The role of FGF/Erk signaling in pluripotent cells

Fibroblast growth factor 2 enhances BMSC stemness through ITGA2-dependent PI3K/AKT pathway activation

Bone marrow-derived mesenchymal stem cells (BMSC) are promising cellular reservoirs for treating degenerative diseases, tissue injuries, and immune system disorders. However, the stemness of BMSCs tends to decrease during in vitro cultivation, thereby restricting their efficacy in clinical applications. Consequently, investigating strategies that bolster the preservation of BMSC stemness and maximize therapeutic potential is necessary. Transcriptomic and single-cell sequencing methodologies were used to perform a comprehensive examination of BMSCs with the objective of substantiating the pivotal involvement of fibroblast growth factor 2 (FGF2) and integrin alpha 2 (ITGA2) in stemness regulation. To investigate the impact of these genes on the BMSC stemness in vitro, experimental approaches involving loss and gain of function were implemented. These approaches encompassed the modulation of FGF2 and ITGA2 expression levels via small interfering RNA and overexpression plasmids. Furthermore, we examined their influence on the proliferation and differentiation capacities of BMSCs, along with the expression of stemness markers, including octamer-binding transcription factor 4, Nanog homeobox, and sex determining region Y-box 2. Transcriptomic analyzes successfully identified FGF2 and ITGA2 as pivotal genes responsible for regulating the stemness of BMSCs. Subsequent single-cell sequencing revealed that elevated FGF2 and ITGA2 expression levels within specific stem cell subpopulations are closely associated with stemness maintenance. Moreover, additional in vitro experiments have convincingly demonstrated that FGF2 effectively enhances the BMSC stemness by upregulating ITGA2 expression, a process mediated by the phosphoinositide 3-kinase (PI3K)/protein kinase B (AKT) signaling pathway. This conclusion was supported by the observed upregulation of stemness markers following the induction of FGF2 and ITGA2. Moreover, administration of the BEZ235 pathway inhibitor resulted in the repression of stemness transcription factors, suggesting the substantial involvement of the PI3K/AKT pathway in stemness preservation facilitated by FGF2 and ITGA2. This study elucidates the involvement of FGF2 in augmenting BMSC stemness by modulating ITGA2 and activating the PI3K/AKT pathway. These findings offer valuable contributions to stem cell biology and emphasize the potential of manipulating FGF2 and ITGA2 to optimize BMSCs for therapeutic purposes.

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.

ETV4 and ETV5 Orchestrate FGF-Mediated Lineage Specification and Epiblast Maturation during Early Mouse Development

Cell fate decisions in early mammalian embryos are tightly regulated processes crucial for proper development. While FGF signaling plays key roles in early embryo patterning, its downstream effectors remain poorly understood. Our study demonstrates that the transcription factors Etv4 and Etv5 are critical mediators of FGF signaling in cell lineage specification and maturation in mouse embryos. We show that loss of Etv5 compromises primitive endoderm formation at pre-implantation stages. Furthermore, Etv4/5 deficiency delays naïve pluripotency exit and epiblast maturation, leading to elevated NANOG and reduced OTX2 expression within the blastocyst epiblast. As a consequence of delayed pluripotency progression, Etv4/5 deficient embryos exhibit anterior visceral endoderm migration defects post-implantation, a process essential for coordinated embryonic patterning and gastrulation initiation. Our results demonstrate the successive roles of these FGF signaling effectors in early lineage specification and embryonic body plan establishment, providing new insights into the molecular control of mammalian development.

A novel chemical genetic approach reveals paralog-specific role of ERK1/2 in mouse embryonic stem cell fate control

Introduction: Mouse embryonic stem cell (ESC) self-renewal can be maintained through dual inhibition of GSK3 and MEK kinases. MEK has two highly homologous downstream kinases, extracellular signal-regulated kinase 1 and 2 (ERK1/2). However, the exact roles of ERK1/2 in mouse ESC self-renewal and differentiation remain unclear. Methods: We selectively deleted or inhibited ERK1, ERK2, or both using genetic and chemical genetic approaches combined with small molecule inhibitors. The effects of ERK paralog-specific inhibition on mouse ESC self-renewal and differentiation were then assessed. Results: ERK1/2 were found to be dispensable for mouse ESC survival and self-renewal. The inhibition of both ERK paralogs, in conjunction with GSK3 inhibition, was sufficient to maintain mouse ESC self-renewal. In contrast, selective deletion or inhibition of only one ERK paralog did not mimic the effect of MEK inhibition in promoting mouse ESC self-renewal. Regarding ESC differentiation, inhibition of ERK1/2 prevented mesendoderm differentiation. Additionally, selective inhibition of ERK1, but not ERK2, promoted mesendoderm differentiation. Discussion: These findings suggest that ERK1 and ERK2 have both overlapping and distinct roles in regulating ESC self-renewal and differentiation. This study provides new insights into the molecular mechanisms of ERK1/2 in governing ESC maintenance and lineage commitment, potentially informing future strategies for controlling stem cell fate in research and therapeutic applications.

Naive pluripotent stem cell-based models capture FGF-dependent human hypoblast lineage specification

The hypoblast is an essential extraembryonic tissue set aside within the inner cell mass in the blastocyst. Research with human embryos is challenging. Thus, stem cell models that reproduce hypoblast differentiation provide valuable alternatives. We show here that human naive pluripotent stem cell (PSC) to hypoblast differentiation proceeds via reversion to a transitional ICM-like state from which the hypoblast emerges in concordance with the trajectory in human blastocysts. We identified a window when fibroblast growth factor (FGF) signaling is critical for hypoblast specification. Revisiting FGF signaling in human embryos revealed that inhibition in the early blastocyst suppresses hypoblast formation. In vitro, the induction of hypoblast is synergistically enhanced by limiting trophectoderm and epiblast fates. This finding revises previous reports and establishes a conservation in lineage specification between mice and humans. Overall, this study demonstrates the utility of human naive PSC-based models in elucidating the mechanistic features of early human embryogenesis.

Hidden regulators: the emerging roles of lncRNAs in brain development and disease

Long non-coding RNAs (lncRNAs) have emerged as critical players in brain development and disease. These non-coding transcripts, which once considered as "transcriptional junk," are now known for their regulatory roles in gene expression. In brain development, lncRNAs participate in many processes, including neurogenesis, neuronal differentiation, and synaptogenesis. They employ their effect through a wide variety of transcriptional and post-transcriptional regulatory mechanisms through interactions with chromatin modifiers, transcription factors, and other regulatory molecules. Dysregulation of lncRNAs has been associated with certain brain diseases, including Alzheimer's disease, Parkinson's disease, cancer, and neurodevelopmental disorders. Altered expression and function of specific lncRNAs have been implicated with disrupted neuronal connectivity, impaired synaptic plasticity, and aberrant gene expression pattern, highlighting the functional importance of this subclass of brain-enriched RNAs. Moreover, lncRNAs have been identified as potential biomarkers and therapeutic targets for neurological diseases. Here, we give a comprehensive review of the existing knowledge of lncRNAs. Our aim is to provide a better understanding of the diversity of lncRNA structure and functions in brain development and disease. This holds promise for unravelling the complexity of neurodevelopmental and neurodegenerative disorders, paving the way for the development of novel biomarkers and therapeutic targets for improved diagnosis and treatment.

A guide to ERK dynamics, part 2: downstream decoding

Signaling by the extracellular signal-regulated kinase (ERK) pathway controls many cellular processes, including cell division, death, and differentiation. In this second installment of a two-part review, we address the question of how the ERK pathway exerts distinct and context-specific effects on multiple processes. We discuss how the dynamics of ERK activity induce selective changes in gene expression programs, with insights from both experiments and computational models. With a focus on single-cell biosensor-based studies, we summarize four major functional modes for ERK signaling in tissues: adjusting the size of cell populations, gradient-based patterning, wave propagation of morphological changes, and diversification of cellular gene expression states. These modes of operation are disrupted in cancer and other related diseases and represent potential targets for therapeutic intervention. By understanding the dynamic mechanisms involved in ERK signaling, there is potential for pharmacological strategies that not only simply inhibit ERK, but also restore functional activity patterns and improve disease outcomes.

Signalling pathway crosstalk stimulated by L-proline drives mouse embryonic stem cells to primitive-ectoderm-like cells

The amino acid L-proline exhibits growth factor-like properties during development - from improving blastocyst development to driving neurogenesis in vitro. Addition of 400 μM L-proline to self-renewal medium drives naïve mouse embryonic stem cells (ESCs) to early primitive ectoderm-like (EPL) cells - a transcriptionally distinct primed or partially primed pluripotent state. EPL cells retain expression of pluripotency genes, upregulate primitive ectoderm markers, undergo a morphological change and have increased cell number. These changes are facilitated by a complex signalling network hinging on the Mapk, Fgfr, Pi3k and mTor pathways. Here, we use a factorial experimental design coupled with statistical modelling to understand which signalling pathways are involved in the transition between ESCs and EPL cells, and how they underpin changes in morphology, cell number, apoptosis, proliferation and gene expression. This approach reveals pathways which work antagonistically or synergistically. Most properties were affected by more than one inhibitor, and each inhibitor blocked specific aspects of the naïve-to-primed transition. These mechanisms underpin progression of stem cells across the in vitro pluripotency continuum and serve as a model for pre-, peri- and post-implantation embryogenesis.

A new era of stem cell and developmental biology: from blastoids to synthetic embryos and beyond

Recent discoveries in stem cell and developmental biology have introduced a new era marked by the generation of in vitro models that recapitulate early mammalian development, providing unprecedented opportunities for extensive research in embryogenesis. Here, we present an overview of current techniques that model early mammalian embryogenesis, specifically noting models created from stem cells derived from two significant species: Homo sapiens, for its high relevance, and Mus musculus, a historically common and technically advanced model organism. We aim to provide a holistic understanding of these in vitro models by tracing the historical background of the progress made in stem cell biology and discussing the fundamental underlying principles. At each developmental stage, we present corresponding in vitro models that recapitulate the in vivo embryo and further discuss how these models may be used to model diseases. Through a discussion of these models as well as their potential applications and future challenges, we hope to demonstrate how these innovative advances in stem cell research may be further developed to actualize a model to be used in clinical practice.

Schistosoma mansoni excretory-secretory products induce protein kinase signalling, hyperkinesia, and stem cell proliferation in the opposite sex

Adult male and female schistosomes in copula dwell within human blood vessels and lay eggs that cause the major Neglected Tropical Disease human schistosomiasis. How males and females communicate to each other is poorly understood; however, male-female physical interaction is known to be important. Here, we investigate whether excretory-secretory products (ESPs), released into the external milieu by mature Schistosoma mansoni, might induce responses in the opposite sex. We demonstrate that ESPs adhere to the surface of opposite sex worms inducing the activation of extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) pathways, particularly in the parasite tegument. Furthermore, we show that mature worms stimulated signalling in juvenile worms. Strikingly, we demonstrate that ESPs from the opposite sex promote stem cell proliferation, in an ERK- and p38 MAPK-dependent manner, in the tegument and within the testes of males, and the ovaries and vitellaria of females. Hyperkinesia also occurs following opposite sex ESP exposure. Our findings support the hypothesis that male and female schistosomes may communicate over distance to modulate key processes underlying worm development and disease progression, opening unique avenues for schistosomiasis control.

FGFR-mediated ERK1/2 signaling contributes to mesendoderm and definitive endoderm formation in vitro

The differentiation of human pluripotent stem cells into the SOX17⁺ definitive endoderm (DE) germ layer is important for generating tissues for regenerative medicine. Multiple developmental and stem cell studies have demonstrated that Activin/Nodal signaling is the primary driver of definitive endoderm formation. Here, we uncover that the FGF2-FGFR-ERK1/2 signaling contributes to mesendoderm and SOX17⁺ DE formation. Without ERK1/2 signaling, the Activin/Nodal signaling is insufficient to drive mesendoderm and DE formation. Besides FGF2-FGFR-mediated signaling, IGF1R signaling possibly contributes to the ERK1/2 signaling for DE formation. We identified a temporal relationship between Activin/Nodal-SMAD2 and FGF2-FGFR-ERK1/2 signaling in which Activin/Nodal-SMAD2 participates in the initiation of mesendoderm and DE specification that is followed by increasing activity of FGF2-FGFR-ERK1/2 to facilitate and permit the successful generation of SOX17⁺ DE. Overall, besides the role of Activin/Nodal signaling for DE formation, our findings shed light on the contribution of ERK1/2 signaling for mesendoderm and DE formation.

Deletion of p66Shc Dysregulates ERK and STAT3 Activity in Mouse Embryonic Stem Cells, Enhancing Their Naive-Like Self-Renewal in the Presence of Leukemia Inhibitory Factor

The ShcA adapter protein is necessary for early embryonic development. The role of ShcA in development is primarily attributed to its 52 and 46 kDa isoforms that transduce receptor tyrosine kinase signaling through the extracellular signal regulated kinase (ERK). During embryogenesis, ERK acts as the primary signaling effector, driving fate acquisition and germ layer specification. P66Shc, the largest of the ShcA isoforms, has been observed to antagonize ERK in several contexts; however, its role during embryonic development remains poorly understood. We hypothesized that p66Shc could act as a negative regulator of ERK activity during embryonic development, antagonizing early lineage commitment. To explore the role of p66Shc in stem cell self-renewal and differentiation, we created a p66Shc knockout murine embryonic stem cell (mESC) line. Deletion of p66Shc enhanced basal ERK activity, but surprisingly, instead of inducing mESC differentiation, loss of p66Shc enhanced the expression of core and naive pluripotency markers. Using pharmacologic inhibitors to interrogate potential signaling mechanisms, we discovered that p66Shc deletion permits the self-renewal of naive mESCs in the absence of conventional growth factors, by increasing their responsiveness to leukemia inhibitory factor (LIF). We discovered that loss of p66Shc enhanced not only increased ERK phosphorylation but also increased phosphorylation of Signal transducer and activator of transcription in mESCs, which may be acting to stabilize their naive-like identity, desensitizing them to ERK-mediated differentiation cues. These findings identify p66Shc as a regulator of both LIF-mediated ESC pluripotency and of signaling cascades that initiate postimplantation embryonic development and ESC commitment.

The Role of ATP-Binding Cassette Proteins in Stem Cell Pluripotency

Pluripotent stem cells (PSCs) are highly proliferative cells that can self-renew indefinitely in vitro. Upon receiving appropriate signals, PSCs undergo differentiation and can generate every cell type in the body. These unique properties of PSCs require specific gene expression patterns that define stem cell identity and dynamic regulation of intracellular metabolism to support cell growth and cell fate transitions. PSCs are prone to DNA damage due to elevated replicative and transcriptional stress. Therefore, mechanisms to prevent deleterious mutations in PSCs that compromise stem cell function or increase the risk of tumor formation from becoming amplified and propagated to progenitor cells are essential for embryonic development and for using PSCs including induced PSCs (iPSCs) as a cell source for regenerative medicine. In this review, we discuss the role of the ATP-binding cassette (ABC) superfamily in maintaining PSC homeostasis, and propose how their activities can influence cellular signaling and stem cell fate decisions. Finally, we highlight recent discoveries that not all ABC family members perform only canonical metabolite and peptide transport functions in PSCs; rather, they can participate in diverse cellular processes from genome surveillance to gene transcription and mRNA translation, which are likely to maintain the pristine state of PSCs.

Generation of pulsatile ERK activity in mouse embryonic stem cells is regulated by Raf activity

The extracellular signal-regulated kinase (ERK) is a serine/threonine kinase that is known to regulate cellular events such as cell proliferation and differentiation. The ERK signaling pathway is activated by fibroblast growth factors, and is considered to be indispensable for the differentiation of primitive endoderm cells, not only in mouse preimplantation embryos, but also in embryonic stem cell (ESC) culture. To monitor ERK activity in living undifferentiated and differentiating ESCs, we established EKAREV-NLS-EB5 ESC lines that stably express EKAREV-NLS, a biosensor based on the principle of fluorescence resonance energy transfer. Using EKAREV-NLS-EB5, we found that ERK activity exhibited pulsatile dynamics. ESCs were classified into two groups: active cells showing high-frequency ERK pulses, and inactive cells demonstrating no detectable ERK pulses during live imaging. Pharmacological inhibition of major components in the ERK signaling pathway revealed that Raf plays an important role in determining the pattern of ERK pulses.

Transcription factor ELK1 regulates the expression of histone 3 lysine 9 to affect developmental potential of porcine preimplantation embryos

A series of changes occur in the early embryo that are critical for subsequent development, and the pig is an excellent animal model of human disease, so understanding the regulatory mechanisms of early embryonic development in the pig is of very importance. To find key transcription factors regulating pig early embryonic development, we first profiled the transcriptome of pig early embryos, and confirmed that zygotic gene activation (ZGA) in porcine embryos starts from 4 cell stage. Subsequent enrichment analysis of up-regulated gene motifs during ZGA revealed that the transcription factor ELK1 ranked first. The expression pattern of ELK1 in porcine early embryos was analyzed by immunofluorescence staining and qPCR, and the results showed that the transcript level of ELK1 reached the highest at the 8 cell stage, while the protein level reached the highest at 4 cell stage. To further investigate the effect of ELK1 on early embryo development in pigs, we silenced ELK1 in zygotes and showed that ELK1 silencing significantly reduced cleavage rate, blastocyst rate as well as blastocyst quality. A significant decrease in the expression of the pluripotency gene Oct4 was also observed in blastocysts from the ELK1 silenced group by immunofluorescence staining. Silencing of ELK1 also resulted in decreased H3K9Ac modification and increased H3K9me3 modification at 4 cell stage. To investigate the effect of ELK1 on ZGA, we analyzed transcriptome changes in 4 cell embryos after ELK1 silencing by RNA seq, which revealed that ELK1 silencing resulted in significant differences in the expression of a total of 1953 genes at the 4 cell stage compared with their normal counterparts, including 1106 genes that were significantly upregulated and 847 genes that were significantly downregulated. Through GO and KEGG enrichment, we found that the functions and pathways of down-regulated genes were concentrated in protein synthesis, processing, cell cycle regulation, etc., while the functions of up-regulated genes were focused on aerobic respiration process. In conclusion, this study demonstrates that the transcription factor ELK1 plays an important role in regulation of preimplantation embryo development of pigs and deficiency of ELK1 leads to abnormal epigenetic reprogramming as well as zygotic genome activation, thus adversely affecting embryonic development. This study will provide important reference for the regulation of transcription factors in porcine embryo development.

Optogenetic manipulation identifies the roles of ERK and AKT dynamics in controlling mouse embryonic stem cell exit from pluripotency

ERK and AKT signaling control pluripotent cell self-renewal versus differentiation. ERK pathway activity over time (i.e., dynamics) is heterogeneous between individual pluripotent cells, even in response to the same stimuli. To analyze potential functions of ERK and AKT dynamics in controlling mouse embryonic stem cell (ESC) fates, we developed ESC lines and experimental pipelines for the simultaneous long-term manipulation and quantification of ERK or AKT dynamics and cell fates. We show that ERK activity duration or amplitude or the type of ERK dynamics (e.g., transient, sustained, or oscillatory) alone does not influence exit from pluripotency, but the sum of activity over time does. Interestingly, cells retain memory of previous ERK pulses, with duration of memory retention dependent on duration of previous pulse length. FGF receptor/AKT dynamics counteract ERK-induced pluripotency exit. These findings improve our understanding of how cells integrate dynamics from multiple signaling pathways and translate them into cell fate cues.

The RNA cap methyltransferases RNMT and CMTR1 co-ordinate gene expression during neural differentiation

Regulation of RNA cap formation has potent impacts on gene regulation, controlling which transcripts are expressed, processed and translated into protein. Recently, the RNA cap methyltransferases RNA guanine-7 methyltransferase (RNMT) and cap-specific mRNA (nucleoside-2'-O-)-methyltransferase 1 (CMTR1) have been found to be independently regulated during embryonic stem (ES) cell differentiation controlling the expression of overlapping and distinct protein families. During neural differentiation, RNMT is repressed and CMTR1 is up-regulated. RNMT promotes expression of the pluripotency-associated gene products; repression of the RNMT complex (RNMT-RAM) is required for repression of these RNAs and proteins during differentiation. The predominant RNA targets of CMTR1 encode the histones and ribosomal proteins (RPs). CMTR1 up-regulation is required to maintain the expression of histones and RPs during differentiation and to maintain DNA replication, RNA translation and cell proliferation. Thus the co-ordinate regulation of RNMT and CMTR1 is required for different aspects of ES cell differentiation. In this review, we discuss the mechanisms by which RNMT and CMTR1 are independently regulated during ES cell differentiation and explore how this influences the co-ordinated gene regulation required of emerging cell lineages.

FGF signaling regulates salivary gland branching morphogenesis by modulating cell adhesion

Loss of FGF signaling leads to defects in salivary gland branching, but the mechanisms underlying this phenotype remain largely unknown. We disrupted expression of Fgfr1 and Fgfr2 in salivary gland epithelial cells and found that both receptors function coordinately in regulating branching. Strikingly, branching morphogenesis in double knockouts is restored by Fgfr1 and Fgfr2 (Fgfr1/2) knock-in alleles incapable of engaging canonical RTK signaling, suggesting that additional FGF-dependent mechanisms play a role in salivary gland branching. Fgfr1/2 conditional null mutants showed defective cell-cell and cell-matrix adhesion, both of which have been shown to play instructive roles in salivary gland branching. Loss of FGF signaling led to disordered cell-basement membrane interactions in vivo as well as in organ culture. This was partially restored upon introducing Fgfr1/2 wild-type or signaling alleles that are incapable of eliciting canonical intracellular signaling. Together, our results identify non-canonical FGF signaling mechanisms that regulate branching morphogenesis through cell-adhesion processes.

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.

Molecular versatility during pluripotency progression

A challenge during development is to ensure lineage segregation while preserving plasticity. Using pluripotency progression as a paradigm, we review how developmental transitions are coordinated by redeployments, rather than global resettings, of cellular components. We highlight how changes in response to extrinsic cues (FGF, WNT, Activin/Nodal, Netrin-1), context- and stoichiometry-dependent action of transcription factors (Oct4, Nanog) and reconfigurations of epigenetic regulators (enhancers, promoters, TrxG, PRC) may confer robustness to naïve to primed pluripotency transition. We propose the notion of Molecular Versatility to regroup mechanisms by which molecules are repurposed to exert different, sometimes opposite, functions in close stem cell configurations.

Truncation of IFT80 causes early embryonic loss in Holstein cattle associated with Holstein haplotype 2

Recessive alleles represent genetic risk in populations that have undergone bottleneck events. We present a comprehensive framework for identification and validation of these genetic defects, including haplotype-based detection, variant selection from sequence data, and validation using knockout embryos. Holstein haplotype 2 (HH2), which causes embryonic death, was used to demonstrate the approach. Holstein haplotype 2 was identified using a deficiency-of-homozygotes approach and confirmed to negatively affect conception rate and stillbirths. Five carriers were present in a group of 183 sequenced Holstein bulls selected to maximize the coverage of unique haplotypes. Three variants concordant with haplotype calls were found in HH2: a high-priority frameshift mutation resulting, and 2 low-priority variants (1 synonymous variant, 1 premature stop codon). The frameshift in intraflagellar 80 (IFT80) was confirmed in a separate group of Holsteins from the 1000 Bull Genomes Project that shared no animals with the discovery set. IFT80-null embryos were generated by truncating the IFT80 transcript at exon 2 or 11 using a CRISPR-Cas9 system. Abattoir-derived oocytes were fertilized in vitro, and zygotes were injected at the one-cell stage either with a guide RNA and CAS9 mRNA complex (n = 100) or Cas9 mRNA (control, n = 100) before return to culture, and replicated 3 times. IFT80 is activated at the 8-cell stage, and IFT80-null embryos arrested at this stage of development, which is consistent with data from mouse hypomorphs and HH2 carrier-to-carrier matings. This frameshift in IFT80 on chromosome 1 at 107,172,615 bp (p.Leu381fs) disrupts WNT and hedgehog signaling, and is responsible for the death of homozygous embryos.

The physiological and pathological mechanisms of early embryonic development

Early embryonic development is a complex process. The zygote undergoes several rounds of division to form a blastocyst, and during this process, the zygote undergoes the maternal-to-zygotic transition to gain control of embryonic development and makes two cell fate decisions to differentiate into an embryonic and two extra-embryonic lineages. With the use of new molecular biotechnologies and animal models, we can now further study the molecular mechanisms of early embryonic development and the pathological causes of early embryonic arrest. Here, we first summarize the known molecular regulatory mechanisms of early embryonic development in mice. Then we discuss the pathological factors leading to the early embryonic arrest. We hope that this review will give researchers a relatively complete view of the physiology and pathology of early embryonic development.

A NANOG‐pERK reciprocal regulatory circuit regulates Nanog autoregulation and ERK signaling dynamics

The self‐renewal and differentiation potential of embryonic stem cells (ESCs) is maintained by the regulated expression of core pluripotency factors. Expression levels of the core pluripotency factor Nanog are tightly regulated by a negative feedback autorepression loop. However, it remains unclear how ESCs perceive NANOG levels and execute autorepression. Here, we show that a dose‐dependent induction of Fgfbp1 and Fgfr2 by NANOG activates autocrine‐mediated ERK signaling in Nanog‐high cells to trigger autorepression. pERK recruits NONO to the Nanog locus to repress transcription by preventing POL2 loading. This Nanog autorepression process establishes a self‐perpetuating reciprocal NANOG‐pERK regulatory circuit. We further demonstrate that this reciprocal regulatory circuit induces pERK heterogeneity and ERK signaling dynamics in pluripotent stem cells. Collectively our data suggest that NANOG induces Fgfr2 and Fgfbp1 to activate ERK signaling in Nanog‐high cells to establish a NANOG‐pERK reciprocal regulatory circuit. This circuit regulates ERK signaling dynamics and Nanog autoregulation in pluripotent cells.

Succinate as a New Actor in Pluripotency and Early Development?

Pluripotent cells have been stabilized from pre- and post-implantation blastocysts, representing respectively naïve and primed stages of embryonic stem cells (ESCs) with distinct epigenetic, metabolic and transcriptomic features. Beside these two well characterized pluripotent stages, several intermediate states have been reported, as well as a small subpopulation of cells that have reacquired features of the 2C-embryo (2C-like cells) in naïve mouse ESC culture. Altogether, these represent a continuum of distinct pluripotency stages, characterized by metabolic transitions, for which we propose a new role for a long-known metabolite: succinate. Mostly seen as the metabolite of the TCA, succinate is also at the crossroad of several mitochondrial biochemical pathways. Its role also extends far beyond the mitochondrion, as it can be secreted, modify proteins by lysine succinylation and inhibit the activity of alpha-ketoglutarate-dependent dioxygenases, such as prolyl hydroxylase (PHDs) or histone and DNA demethylases. When released in the extracellular compartment, succinate can trigger several key transduction pathways after binding to SUCNR1, a G-Protein Coupled Receptor. In this review, we highlight the different intra- and extracellular roles that succinate might play in the fields of early pluripotency and embryo development.

New developments in the biology of fibroblast growth factors

The fibroblast growth factor (FGF) family is composed of 18 secreted signaling proteins consisting of canonical FGFs and endocrine FGFs that activate four receptor tyrosine kinases (FGFRs 1-4) and four intracellular proteins (intracellular FGFs or iFGFs) that primarily function to regulate the activity of voltage-gated sodium channels and other molecules. The canonical FGFs, endocrine FGFs, and iFGFs have been reviewed extensively by us and others. In this review, we briefly summarize past reviews and then focus on new developments in the FGF field since our last review in 2015. Some of the highlights in the past 6 years include the use of optogenetic tools, viral vectors, and inducible transgenes to experimentally modulate FGF signaling, the clinical use of small molecule FGFR inhibitors, an expanded understanding of endocrine FGF signaling, functions for FGF signaling in stem cell pluripotency and differentiation, roles for FGF signaling in tissue homeostasis and regeneration, a continuing elaboration of mechanisms of FGF signaling in development, and an expanding appreciation of roles for FGF signaling in neuropsychiatric diseases. This article is categorized under: Cardiovascular Diseases > Molecular and Cellular Physiology Neurological Diseases > Molecular and Cellular Physiology Congenital Diseases > Stem Cells and Development Cancer > Stem Cells and Development.

Comparisons of cell proliferation and cell death from tornaria larva to juvenile worm in the hemichordate Schizocardium californicum

Background

There are a wide range of developmental strategies in animal phyla, but most insights into adult body plan formation come from direct-developing species. For indirect-developing species, there are distinct larval and adult body plans that are linked together by metamorphosis. Some outstanding questions in the development of indirect-developing organisms include the extent to which larval tissue undergoes cell death during the process of metamorphosis and when and where the tissue that will give rise to the adult originates. How do the processes of cell division and cell death redesign the body plans of indirect developers? In this study, we present patterns of cell proliferation and cell death during larval body plan development, metamorphosis, and adult body plan formation, in the hemichordate Schizocardium californium (Cameron and Perez in Zootaxa 3569:79–88, 2012) to answer these questions.

Results

We identified distinct patterns of cell proliferation between larval and adult body plan formation of S. californicum. We found that some adult tissues proliferate during the late larval phase prior to the start of overt metamorphosis. In addition, using an irradiation and transcriptomic approach, we describe a genetic signature of proliferative cells that is shared across the life history states, as well as markers that are unique to larval or juvenile states. Finally, we observed that cell death is minimal in larval stages but begins with the onset of metamorphosis.

Conclusions

Cell proliferation during the development of S. californicum has distinct patterns in the formation of larval and adult body plans. However, cell death is very limited in larvae and begins during the onset of metamorphosis and into early juvenile development in specific domains. The populations of cells that proliferated and gave rise to the larvae and juveniles have a genetic signature that suggested a heterogeneous pool of proliferative progenitors, rather than a set-aside population of pluripotent cells. Taken together, we propose that the gradual morphological transformation of S. californicum is mirrored at the cellular level and may be more representative of the development strategies that characterize metamorphosis in many metazoan animals.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13227-022-00198-1.

From Mice to Men: Generation of Human Blastocyst-Like Structures In Vitro

Advances in the field of stem cell-based models have in recent years lead to the development of blastocyst-like structures termed blastoids. Blastoids can be used to study key events in mammalian pre-implantation development, as they mimic the blastocyst morphologically and transcriptionally, can progress to the post-implantation stage and can be generated in large numbers. Blastoids were originally developed using mouse pluripotent stem cells, and since several groups have successfully generated blastocyst models of the human system. Here we provide a comparison of the mouse and human protocols with the aim of deriving the core requirements for blastoid formation, discuss the models’ current ability to mimic blastocysts and give an outlook on potential future applications.

The canonical FGF-FGFR signaling system at the molecular level

Extracellular signaling molecules, among them the fibroblast growth factors (FGFs), enable cells to communicate with neighboring cells. Such signaling molecules that receive and transmit a signal require specific tyrosine kinase receptors located at the cell surface (fibroblast growth factor receptors, FGFRs). The binding of a signaling molecule to its specific receptor results in receptor dimerization and conformational changes in the cytoplasmic part of the receptor. The conformational changes lead to trans-autophosphorylation of the tyrosine kinase domains of the receptors and subsequently to induction of several downstream signaling pathways and expression of appropriate genes. The signaling pathways activated by FGFs control and coordinate cell behaviors such as cell division, migration, differentiation, and cell death. FGFs and their transmembrane receptors are widely distributed in different tissues and participate in fundamental processes during embryonic, fetal, and adult human life. The human FGF/FGFR family comprises 22 ligands and 4 high affinity receptors. In addition, FGFs bind to low affinity receptors, heparan sulfate proteoglycans at the cell surface. The availability of appropriate ligand/receptor pair, combined with the co-receptor, initiates signaling. Inappropriate FGF/FGFR signaling can cause skeletal disorders, primarily dwarfism, craniofacial malformation syndromes, mood disorders, metabolic disorders, and Kallman syndrome. In addition, aberrations in FGF/FGFR signaling have already been reported in several types of malignant diseases. Knowledge about the molecular mechanisms of FGF/FGFR activation and signaling is necessary to understand the basis of these diseases.

Impact of perlecan, a core component of basement membrane, on regeneration of cartilaginous tissues

As an indispensable component of the extracellular matrix, perlecan (Pln) plays an essential role in cartilaginous tissue function. Although there exist studies suggesting that Pln expressed by cartilaginous tissues is critical for chondrogenesis, few papers have discussed the potential impact Pln may have on cartilage regeneration. In this review, we delineate Pln structure, biomechanical properties, and interactive ligands-which together contribute to the effect Pln has on cartilaginous tissue development. We also review how the signaling pathways of Pln affect cartilage development and scrutinize the potential application of Pln to divisions of cartilage regeneration, spanning vascularization, stem cell differentiation, and biomaterial improvement. The aim of this review is to deepen our understanding of the spatial and temporal interactions that occur between Pln and cartilaginous tissue and ultimately apply Pln in scaffold design to improve cell-based cartilage engineering and regeneration. STATEMENT OF SIGNIFICANCE: As a key component of the basement membrane, Pln plays a critical role in tissue development and repair. Recent findings suggest that Pln existing in the pericellular matrix surrounding mature chondrocytes is actively involved in cartilage regeneration and functionality. We propose that Pln is essential to developing an in vitro matrix niche within biological scaffolds for cartilage tissue engineering.

Human Embryogenesis: A Comparative Perspective

Understanding human embryology has historically relied on comparative approaches using mammalian model organisms. With the advent of low-input methods to investigate genetic and epigenetic mechanisms and efficient techniques to assess gene function, we can now study the human embryo directly. These advances have transformed the investigation of early embryogenesis in nonrodent species, thereby providing a broader understanding of conserved and divergent mechanisms. Here, we present an overview of the major events in human preimplantation development and place them in the context of mammalian evolution by comparing these events in other eutherian and metatherian species. We describe the advances of studies on postimplantation development and discuss stem cell models that mimic postimplantation embryos. A comparative perspective highlights the importance of analyzing different organisms with molecular characterization and functional studies to reveal the principles of early development. This growing field has a fundamental impact in regenerative medicine and raises important ethical considerations.

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.

ZFP451-mediated SUMOylation of SATB2 drives embryonic stem cell differentiation

Here, Urrutia et al. set out to study the mechanism that regulates the choice between pluripotency and differentiation in embryonic stem cells (ESCs). Using biochemical and genomic analyses, the authors identify SUMO2 modification of Satb2 by the E3 ligase Zfp451 as a driver of ESC differentiation.

The establishment of cell fates involves alterations of transcription factor repertoires and repurposing of transcription factors by post-translational modifications. In embryonic stem cells (ESCs), the chromatin organizers SATB2 and SATB1 balance pluripotency and differentiation by activating and repressing pluripotency genes, respectively. Here, we show that conditional Satb2 gene inactivation weakens ESC pluripotency, and we identify SUMO2 modification of SATB2 by the E3 ligase ZFP451 as a potential driver of ESC differentiation. Mutations of two SUMO-acceptor lysines of Satb2 (Satb2^{K →R}) or knockout of Zfp451 impair the ability of ESCs to silence pluripotency genes and activate differentiation-associated genes in response to retinoic acid (RA) treatment. Notably, the forced expression of a SUMO2-SATB2 fusion protein in either Satb2^{K →R} or Zfp451^−/− ESCs rescues, in part, their impaired differentiation potential and enhances the down-regulation of Nanog. The differentiation defect of Satb2^{K →R} ESCs correlates with altered higher-order chromatin interactions relative to Satb2^wt ESCs. Upon RA treatment of Satb2^wt ESCs, SATB2 interacts with ZFP451 and the LSD1/CoREST complex and gains binding at differentiation genes, which is not observed in RA-treated Satb2^{K →R} cells. Thus, SATB2 SUMOylation may contribute to the rewiring of transcriptional networks and the chromatin interactome of ESCs in the transition of pluripotency to differentiation.

A single cell characterisation of human embryogenesis identifies pluripotency transitions and putative anterior hypoblast centre

Following implantation, the human embryo undergoes major morphogenetic transformations that establish the future body plan. While the molecular events underpinning this process are established in mice, they remain unknown in humans. Here we characterise key events of human embryo morphogenesis, in the period between implantation and gastrulation, using single-cell analyses and functional studies. First, the embryonic epiblast cells transition through different pluripotent states and act as a source of FGF signals that ensure proliferation of both embryonic and extra-embryonic tissues. In a subset of embryos, we identify a group of asymmetrically positioned extra-embryonic hypoblast cells expressing inhibitors of BMP, NODAL and WNT signalling pathways. We suggest that this group of cells can act as the anterior singalling centre to pattern the epiblast. These results provide insights into pluripotency state transitions, the role of FGF signalling and the specification of anterior-posterior axis during human embryo development.

Porcine Primordial Germ Cell-Like Cells Generated from Induced Pluripotent Stem Cells Under Different Culture Conditions

Culture conditions regulate the process of pluripotency acquisition and self-renewal. This study aimed to analyse the influence of the in vitro environment on the induction of porcine induced pluripotent stem cell (piPSCs) differentiation into primordial germ cell-like cells (pPGCLCs). piPSC culture with different supplementation strategies (LIF, bFGF, or LIF plus bFGF) promoted heterogeneous phenotypic profiles. Continuous bFGF supplementation during piPSCs culture was beneficial to support a pluripotent state and the differentiation of piPSCs into pPGCLCs. The pPGCLCs were positive for the gene and protein expression of pluripotent and germinative markers. This study can provide a suitable in vitro model for use in translational studies and to help answer numerous remaining questions about germ cells.

Transient Induction and Characterization of Mouse Epiblast-Like Cells from Mouse Embryonic Stem Cells

Mouse embryonic stem cells (mESCs) and mouse epiblast-like cells (mEpiLCs) recapitulate in vitro the epiblast first cell lineage decision, providing a powerful tool to investigate the mechanisms underlying the pluripotent state transition. Here, we describe a defined and robust protocol to transiently induce mEpiLCs from mESCs, together with a concise overview for their unbiased characterization for subsequent downstream applications.

G1-phase progression in pluripotent stem cells

During early embryonic development both the rapid increase in cell number and the expression of genes that control developmental decisions are tightly regulated. Accumulating evidence has indicated that these two seemingly independent processes are mechanistically intertwined. The picture that emerges from studies on the cell cycle of embryonic stem cells is one in which proteins that promote cell cycle progression prevent differentiation and vice versa. Here, we review which transcription factors and signalling pathways play a role in both maintenance of pluripotency as well as cell cycle progression. We will not only describe the mechanism behind their function but also discuss the role of these regulators in different states of mouse pluripotency. Finally, we elaborate on how canonical cell cycle regulators impact on the molecular networks that control the maintenance of pluripotency and lineage specification.

Cadherins in early neural development

During early neural development, changes in signalling inform the expression of transcription factors that in turn instruct changes in cell identity. At the same time, switches in adhesion molecule expression result in cellular rearrangements that define the morphology of the emerging neural tube. It is becoming increasingly clear that these two processes influence each other; adhesion molecules do not simply operate downstream of or in parallel with changes in cell identity but rather actively feed into cell fate decisions. Why are differentiation and adhesion so tightly linked? It is now over 60 years since Conrad Waddington noted the remarkable "Constancy of the Wild Type" (Waddington in Nature 183: 1654-1655, 1959) yet we still do not fully understand the mechanisms that make development so reproducible. Conversely, we do not understand why directed differentiation of cells in a dish is sometimes unpredictable and difficult to control. It has long been suggested that cells make decisions as 'local cooperatives' rather than as individuals (Gurdon in Nature 336: 772-774, 1988; Lander in Cell 144: 955-969, 2011). Given that the cadherin family of adhesion molecules can simultaneously influence morphogenesis and signalling, it is tempting to speculate that they may help coordinate cell fate decisions between neighbouring cells in the embryo to ensure fidelity of patterning, and that the uncoupling of these processes in a culture dish might underlie some of the problems with controlling cell fate decisions ex-vivo. Here we review the expression and function of cadherins during early neural development and discuss how and why they might modulate signalling and differentiation as neural tissues are formed.

Identification of X-chromosomal genes that drive sex differences in embryonic stem cells through a hierarchical CRISPR screening approach

BACKGROUND

X-chromosomal genes contribute to sex differences, in particular during early development, when both X chromosomes are active in females. Double X-dosage shifts female pluripotent cells towards the naive stem cell state by increasing pluripotency factor expression, inhibiting the differentiation-promoting MAP kinase (MAPK) signaling pathway, and delaying differentiation.

RESULTS

To identify the genetic basis of these sex differences, we use a two-step CRISPR screening approach to comprehensively identify X-linked genes that cause the female pluripotency phenotype in murine embryonic stem cells. A primary chromosome-wide CRISPR knockout screen and three secondary screens assaying for different aspects of the female pluripotency phenotype allow us to uncover multiple genes that act in concert and to disentangle their relative roles. Among them, we identify Dusp9 and Klhl13 as two central players. While Dusp9 mainly affects MAPK pathway intermediates, Klhl13 promotes pluripotency factor expression and delays differentiation, with both factors jointly repressing MAPK target gene expression.

CONCLUSIONS

Here, we elucidate the mechanisms that drive sex-induced differences in pluripotent cells and our approach serves as a blueprint to discover the genetic basis of the phenotypic consequences of other chromosomal effects.

Differential Transcriptomes and Methylomes of Trophoblast Stem Cells From Naturally-Fertilized and Somatic Cell Nuclear-Transferred Embryos

Trophoblast stem cells (TSCs) are critical to mammalian embryogenesis by providing the cell source of the placenta. TSCs can be derived from trophoblast cells. However, the efficiency of TSC derivation from somatic cell nuclear transfer (NT) blastocysts is low. The regulatory mechanisms underlying transcription dynamics and epigenetic landscape remodeling during TSC derivation remain elusive. Here, we derived TSCs from the blastocysts by natural fertilization (NF), NT, and a histone deacetylase inhibitor Scriptaid-treated NT (SNT). Profiling of the transcriptomes across the stages of TSC derivation revealed that fibroblast growth factor 4 (FGF4) treatment resulted in many differentially expressed genes (DEGs) at outgrowth and initiated transcription program for TSC formation. We identified 75 transcription factors (TFs) that are continuously upregulated during NF TSC derivation, whose transcription profiles can infer the time course of NF not NT TSC derivation. Most DEGs in NT outgrowth are rescued in SNT outgrowth. The correct time course of SNT TSC derivation is inferred accordingly. Moreover, these TFs comprise an interaction network important to TSC stemness. Profiling of DNA methylation dynamics showed an extremely low level before FGF4 treatment and gradual increases afterward. FGF4 treatment results in a distinct DNA methylation remodeling process committed to TSC formation. We further identified 1,293 CpG islands (CGIs) whose DNA methylation difference is more than 0.25 during NF TSC derivation. The majority of these CGIs become highly methylated upon FGF4 treatment and remain in high levels. This may create a barrier for lineage commitment to restrict embryonic development, and ensure TSC formation. There exist hundreds of aberrantly methylated CGIs during NT TSC derivation, most of which are corrected during SNT TSC derivation. More than half of the aberrantly methylated CGIs before NT TSC formation are inherited from the donor genome. In contrast, the aberrantly methylated CGIs upon TSC formation are mainly from the highly methylated CGIs induced by FGF4 treatment. Functional annotation indicates that the aberrantly highly methylated CGIs play a role in repressing placenta development genes, etc., related to post-implantation development and maintaining TSC pluripotency. Collectively, our findings provide novel insights into the transcription dynamics, DNA methylation remodeling, and the role of FGF4 during TSC derivation.

Co-dependency for MET and FGFR1 in basal triple-negative breast cancers

Triple-negative breast cancer (TNBC) is a heterogeneous disease that lacks both effective patient stratification strategies and therapeutic targets. Whilst elevated levels of the MET receptor tyrosine kinase are associated with TNBCs and predict poor clinical outcome, the functional role of MET in TNBC is still poorly understood. In this study, we utilise an established Met-dependent transgenic mouse model of TNBC, human cell lines and patient-derived xenografts to investigate the role of MET in TNBC tumorigenesis. We find that in TNBCs with mesenchymal signatures, MET participates in a compensatory interplay with FGFR1 to regulate tumour-initiating cells (TICs). We demonstrate a requirement for the scaffold protein FRS2 downstream from both Met and FGFR1 and find that dual inhibition of MET and FGFR1 signalling results in TIC depletion, hindering tumour progression. Importantly, basal breast cancers that display elevated MET and FGFR1 signatures are associated with poor relapse-free survival. Our results support a role for MET and FGFR1 as potential co-targets for anti-TIC therapies in TNBC.

Endogenous suppression of WNT signalling in human embryonic stem cells leads to low differentiation propensity towards definitive endoderm

Low differentiation propensity towards a targeted lineage can significantly hamper the utility of individual human pluripotent stem cell (hPSC) lines in biomedical applications. Here, we use monolayer and micropatterned cell cultures, as well as transcriptomic profiling, to investigate how variability in signalling pathway activity between human embryonic stem cell lines affects their differentiation efficiency towards definitive endoderm (DE). We show that endogenous suppression of WNT signalling in hPSCs at the onset of differentiation prevents the switch from self-renewal to DE specification. Gene expression profiling reveals that this inefficient switch is reflected in NANOG expression dynamics. Importantly, we demonstrate that higher WNT stimulation or inhibition of the PI3K/AKT signalling can overcome the DE commitment blockage. Our findings highlight that redirection of the activity of Activin/NODAL pathway by WNT signalling towards mediating DE fate specification is a vulnerable spot, as disruption of this process can result in poor hPSC specification towards DE.

Integrin β1 coordinates survival and morphogenesis of the embryonic lineage upon implantation and pluripotency transition

At implantation, the embryo establishes contacts with the maternal endometrium. This stage is associated with a high incidence of preclinical pregnancy losses. While the maternal factors underlying uterine receptivity have been investigated, the signals required by the embryo for successful peri-implantation development remain elusive. To explore these, we studied integrin β1 signaling, as embryos deficient for this receptor degenerate at implantation. We demonstrate that the coordinated action of pro-survival signals and localized actomyosin suppression via integrin β1 permits the development of the embryo beyond implantation. Failure of either process leads to developmental arrest and apoptosis. Pharmacological stimulation through fibroblast growth factor 2 (FGF2) and insulin-like growth factor 1 (IGF1), coupled with ROCK-mediated actomyosin inhibition, rescues the deficiency of integrin β1, promoting progression to post-implantation stages. Mutual exclusion between integrin β1 and actomyosin seems to be conserved in the human embryo, suggesting the possibility that these mechanisms could also underlie the transition of the human epiblast from pre- to post-implantation.

FGF19/SOCE/NFATc2 signaling circuit facilitates the self-renewal of liver cancer stem cells

Background & Aims: Liver cancer stem cells (LCSCs) mediate therapeutic resistance and correlate with poor outcomes in patients with hepatocellular carcinoma (HCC). Fibroblast growth factor (FGF)-19 is a crucial oncogenic driver gene in HCC and correlates with poor prognosis. However, whether FGF19 signaling regulates the self-renewal of LCSCs is unknown.

Methods: LCSCs were enriched by serum-free suspension. Self-renewal of LCSCs were characterized by sphere formation assay, clonogenicity assay, sorafenib resistance assay and tumorigenic potential assays. Ca²⁺ image was employed to determine the intracellular concentration of Ca²⁺. Gain- and loss-of function studies were applied to explore the role of FGF19 signaling in the self-renewal of LCSCs.

Results: FGF19 was up-regulated in LCSCs, and positively correlated with certain self-renewal related genes in HCC. Silencing FGF19 suppressed self-renewal of LCSCs, whereas overexpressing FGF19 facilitated CSCs-like properties via activation of FGF receptor (FGFR)-4 in none-LCSCs. Mechanistically, FGF19/FGFR4 signaling stimulated store-operated Ca²⁺ entry (SOCE) through both the PLCγ and ERK1/2 pathways. Subsequently, SOCE-calcineurin signaling promoted the activation and translocation of nuclear factors of activated T cells (NFAT)-c2, which transcriptionally activated the expression of stemness-related genes (e.g., NANOG, OCT4 and SOX2), as well as FGF19. Furthermore, blockade of FGF19/FGFR4-NFATc2 signaling observably suppressed the self-renewal of LCSCs.

Conclusions: FGF19/FGFR4 axis promotes the self-renewal of LCSCs via activating SOCE/NFATc2 pathway; in turn, NFATc2 transcriptionally activates FGF19 expression. Targeting this signaling circuit represents a potential strategy for improving the therapeutic efficacy of HCC.

FGF primes angioblast formation by inducing ETV2 and LMO2 via FGFR1/BRAF/MEK/ERK

It is critical to specify a signal that directly drives the transition that occurs between cell states. However, such inferences are often confounded by indirect intercellular communications or secondary transcriptomic changes due to primary transcription factors. Although FGF is known for its importance during mesoderm-to-endothelium differentiation, its specific role and signaling mechanisms are still unclear due to the confounding factors referenced above. Here, we attempted to minimize the secondary artifacts by manipulating FGF and its downstream mediators with a short incubation time before sampling and protein-synthesis blockage in a low-density angioblastic/endothelial differentiation system. In less than 8 h, FGF started the conversion of KDRlow/PDGFRAlow nascent mesoderm into KDRhigh/PDGFRAlow angioblasts, and the priming by FGF was necessary to endow endothelial formation 72 h later. Further, the angioblastic conversion was mediated by the FGFR1/BRAF/MEK/ERK pathway in mesodermal cells. Finally, two transcription factors, ETV2 and LMO2, were the early direct functional responders downstream of the FGF pathway, and ETV2 alone was enough to complement the absence of FGF. FGF's selective role in mediating the first-step, angioblastic conversion from mesoderm-to-endothelium thus allows for refined control over acquiring and manipulating angioblasts. The noise-minimized differentiation/analysis platform presented here is well-suited for studies on the signaling switches of other mesodermal-lineage fates as well.

Pluripotent stem cells in the research for extraembryonic cell differentiation

Mouse embryonic stem cells (mESCs) are pluripotent stem cell populations derived from the preimplantation embryo and are used to study the differentiation of many types of somatic and germ cells in developing embryos. They are also used to study cell lineages of extraembryonic tissues, such as the trophectoderm (TE) and the primitive endoderm (PrE). mESC cultures are suitable systems for reproducing cellular and molecular events occurring during the differentiation of these cell types, such as changes in gene expression patterns, signaling events, and genome rearrangements although the consistency between the results obtained using mESCs and those of in vivo studies on embryos should be carefully taken into account. Since TE and PrE cells can be induced from mESCs in vitro, mESC cultures are useful systems to study differentiation of these cell lineages during development, if used appropriately. In addition, human pluripotent stem cells (hPSCs), such as human embryonic stem cells (hESCs) and human-induced pluripotent stem cells (hiPSCs), are capable of generating extraembryonic lineages in vitro and are promising tools to study the differentiation of these lineages in the human embryo.

A defined glycosylation regulatory network modulates total glycome dynamics during pluripotency state transition

Embryonic stem cells (ESCs) and epiblast-like cells (EpiLCs) recapitulate in vitro the epiblast first cell lineage decision, allowing characterization of the molecular mechanisms underlying pluripotent state transition. Here, we performed a comprehensive and comparative analysis of total glycomes of mouse ESCs and EpiLCs, revealing that overall glycosylation undergoes dramatic changes from early stages of development. Remarkably, we showed for the first time the presence of a developmentally regulated network orchestrating glycosylation changes and identified polycomb repressive complex 2 (PRC2) as a key component involved in this process. Collectively, our findings provide novel insights into the naïve-to-primed pluripotent state transition and advance the understanding of glycosylation complex regulation during early mouse embryonic development.

TENET: gene network reconstruction using transfer entropy reveals key regulatory factors from single cell transcriptomic data

Accurate prediction of gene regulatory rules is important towards understanding of cellular processes. Existing computational algorithms devised for bulk transcriptomics typically require a large number of time points to infer gene regulatory networks (GRNs), are applicable for a small number of genes and fail to detect potential causal relationships effectively. Here, we propose a novel approach 'TENET' to reconstruct GRNs from single cell RNA sequencing (scRNAseq) datasets. Employing transfer entropy (TE) to measure the amount of causal relationships between genes, TENET predicts large-scale gene regulatory cascades/relationships from scRNAseq data. TENET showed better performance than other GRN reconstructors, in identifying key regulators from public datasets. Specifically from scRNAseq, TENET identified key transcriptional factors in embryonic stem cells (ESCs) and during direct cardiomyocytes reprogramming, where other predictors failed. We further demonstrate that known target genes have significantly higher TE values, and TENET predicted higher TE genes were more influenced by the perturbation of their regulator. Using TENET, we identified and validated that Nme2 is a culture condition specific stem cell factor. These results indicate that TENET is uniquely capable of identifying key regulators from scRNAseq data.

Inhibition of FGF and TGF-β Pathways in hESCs Identify STOX2 as a Novel SMAD2/4 Cofactor

Simple Summary

Signaling pathways are the means by which cells and tissue communicate, orchestrating key events during mammalian development, homeostasis, and disease. During development, signaling determines the identity of cells, and thereby controls morphogenesis and organ specification. Depending on the cellular context, these pathways can exert a broad range of even opposing functions. This is achieved, among other mechanisms, by crosstalk between pathways. Here, we examined how two pathways (the transforming growth factor-β (TGF-β) and the fibroblast growth factor (FGF)) cooperate in the maintenance and cell fate specification of human embryonic stem cells. We used inhibitory molecules for individual pathways on a short time series and analyzed the resulting variation in gene expression. In contrast to our expectations, we did not observe an extended crosstalk between the pathway at the gene regulatory level. However, we discovered STOX2 as a new primary target of the TGF-β signaling pathway. Our results show that STOX2 might act as a novel TGF-β signaling co-factor. Our work will contribute to understand how signaling by the TGF-β is mediated. In the future, these results might help to deepen our understanding of how signaling is propagated.

Abstract

The fibroblast growth factor (FGF) and the transforming growth factor-β (TGF-β) pathways are both involved in the maintenance of human embryonic stem cells (hESCs) and regulate the onset of their differentiation. Their converging functions have suggested that these pathways might share a wide range of overlapping targets. Published studies have focused on the long-term effects (24–48 h) of FGF and TGF-β inhibition in hESCs, identifying direct and indirect target genes. In this study, we focused on the earliest transcriptome changes occurring between 3 and 9 h after FGF and TGF-β inhibition to identify direct target genes only. Our analysis clearly shows that only a handful of target transcripts are common to both pathways. This is surprising in light of the previous literature, and has implications for models of cell signaling in human pluripotent cells. In addition, we identified STOX2 as a novel primary target of the TGF-β signaling pathway. We show that STOX2 might act as a novel SMAD2/4 cofactor. Taken together, our results provide insights into the effect of cell signaling on the transcription profile of human pluripotent cells

Derivation of Intermediate Pluripotent Stem Cells Amenable to Primordial Germ Cell Specification

Dynamic pluripotent stem cell (PSC) states are in vitro adaptations of pluripotency continuum in vivo. Previous studies have generated a number of PSCs with distinct properties. To date, however, no known PSCs have demonstrated dual competency for chimera formation and direct responsiveness to primordial germ cell (PGC) specification, a unique functional feature of formative pluripotency. Here, by modulating fibroblast growth factor (FGF), transforming growth factor β (TGF-β), and WNT pathways, we derived PSCs from mice, horses, and humans (designated as XPSCs) that are permissive for direct PGC-like cell induction in vitro and are capable of contributing to intra- or inter-species chimeras in vivo. XPSCs represent a pluripotency state between naive and primed pluripotency and harbor molecular, cellular, and phenotypic features characteristic of formative pluripotency. XPSCs open new avenues for studying mammalian pluripotency and dissecting the molecular mechanisms governing PGC specification. Our method may be broadly applicable for the derivation of analogous stem cells from other mammalian species.

FGF signaling regulates development by processes beyond canonical pathways

FGFs are key developmental regulators that engage a signal transduction cascade through receptor tyrosine kinases, prominently engaging ERK1/2 but also other pathways. However, it remains unknown whether all FGF activities depend on this canonical signal transduction cascade. To address this question, we generated allelic series of knock-in Fgfr1 and Fgfr2 mouse strains, carrying point mutations that disrupt binding of signaling effectors, and a kinase dead allele of Fgfr2 that broadly phenocopies the null mutant. When interrogated in cranial neural crest cells, we identified discrete functions for signaling pathways in specific craniofacial contexts, but point mutations, even when combined, failed to recapitulate the single or double null mutant phenotypes. Furthermore, the signaling mutations abrogated established FGF-induced signal transduction pathways, yet FGF functions such as cell-matrix and cell-cell adhesion remained unaffected, though these activities did require FGFR kinase activity. Our studies establish combinatorial roles of Fgfr1 and Fgfr2 in development and uncouple novel FGFR kinase-dependent cell adhesion properties from canonical intracellular signaling.