneity and cell cycle regulation as central determinants of primitive endoderm priming

During embryonic development cells acquire identity as they proliferate, implying that an intrinsic facet of cell fate choice requires coupling lineage decisions to cell division. How is the cell cycle regulated to promote or suppress heterogeneity and differentiation? We explore this question combining time lapse imaging with single-cell RNA-seq in the contexts of self-renewal, priming, and differentiation of mouse embryonic stem cells (ESCs) towards the Primitive Endoderm (PrE) lineage. Since ESCs are derived from the inner cell mass (ICM) of the mammalian blastocyst, ESCs in standard culture conditions are transcriptionally heterogeneous containing dynamically interconverting subfractions primed for either of the two ICM lineages, Epiblast and PrE. Here, we find that differential regulation of cell cycle can tip the balance between these primed populations, such that naïve ESC culture promotes Epiblast-like expansion and PrE differentiation stimulates the selective survival and proliferation of PrE-primed cells. In endoderm differentiation, this change is accompanied by a counter-intuitive increase in G1 length, also observed in vivo. While fibroblast growth factor/extracellular signal-regulated kinase (FGF/ERK) signalling is a key regulator of ESC differentiation and PrE specification, we find it is not just responsible for ESCs heterogeneity, but also the inheritance of similar cell cycles between sisters and cousins. Taken together, our results indicate a tight relationship between transcriptional heterogeneity and cell cycle regulation in lineage specification, with primed cell populations providing a pool of flexible cell types that can be expanded in a lineage-specific fashion while allowing plasticity during early determination.

Post-gastrulation synthetic embryos generated ex utero from mouse naive ESCs

In vitro cultured stem cells with distinct developmental capacities can contribute to embryonic or extraembryonic tissues after microinjection into pre-implantation mammalian embryos. However, whether cultured stem cells can independently give rise to entire gastrulating embryo-like structures with embryonic and extraembryonic compartments remains unknown. Here, we adapt a recently established platform for prolonged ex utero growth of natural embryos to generate mouse post-gastrulation synthetic whole embryo models (sEmbryos), with both embryonic and extraembryonic compartments, starting solely from naive ESCs. This was achieved by co-aggregating non-transduced ESCs, with naive ESCs transiently expressing Cdx2 or Gata4 to promote their priming toward trophectoderm and primitive endoderm lineages, respectively. sEmbryos adequately accomplish gastrulation, advance through key developmental milestones, and develop organ progenitors within complex extraembryonic compartments similar to E8.5 stage mouse embryos. Our findings highlight the plastic potential of naive pluripotent cells to self-organize and functionally reconstitute and model the entire mammalian embryo beyond gastrulation.

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Advanced synthetic embryos (sEmbryos) self-assembled from ESCs in an ex utero setup

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Naive ESCs give rise to all embryonic and extraembryonic compartments in sEmbryos

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Post-gastrulation stem cell derived sEmbryos develop organ-specific progenitors

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Extraembryonic compartments adequately develop in post-gastrulation whole sEmbryos

The role of BMP4 signaling in trophoblast emergence from pluripotency

The Bone Morphogenetic Protein (BMP) signaling pathway has established roles in early embryonic morphogenesis, particularly in the epiblast. More recently, however, it has also been implicated in development of extraembryonic lineages, including trophectoderm (TE), in both mouse and human. In this review, we will provide an overview of this signaling pathway, with a focus on BMP4, and its role in emergence and development of TE in both early mouse and human embryogenesis. Subsequently, we will build on these in vivo data and discuss the utility of BMP4-based protocols for in vitro conversion of primed vs. naïve pluripotent stem cells (PSC) into trophoblast, and specifically into trophoblast stem cells (TSC). PSC-derived TSC could provide an abundant, reproducible, and ethically acceptable source of cells for modeling placental development.

A critical review on induced totipotent stem cells: Types and methods

Totipotent stem cells are cells with the capacity to form an entire embryo. Many attempts have been made to convert other types of cells to totipotent stem cells which we called induced totipotent stem cells. Various aspects of these cells such as transcriptional and epigenetics networks are unique. By taking advantage of these aspects, efficient methods have been provided to induce totipotent stem cells. Although this advancement is significant, many aspects of induction such as the underlying mechanism remain to be elucidated. On the other hand, embryonic stem cells usually are the source of induction which raise important questions regarding if these methods are induction or promotion of 2C intrinsic totipotent cells in ESC culture. Here, we review the latest mouse progress in underling mechanism of induction of totipotent stem cells. In addition, we follow up on the progress of Blastoids derived from totipotent stem cells.

Filopodia rotate and coil by actively generating twist in their actin shaft

Filopodia are actin-rich structures, present on the surface of eukaryotic cells. These structures play a pivotal role by allowing cells to explore their environment, generate mechanical forces or perform chemical signaling. Their complex dynamics includes buckling, pulling, length and shape changes. We show that filopodia additionally explore their 3D extracellular space by combining growth and shrinking with axial twisting and buckling. Importantly, the actin core inside filopodia performs a twisting or spinning motion which is observed for a range of cell types spanning from earliest development to highly differentiated tissue cells. Non-equilibrium physical modeling of actin and myosin confirm that twist is an emergent phenomenon of active filaments confined in a narrow channel which is supported by measured traction forces and helical buckles that can be ascribed to accumulation of sufficient twist. These results lead us to conclude that activity induced twisting of the actin shaft is a general mechanism underlying fundamental functions of filopodia.

The authors show how tubular surface structures in all cell types, have the ability to twist and perform rotary sweeping motion to explore the extracellular environment. This has implications for migration, sensing and cell communication.

Timely stimulation of early embryo promotes the acquisition of pluripotency

Mouse embryonic stem cells (ESCs) and epiblast stem cells (EpiSCs) are both pluripotent stem cells from early embryos. Another type of pluripotent stem cells, which are similar with EpiSCs and derive from pre-implantation embryos in feeder-free and chemically defined medium containing Activin A and basic fibroblast growth factors (bFGF), is termed as AFSCs. The pluripotency and self-renewal maintenance of ESCs rely on Leukemia inhibitory factor (LIF)/STAT/BMP4/SMAD signaling, while the pluripotency and self-renewal maintenance of EpiSCs and AFSCs rely on bFGF and Activin/Nodal signaling. However, the establishment efficiency of AFSCs lines is low. In this study, we stimulated early embryos by 2i/LIF (CHIR99021 + PD0325901 + LIF) and Activin A + bFGF respectively, to change the cell fate in inner cell mass (ICM). The "fate changed embryos" by 2i/LIF can efficiently produce AFSCs in feeder-free and chemically defined medium, but the efficiency of embryos treated with Activin A + bFGF were poor. The AFSCs from fate-changed embryos share similar molecular characteristics with conventional AFSCs and EpiSCs. Our results suggest that the advanced stimulation of 2i/LIF and the premature stimulation of Activin A + bFGF contribute to capturing the pluripotent stem cells in early embryos, and the FGF/MAPK signaling dominate early embryo development. Our study provides a new approach to capturing pluripotency from pre-implantation embryos.

DUX: One Transcription Factor Controls 2-Cell-like Fate

The double homeobox (Dux) gene, encoding a double homeobox transcription factor, is one of the key drivers of totipotency in mice. Recent studies showed Dux was temporally expressed at the 2-cell stage and acted as a transcriptional activator during zygotic genome activation (ZGA) in embryos. A similar activation occurs in mouse embryonic stem cells, giving rise to 2-cell-like cells (2CLCs). Though the molecular mechanism underlying this expanded 2CLC potency caused by Dux activation has been partially revealed, the regulation mechanisms controlling Dux expression remain elusive. Here, we discuss the latest advancements in the multiple levels of regulation of Dux expression, as well as Dux function in 2CLCs transition, aiming to provide a theoretical framework for understanding the mechanisms that regulate totipotency.

In Vitro Differentiation of Murine Embryonic Stem Cells (ESCs) into Primordial Germ Cell-like Cells (PGCLCs)

The ability to generate primordial germ cell-like cells (PGCLCs) from murine embryonic stem cells (ESCs) has enabled in vitro investigation of the molecular mechanisms regulating this process without the use of a mouse model. Here we describe the procedures from the culture of ESCs to the detection of PGCLCs in the embryoid bodies (spheroids).

Leukemia Inhibitory Factor Stimulates Primitive Endoderm Expansion in the Bovine Inner Cell Mass

Previous work determined that bovine interleukin-6 (IL6) increases inner cell mass (ICM), primitive endoderm (PE), and total cell number in in vitro produced (IVP) bovine blastocysts. Another IL6 family member, leukemia inhibitory factor (LIF), has the potential to produce the same effects of IL6 due to the presence of its receptor in bovine blastocysts. We compared the abilities of LIF and IL6 to increase ICM cell numbers in day 7, 8, and 9 IVP bovine blastocysts. Supplementation with 100 ng/ml LIF from day 5 onward improved blastocyst formation rates on days 7 and 8 similar to what was observed when supplementing 100 ng/ml IL6. However, LIF supplementation did not cause an increase in ICM numbers like was observed after supplementing IL6. On day 9, increases in PE cell numbers were detected after LIF supplementation, but 300 ng/ml LIF was required to achieve the same effect on PE numbers that was observed by providing 100 ng/ml IL6. Collectively, these results show that LIF can mimic at least some of the effects of IL6 in bovine blastocyst.

Capturing Pluripotency and Beyond

During the development of a multicellular organism, the specification of different cell lineages originates in a small group of pluripotent cells, the epiblasts, formed in the preimplantation embryo. The pluripotent epiblast is protected from premature differentiation until exposure to inductive cues in strictly controlled spatially and temporally organized patterns guiding fetus formation. Epiblasts cultured in vitro are embryonic stem cells (ESCs), which recapitulate the self-renewal and lineage specification properties of their endogenous counterparts. The characteristics of totipotency, although less understood than pluripotency, are becoming clearer. Recent studies have shown that a minor ESC subpopulation exhibits expanded developmental potential beyond pluripotency, displaying a characteristic reminiscent of two-cell embryo blastomeres (2CLCs). In addition, reprogramming both mouse and human ESCs in defined media can produce expanded/extended pluripotent stem cells (EPSCs) similar to but different from 2CLCs. Further, the molecular roadmaps driving the transition of various potency states have been clarified. These recent key findings will allow us to understand eutherian mammalian development by comparing the underlying differences between potency network components during development. Using the mouse as a paradigm and recent progress in human PSCs, we review the epiblast's identity acquisition during embryogenesis and their ESC counterparts regarding their pluripotent fates and beyond.

Repression of germline genes by PRC1.6 and SETDB1 in the early embryo precedes DNA methylation-mediated silencing

Silencing of a subset of germline genes is dependent upon DNA methylation (DNAme) post-implantation. However, these genes are generally hypomethylated in the blastocyst, implicating alternative repressive pathways before implantation. Indeed, in embryonic stem cells (ESCs), an overlapping set of genes, including germline "genome-defence" (GGD) genes, are upregulated following deletion of the H3K9 methyltransferase SETDB1 or subunits of the non-canonical PRC1 complex PRC1.6. Here, we show that in pre-implantation embryos and naïve ESCs (nESCs), hypomethylated promoters of germline genes bound by the PRC1.6 DNA-binding subunits MGA/MAX/E2F6 are enriched for RING1B-dependent H2AK119ub1 and H3K9me3. Accordingly, repression of these genes in nESCs shows a greater dependence on PRC1.6 than DNAme. In contrast, GGD genes are hypermethylated in epiblast-like cells (EpiLCs) and their silencing is dependent upon SETDB1, PRC1.6/RING1B and DNAme, with H3K9me3 and DNAme establishment dependent upon MGA binding. Thus, GGD genes are initially repressed by PRC1.6, with DNAme subsequently engaged in post-implantation embryos.

Three-Dimensional Culture Systems for Dissecting Notch Signalling in Health and Disease

Three-dimensional (3D) culture systems opened up new horizons in studying the biology of tissues and organs, modelling various diseases, and screening drugs. Producing accurate in vitro models increases the possibilities for studying molecular control of cell–cell and cell–microenvironment interactions in detail. The Notch signalling is linked to cell fate determination, tissue definition, and maintenance in both physiological and pathological conditions. Hence, 3D cultures provide new accessible platforms for studying activation and modulation of the Notch pathway. In this review, we provide an overview of the recent advances in different 3D culture systems, including spheroids, organoids, and “organ-on-a-chip” models, and their use in analysing the crucial role of Notch signalling in the maintenance of tissue homeostasis, pathology, and regeneration.

Somatic Reprogramming-Above and Beyond Pluripotency

Pluripotent stem cells, having long been considered the fountain of youth, have caught the attention of many researchers from diverse backgrounds due to their capacity for unlimited self-renewal and potential to differentiate into all cell types. Over the past 15 years, the advanced development of induced pluripotent stem cells (iPSCs) has displayed an unparalleled potential for regenerative medicine, cell-based therapies, modeling human diseases in culture, and drug discovery. The transcription factor quartet (Oct4, Sox2, Klf4, and c-Myc) reprograms highly differentiated somatic cells back to a pluripotent state recapitulated embryonic stem cells (ESCs) in different aspects, including gene expression profile, epigenetic signature, and functional pluripotency. With the prior fruitful studies in SCNT and cell fusion experiments, iPSC finds its place and implicates that the differentiated somatic epigenome retains plasticity for re-gaining the pluripotency and further stretchability to reach a totipotency-like state. These achievements have revolutionized the concept and created a new avenue in biomedical sciences for clinical applications. With the advent of 15 years’ progress-making after iPSC discovery, this review is focused on how the current concept is established by revisiting those essential landmark studies and summarizing its current biomedical applications status to facilitate the new era entry of regenerative therapy.

Changes in Cell Morphology and Actin Organization in Embryonic Stem Cells Cultured under Different Conditions

The cellular cytoskeleton provides the cell with a mechanical rigidity that allows mechanical interaction between cells and the extracellular environment. The actin structure plays a key role in mechanical events such as motility or the establishment of cell polarity. From the earliest stages of development, as represented by the ex vivo expansion of naïve embryonic stem cells (ESCs), the critical mechanical role of the actin structure is becoming recognized as a vital cue for correct segregation and lineage control of cells and as a regulatory structure that controls several transcription factors. Naïve ESCs have a characteristic morphology, and the ultrastructure that underlies this condition remains to be further investigated. Here, we investigate the 3D actin cytoskeleton of naïve mouse ESCs using super-resolution optical reconstruction microscopy (STORM). We investigate the morphological, cytoskeletal, and mechanical changes in cells cultured in 2i or Serum/LIF media reflecting, respectively, a homogeneous preimplantation cell state and a state that is closer to embarking on differentiation. STORM imaging showed that the peripheral actin structure undergoes a dramatic change between the two culturing conditions. We also detected micro-rheological differences in the cell periphery between the cells cultured in these two media correlating well with the observed nano-architecture of the ESCs in the two different culture conditions. These results pave the way for linking physical properties and cytoskeletal architecture to cell morphology during early development.

Building Pluripotency Identity in the Early Embryo and Derived Stem Cells

The fusion of two highly differentiated cells, an oocyte with a spermatozoon, gives rise to the zygote, a single totipotent cell, which has the capability to develop into a complete, fully functional organism. Then, as development proceeds, a series of programmed cell divisions occur whereby the arising cells progressively acquire their own cellular and molecular identity, and totipotency narrows until when pluripotency is achieved. The path towards pluripotency involves transcriptome modulation, remodeling of the chromatin epigenetic landscape to which external modulators contribute. Both human and mouse embryos are a source of different types of pluripotent stem cells whose characteristics can be captured and maintained in vitro. The main aim of this review is to address the cellular properties and the molecular signature of the emerging cells during mouse and human early development, highlighting similarities and differences between the two species and between the embryos and their cognate stem cells.

Muscle stem cells and rotator cuff injury

The incidence of reinjury after treatment of rotator cuff tears (RCTs) remains very high despite the variety of nonoperative treatments and the high volume of surgical interventions performed. Muscle stem cells (MuSCs), also known as satellite cells, have risen to the forefront of rotator cuff tear research as a potential adjuvant therapy to aid unsatisfactory surgical outcomes. MuSCs are adult stem cells exhibiting the capacity to proliferate and self-renew, both symmetrically and asymmetrically. As part of this niche, they have been shown to adopt an activated phenotype in response to musculoskeletal injury and decrease their cellular populations during aging, implicating them as key players in both pathologic and normal physiological processes. While commonly connected to the regenerative phase of muscle healing, MuSCs also have the potential to differentiate into adverse morphologies. For instance, if MuSCs differentiate into adipocytes, the ensuing fatty infiltration serves as an obstacle to proper muscle healing and has been associated with the failure of surgical management of RCTs. With the potential to both harm and heal, we have identified MuSCs as a key player in RCT repair. To better understand this dichotomy, the following review will identify key studies regarding the morphology, function, and behavior of MuSCs with respect to RCTs and healing.

Attempts to obtain fully xenogeneic fetuses in rat ↔ mouse model†,‡

The full-term development of the xenogeneic embryo in the uterus of the mother of different species is very restricted and can occur only in certain groups of closely related mammals. In the case of mouse ↔ rat chimeras, the interspecific uterine barrier is less hostile to interspecific chimeric fetuses. In current work, we tested the development of mouse and rat fetuses in uteri of females of the opposite species. We created chimeric mouse ↔ rat blastocysts by injection of mouse embryonic stem cells (ESCs) into eight-cell rat embryos and rat ESCs into eight-cell mouse embryos. Chimeras were transferred to the foster mothers of the opposite species. Despite a huge number of transferred embryos (>1000 in total for both variants), only one live fetus derived solely from the mouse ESCs was isolated at E13.5 from the rat uterus. All other fetuses and newborns were chimeric or were built only from the cells of the recipient embryo. We examined the possible reason for such an outcome and found that the xenogeneic fetuses are eliminated at the perigastrulation stage of development. Thus, we conclude that in the rat ↔ mouse combination even when extraembryonic tissues of the chimeric embryo are composed solely of the cells of the same species as the female to which embryos are transferred, the full-term development of the pure xenogeneic fetus is very unlikely.

Keep the fate: how chromatin regulators safeguard embryonic stem cell identity

Segregation of cells that form the embryo from those that produce the surrounding extra-embryonic tissues is critical for early mammalian development, but the regulatory layers governing these first cell fate decisions remain poorly understood. Recent work in The EMBO Journal identifies two chromatin regulators, Hdac3 and Dax1, that synergistically restrict the developmental potential of mouse embryonic stem cells and act as a lineage barrier to primitive endoderm formation.

All models are wrong, but some are useful: Establishing standards for stem cell-based embryo models

Detailed studies of the embryo allow an increasingly mechanistic understanding of development, which has proved of profound relevance to human disease. The last decade has seen in vitro cultured stem cell-based models of embryo development flourish, which provide an alternative to the embryo for accessible experimentation. However, the usefulness of any stem cell-based embryo model will be determined by how accurately it reflects in vivo embryonic development, and/or the extent to which it facilitates new discoveries. Stringent benchmarking of embryo models is thus an important consideration for this growing field. Here we provide an overview of means to evaluate both the properties of stem cells, the building blocks of most embryo models, as well as the usefulness of current and future in vitro embryo models.

A plug and play microfluidic platform for standardized sensitive low-input chromatin immunoprecipitation

Epigenetic profiling by chromatin immunoprecipitation followed by sequencing (ChIP-seq) has become a powerful tool for genome-wide identification of regulatory elements, for defining transcriptional regulatory networks, and for screening for biomarkers. However, the ChIP-seq protocol for low-input samples is laborious and time-consuming and suffers from experimental variation, resulting in poor reproducibility and low throughput. Although prototypic microfluidic ChIP-seq platforms have been developed, these are poorly transferable as they require sophisticated custom-made equipment and in-depth microfluidic and ChIP expertise, while lacking parallelization. To enable standardized, automated ChIP-seq profiling of low-input samples, we constructed microfluidic PDMS-based plates capable of performing 24 sensitive ChIP reactions within 30 min of hands-on time and 4.5 h of machine-running time. These disposable plates can be conveniently loaded into a widely available controller for pneumatics and thermocycling. In light of the plug and play (PnP) ChIP plates and workflow, we named our procedure PnP-ChIP-seq. We show high-quality ChIP-seq on hundreds to a few thousand of cells for all six post-translational histone modifications that are included in the International Human Epigenome Consortium set of reference epigenomes. PnP-ChIP-seq robustly detects epigenetic differences on promoters and enhancers between naive and more primed mouse embryonic stem cells (mESCs). Furthermore, we used our platform to generate epigenetic profiles of rare subpopulations of mESCs that resemble the two-cell stage of embryonic development. PnP-ChIP-seq allows nonexpert laboratories worldwide to conveniently run robust, standardized ChIP-seq, whereas its high throughput, consistency, and sensitivity pave the way toward large-scale profiling of precious sample types such as rare subpopulations of cells or biopsies.

Human ES Cell Culture Conditions Fail to Preserve the Mouse Epiblast State

Mouse embryonic stem cells (mESCs) and mouse epiblast stem cells (mEpiSCs) are the pluripotent stem cells (PSCs), derived from the inner cell mass (ICM) of preimplantation embryos at embryonic day 3.5 (E3.5) and postimplantation embryos at E5.5-E7.5, respectively. Depending on their environment, PSCs can exist in the so-called naïve (ESCs) or primed (EpiSCs) states. Exposure to EpiSC or human ESC (hESC) culture condition can convert mESCs towards an EpiSC-like state. Here, we show that the undifferentiated epiblast state is however not stabilized in a sustained manner when exposing mESCs to hESC or EpiSC culture condition. Rather, prolonged exposure to EpiSC condition promotes a transition to a primitive streak- (PS-) like state via an unbiased epiblast-like intermediate. We show that the Brachyury-positive PS-like state is likely promoted by endogenous WNT signaling, highlighting a possible species difference between mouse epiblast-like stem cells and human Embryonic Stem Cells.

Interleukin-6 promotes primitive endoderm development in bovine blastocysts

Background

Interleukin-6 (IL6) was recently identified as an embryotrophic factor in bovine embryos, where it acts primarily to mediate inner cell mass (ICM) size. This work explored whether IL6 affects epiblast (EPI) and primitive endoderm (PE) development, the two embryonic lineages generated from the ICM after its formation. Nuclear markers for EPI (NANOG) and PE (GATA6) were used to differentiate the two cell types.

Results

Increases (P < 0.05) in total ICM cell numbers and PE cell numbers were detected in bovine blastocysts at day 8 and 9 post-fertilization after exposure to 100 ng/ml recombinant bovine IL6. Also, IL6 increased (P < 0.05) the number of undifferentiated ICM cells (cells containing both PE and EPI markers). The effects of IL6 on EPI cell numbers were inconsistent. Studies were also completed to explore the importance of Janus kinase 2 (JAK2)-dependent signaling in bovine PE cells. Definitive activation of STAT3, a downstream target for JAK2, was observed in PE cells. Also, pharmacological inhibition of JAK2 decreased (P < 0.05) PE cell numbers.

Conclusions

To conclude, IL6 manipulates ICM development after EPI/PE cell fates are established. The PE cells are the target for IL6, where a JAK-dependent signal is used to regulate PE numbers.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12861-020-00235-z.

Evaluating totipotency using criteria of increasing stringency

Totipotency is the ability of a single cell to give rise to all of the differentiated cell types that build the conceptus, yet how to capture this property in vitro remains incompletely understood. Defining totipotency relies on a variety of assays of variable stringency. Here, we describe criteria to define totipotency. We explain how distinct criteria of increasing stringency can be used to judge totipotency by evaluating candidate totipotent cell types in mice, including early blastomeres and expanded or extended pluripotent stem cells. Our data challenge the notion that expanded or extended pluripotent states harbour increased totipotent potential relative to conventional embryonic stem cells under in vitro and in vivo conditions.

Evaluating totipotency using criteria of increasing stringency

Totipotency is the ability of a single cell to give rise to all of the differentiated cell types that build the conceptus, yet how to capture this property in vitro remains incompletely understood. Defining totipotency relies on a variety of assays of variable stringency. Here, we describe criteria to define totipotency. We explain how distinct criteria of increasing stringency can be used to judge totipotency by evaluating candidate totipotent cell types in mice, including early blastomeres and expanded or extended pluripotent stem cells. Our data challenge the notion that expanded or extended pluripotent states harbour increased totipotent potential relative to conventional embryonic stem cells under in vitro and in vivo conditions.