Altered subcellular localization of transcription factor TEAD4 regulates first mammalian cell lineage commitment

Subdiffusive Dynamics Lead to Depleted Particle Densities near Cellular Borders

It has long been known that the complex cellular environment leads to anomalous motion of intracellular particles. At a gross level, this is characterized by mean-squared displacements that deviate from the standard linear profile. Statistical analysis of particle trajectories has helped further elucidate how different characteristics of the cellular environment can introduce different types of anomalousness. A significant majority of this literature has, however, focused on characterizing the properties of trajectories that do not interact with cell borders (e.g., cell membrane or nucleus). Numerous biological processes ranging from protein activation to exocytosis, however, require particles to be near a membrane. This study investigates the consequences of a canonical type of subdiffusive motion, fractional Brownian motion, and its physical analog, generalized Langevin equation dynamics, on the spatial localization of particles near reflecting boundaries. Results show that this type of subdiffusive motion leads to the formation of significant zones of depleted particle density near boundaries and that this effect is independent of the specific model details encoding those dynamics. Rather, these depletion layers are a natural and robust consequence of the anticorrelated nature of motion increments that is at the core of fractional Brownian motion (or alternatively generalized Langevin equation) dynamics. If such depletion zones are present, it would be of profound importance given the wide array of signaling and transport processes that occur near membranes. If not, that would suggest our understanding of this type of anomalous motion may be flawed. Either way, this result points to the need to further investigate the consequences of anomalous particle motions near cell borders from both theoretical and experimental perspectives.

WW Domain-Containing Proteins YAP and TAZ in the Hippo Pathway as Key Regulators in Stemness Maintenance, Tissue Homeostasis, and Tumorigenesis

The Hippo pathway is a conserved signaling pathway originally defined in Drosophila melanogaster two decades ago. Deregulation of the Hippo pathway leads to significant overgrowth in phenotypes and ultimately initiation of tumorigenesis in various tissues. The major WW domain proteins in the Hippo pathway are YAP and TAZ, which regulate embryonic development, organ growth, tissue regeneration, stem cell pluripotency, and tumorigenesis. Recent reports reveal the novel roles of YAP/TAZ in establishing the precise balance of stem cell niches, promoting the production of induced pluripotent stem cells (iPSCs), and provoking signals for regeneration and cancer initiation. Activation of YAP/TAZ, for example, results in the expansion of progenitor cells, which promotes regeneration after tissue damage. YAP is highly expressed in self-renewing pluripotent stem cells. Overexpression of YAP halts stem cell differentiation and yet maintains the inherent stem cell properties. A success in reprograming iPSCs by the transfection of cells with Oct3/4, Sox2, and Yap expression constructs has recently been shown. In this review, we update the current knowledge and the latest progress in the WW domain proteins of the Hippo pathway in relevance to stem cell biology, and provide a thorough understanding in the tissue homeostasis and identification of potential targets to block tumor development. We also provide the regulatory role of tumor suppressor WWOX in the upstream of TGF-β, Hyal-2, and Wnt signaling that cross talks with the Hippo pathway.

Anti-neoplastic effect of mangiferin on human ovarian adenocarcinoma OVCAR8 cells via the regulation of YAP

Ovarian cancer is the most malignant gynecologic neoplasm in women and has the worst prognosis of all cancer types in women based on the 5-year survival rates. A previous study indicated that mangiferin exerts an anti-neoplastic effect on human ovarian cancer cells by targeting Notch3. Additionally, it has been demonstrated that Notch signaling is a functionally important downstream effector of Yes-associated protein (YAP), therefore it was hypothesized that YAP may be involved in the antitumor effect of mangiferin. The present study aimed to further reveal the mangiferin-mediated inhibitory effect on ovarian cancer and investigate the molecular anticancer mechanism of mangiferin. Based on the in vitro data, accompanied with the significantly reduced cell proliferation of mangiferin-treated cells compared with mangiferin-treated YAP-overexpressed cells (P<0.05), YAP expression was identified to be substantially downregulated by mangiferin. In contrast, observations of the cell morphology and apoptotic percentages revealed that the antitumor effect of mangiferin may be reversed by YAP overexpression. Furthermore, decreased levels of migration and invasion were observed in mangiferin-treated cells, which may also be abrogated by YAP overexpression. Thus, these data further demonstrated that mangiferin inhibits metastasis by regulating YAP. Additionally, due to the frequent chemoresistance observed in cisplatin-based chemotherapy, the present study evaluated the cisplatin resistance in OVCAR8 cells and elucidated that mangiferin may sensitize the tumor cells to cisplatin; and this improved sensitization was also abolished by YAP overexpression. These results collectively indicated that YAP was not only closely associated with the anticancer effect of mangiferin, but also mediated drug resistance in tumor. Furthermore, the downregulation of downstream TEA domain transcription factor 4 expression was observed in the mangiferin-treated cells, further validating the inhibitory effect of mangiferin on YAP. In addition, OVCAR8 cell xenograft models revealed that through increasing the sensitivity of a tumor to cisplatin, mangiferin inhibited the growth of a tumor and increased the survival time of tumor xenograft mice. Based on these results, it was concluded that mangiferin may inhibit tumor cell growth and enhance cisplatin-sensitivity in OVCAR8 cells via the regulation of the YAP pathway. Altogether, by targeting YAP and enhancing the response to cisplatin treatment, mangiferin potentially functioned as a novel therapeutic agent in the treatment of ovarian cancer.

TEAD4 overexpression promotes epithelial-mesenchymal transition and associates with aggressiveness and adverse prognosis in head neck squamous cell carcinoma

Background

Deregulated Hippo signaling has been uncovered to be intricately involved in tumorigenesis. Transcriptional factor TEADs serve as key mediators of Hippo signaling and have been increasingly appreciated as putative oncogenes driving cancer initiation and progression. However, its expression pattern and oncogenic role of TEAD4 in head and neck squamous cell carcinoma (HNSCC) remain largely unexplored.

Methods

TEAD4 mRNA expression in HNSCC was determined by data mining and analyses from TCGA dataset and four independent cohorts with transcriptional profiling data publically available. The protein abundance of TEAD4 was measured by immunohistochemistry in 105 primary HNSCC samples and associations between its expression and clinicopathological parameters and patient survival were evaluated. The oncogenic roles of TEAD4 was further determined by 4-nitroquinoline 1-oxide (4NQO)-induced animal model, both knockdown/overexpression assay and TGF-β1-induced epithelia-mesenchymal transition (EMT) in vitro.

Results

Both mRNA and protein abundance of TEAD4 were significantly increased in HNSCC as compared to its non-tumor counterparts. Overexpression of TEAD4 significantly associated with high pathological grade, cervical node metastasis, advanced clinical stage and reduced overall and disease-free survival. In the 4NQO-induced HNSCC mouse model, increased TEAD4 immunostaining was found associated with disease progression. TEAD4 knockdown significantly inhibited cell proliferation, migration and invasion, and induced cell apoptosis in HNSCC cells, while its overexpression resulted in opposite effects and EMT. Moreover, TEAD4 was critically involved in TGF-β1-induced EMT in HNSCC cells.

Conclusions

Our findings reveal that TEAD4 serves as a novel prognostic biomarker and putative oncogene for HNSCC by promoting cell proliferation, migration and invasion, and EMT.

Electronic supplementary material

The online version of this article (10.1186/s12935-018-0675-z) contains supplementary material, which is available to authorized users.

Regulation of energy metabolism during early mammalian development: TEAD4 controls mitochondrial transcription

Early mammalian development is crucially dependent on the establishment of oxidative energy metabolism within the trophectoderm (TE) lineage. Unlike the inner cell mass, TE cells enhance ATP production via mitochondrial oxidative phosphorylation (OXPHOS) and this metabolic preference is essential for blastocyst maturation. However, molecular mechanisms that regulate establishment of oxidative energy metabolism in TE cells are incompletely understood. Here, we show that conserved transcription factor TEAD4, which is essential for pre-implantation mammalian development, regulates this process by promoting mitochondrial transcription. In developing mouse TE and TE-derived trophoblast stem cells (TSCs), TEAD4 localizes to mitochondria, binds to mitochondrial DNA (mtDNA) and facilitates its transcription by recruiting mitochondrial RNA polymerase (POLRMT). Loss of TEAD4 impairs recruitment of POLRMT, resulting in reduced expression of mtDNA-encoded electron transport chain components, thereby inhibiting oxidative energy metabolism. Our studies identify a novel TEAD4-dependent molecular mechanism that regulates energy metabolism in the TE lineage to ensure mammalian development.

The TEA domain family transcription factor TEAD4 represses murine adipogenesis by recruiting the cofactors VGLL4 and CtBP2 into a transcriptional complex

The Hippo signaling pathway is known to play an important role in multiple physiological processes, including adipogenesis. However, whether the downstream components of the Hippo pathway are involved in adipogenesis remains unknown. Here we demonstrate that the TEA domain family (TEAD) transcription factors are essential for adipogenesis in murine 3T3-L1 preadipocytes. Knockdown of TEAD1-4 stimulated adipogenesis and increased the expression of adipocyte markers in these cells. Interestingly, we found that the TEAD4 knockdown-mediated adipogenesis proceeded in a Yes-associated protein (YAP)/TAZ (Wwtr1)-independent manner and that adipogenesis suppression in WT cells involved formation of a ternary complex comprising TEAD4 and the transcriptional cofactors C-terminal binding protein 2 (CtBP2) and vestigial-like family member 4 (VGLL4). VGLL4 acted as an adaptor protein that enhanced the interaction between TEAD4 and CtBP2, and this TEAD4-VGLL4-CtBP2 ternary complex dynamically existed at the early stage of adipogenesis. Finally, we verified that TEAD4 directly targets the promoters of major adipogenesis transcription factors such as peroxisome proliferator-activated receptor γ (PPARγ) and adiponectin, C1Q, and collagen domain-containing (Adipoq) during adipogenesis. These findings reveal critical insights into the role of the TEAD4-VGLL4-CtBP2 transcriptional repressor complex in suppression of adipogenesis in murine preadipocytes.

Building Principles for Constructing a Mammalian Blastocyst Embryo

The self-organisation of a fertilised egg to form a blastocyst structure, which consists of three distinct cell lineages (trophoblast, epiblast and hypoblast) arranged around an off-centre cavity, is unique to mammals. While the starting point (the zygote) and endpoint (the blastocyst) are similar in all mammals, the intervening events have diverged. This review examines and compares the descriptive and functional data surrounding embryonic gene activation, symmetry-breaking, first and second lineage establishment, and fate commitment in a wide range of mammalian orders. The exquisite detail known from mouse embryogenesis, embryonic stem cell studies and the wealth of recent single cell transcriptomic experiments are used to highlight the building principles underlying early mammalian embryonic development.

Crosstalk between YAP/TAZ and Notch Signaling

How the behavior of cells in living tissues is orchestrated according to tissue needs, size, and developmental stage is still poorly understood. Advances in these directions are essential to understand morphogenesis, 'self-organization' phenomena, to build new tissues for regenerative medicine or to reverse the changes in deranged organs, such as in cancer or in genetic disorders. This review outlines a new scenario by which the crosstalk between the Yes-associated protein/transcriptional coactivator with PDZ-binding motif (YAP/TAZ) transcription factors and Notch signaling influences cell self-renewal, stem cell differentiation, cell fate decisions, epithelial-stromal interactions, inflammation, morphogenesis, and large-scale gene oscillations.

Reciprocal regulation of TEAD4 and CCN2 for the trophectoderm development of the bovine blastocyst

The first segregation at the blastocyst stage is the symmetry-breaking event to characterize two cell components; namely, inner cell mass (ICM) and trophectoderm (TE). TEA domain transcription factor 4 (TEAD4) is a well-known regulator to determine TE properties of blastomeres in rodent models. However, the roles of bovine TEAD4 in blastocyst development have been unclear. We here aimed to clarify the mechanisms underlining TE characterization by TEAD4 in bovine blastocysts. We first found that theTEAD4mRNA expression level was greater in TE than in ICM, which was further supported by TEAD4 immunofluorescent staining. Subsequently, we examined the expression patterns of TE-expressed genes;CDX2,GATA2andCCN2, in theTEAD4-knockdown (KD) blastocysts. These expression levels significantly decreased in theTEAD4KD blastocysts compared with controls. Of these downregulated genes, theCCN2expression level decreased the most. We further analyzed the expression levels of TE-expressed genes;CDX2,GATA2andTEAD4in theCCN2KD blastocysts. Strikingly, theCCN2KD blastocysts showed the downregulation ofCDX2,GATA2andTEAD4. Furthermore, the ratio of TE-to-ICM cell numbers in theCCN2KD blastocysts significantly decreased compared to controls. To our knowledge, this is the first study showing the regulation ofCCN2expression thoroughTEAD4in mammalian embryos. Not only that, this study also provides evidence that reciprocal regulation ofTEAD4andCCN2is required for TE development with appropriate gene expression in bovine blastocysts.

Comparative analysis of mouse and human placentae across gestation reveals species-specific regulators of placental development

An increasing body of evidence points to significant spatio-temporal differences in early placental development between mouse and human, but a detailed comparison of placentae in these two species is missing. We set out to compare placentae from both species across gestation, with a focus on trophoblast progenitor markers. We found that CDX2 and ELF5, but not EOMES, are expressed in early post-implantation trophoblast subpopulations in both species. Genome-wide expression profiling of mouse and human placentae revealed clusters of genes with distinct co-expression patterns across gestation. Overall, there was a closer fit between patterns observed in the placentae when the inter-species comparison was restricted to human placentae through gestational week 16 (thus, excluding full-term samples), suggesting that the developmental timeline in mouse runs parallel to the first half of human placental development. In addition, we identified VGLL1 as a human-specific marker of proliferative cytotrophoblast, where it is co-expressed with the transcription factor TEAD4. As TEAD4 is involved in trophectoderm specification in the mouse, we posit a regulatory role for VGLL1 in early events during human placental development.

Transcriptional Regulation and Genes Involved in First Lineage Specification During Preimplantation Development

The successful development from a single-cell zygote into a complex multicellular organism requires precise coordination of multiple cell-fate decisions. The very first of these is lineage specification into the inner cell mass (ICM) and trophectoderm (TE) during mammalian preimplantation development. In mouse embryos, transcription factors (TFs) such as Oct4, Sox2, and Nanog are enriched in cells of ICM, which gives rise to the fetus and yolk sac. Conversely, TFs such as Cdx2 and Eomes become highly upregulated in TE, which contribute to the placenta. Here, we review the current understanding of key transcriptional control mechanisms and genes responsible for these distinct differences during the first cell lineage specification. In particular, we highlight recent insights gained through advances in genome manipulation, live imaging, single-cell transcriptomics, and loss-of-function studies.

Nuclear localization of TEF3-1 promotes cell cycle progression and angiogenesis in cancer

TEF3-1 (transcriptional enhancer factor 3 isoform 1), also known as TEAD4 (TEA domain family member 4), was recently revealed as an oncogenic character in cancer development. However, the underlying molecular pathogenic mechanisms remain undefined. In this paper, we investigated nuclear TEF3-1 could promote G1/S transition in HUVECs, and the expression levels of cyclins and CDKs were upregulated. Additionally, if TEF3-1 was knocked down, the expression of cyclins and CDKs was downregulated while the expression of P21, a negative regulator of the cell cycle, was upregulated. A microarray analysis also confirmed that TEF3-1 overexpression upregulates genes that are related to cell cycle progression and the promotion of angiogenesis. Moreover, we observed that nuclear TEF3-1 was highly expressed during the formation of vascular structures in gastric cancer (GC). Finally, tumor xenograft experiments indicated that, when TEF3-1 was knocked down, tumor growth and angiogenesis were also suppressed. Taken together, these results demonstrate for the first time that TEF3-1 localization to the nucleus stimulates the cell cycle progression in HUVECs and specifically contributes to tumor angiogenesis. Nuclear TEF3-1 in HUVECs may serve as an oncogenic biomarker, and the suppression of TEF3-1 may be a potential target in anti-tumor therapy.

Regulation of the Hippo Pathway Transcription Factor TEAD

The TEAD transcription factor family is best known for transcriptional output of the Hippo signaling pathway and has been implicated in processes such as development, cell growth and proliferation, tissue homeostasis, and regeneration. Our understanding of the functional importance of TEADs has increased dramatically since its initial discovery three decades ago. The majority of our knowledge of TEADs is in the context of Hippo signaling as nuclear DNA-binding proteins passively activated by Yes-associated protein (YAP) and transcriptional activator with PDZ-binding domain (TAZ), transcription coactivators downstream of the Hippo pathway. However, recent studies suggest that TEAD itself is actively regulated. Here, we highlight evidence demonstrating Hippo-independent regulation of TEADs and the potential impacts these studies may have on new cancer therapeutics.

The Hippo signaling pathway provides novel anti-cancer drug targets

The Hippo signaling pathway plays a crucial role in cell proliferation, apoptosis, differentiation, and development. Major effectors of the Hippo signaling pathway include the transcriptional co-activators Yes-associated protein 1 (YAP) and WW domain-containing transcription regulator protein 1 (TAZ). The transcriptional activities of YAP and TAZ are affected by interactions with proteins from many diverse signaling pathways as well as responses to the external environment. High YAP and TAZ activity has been observed in many cancer types, and functional dysregulation of Hippo signaling enhances the oncogenic properties of YAP and TAZ and promotes cancer development. Many biological elements, including mechanical strain on the cell, cell polarity/adhesion molecules, other signaling pathways (e.g., G-protein-coupled receptor, epidermal growth factor receptor, Wnt, Notch, and transforming growth factor β/bone morphogenic protein), and cellular metabolic status, can promote oncogenesis through synergistic association with components of the Hippo signaling pathway. Here, we review the signaling networks that interact with the Hippo signaling pathway and discuss the potential of using drugs that inhibit YAP and TAZ activity for cancer therapy.

Genetic redundancy of GATA factors in the extraembryonic trophoblast lineage ensures the progression of preimplantation and postimplantation mammalian development

GATA transcription factors are implicated in establishing cell fate during mammalian development. In early mammalian embryos, GATA3 is selectively expressed in the extraembryonic trophoblast lineage and regulates gene expression to promote trophoblast fate. However, trophoblast-specific GATA3 function is dispensable for early mammalian development. Here, using dual conditional knockout mice, we show that genetic redundancy of Gata3 with paralog Gata2 in trophoblast progenitors ensures the successful progression of both pre- and postimplantation mammalian development. Stage-specific gene deletion in trophoblasts reveals that loss of both GATA genes, but not either alone, leads to embryonic lethality prior to the onset of their expression within the embryo proper. Using ChIP-seq and RNA-seq analyses, we define the global targets of GATA2/GATA3 and show that they directly regulate a large number of common genes to orchestrate stem versus differentiated trophoblast fate. In trophoblast progenitors, GATA factors directly regulate BMP4, Nodal and Wnt signaling components that promote embryonic-extraembryonic signaling cross-talk, which is essential for the development of the embryo proper. Our study provides genetic evidence that impairment of trophoblast-specific GATA2/GATA3 function could lead to early pregnancy failure.

Summary: During trophoblast development in mice, GATA2 and GATA3 act synergistically by directly regulating a large number of common genes, and together are important to ensure trophoblast lineage progression.

Regulation of Hippo pathway transcription factor TEAD by p38 MAPK-induced cytoplasmic translocation

The Hippo pathway controls organ size and tissue homeostasis, with deregulation leading to cancer. The core Hippo components in mammals are composed of the upstream serine/threonine kinases Mst1/2, MAPK4Ks and Lats1/2. Inactivation of these upstream kinases leads to dephosphorylation, stabilization, nuclear translocation and thus activation of the major functional transducers of the Hippo pathway, YAP and its paralogue TAZ. YAP/TAZ are transcription co-activators that regulate gene expression primarily through interaction with the TEA domain DNA-binding family of transcription factors (TEAD). The current paradigm for regulation of this pathway centres on phosphorylation-dependent nucleocytoplasmic shuttling of YAP/TAZ through a complex network of upstream components. However, unlike other transcription factors, such as SMAD, NF-κB, NFAT and STAT, the regulation of TEAD nucleocytoplasmic shuttling has been largely overlooked. In the present study, we show that environmental stress promotes TEAD cytoplasmic translocation via p38 MAPK in a Hippo-independent manner. Importantly, stress-induced TEAD inhibition predominates YAP-activating signals and selectively suppresses YAP-driven cancer cell growth. Our data reveal a mechanism governing TEAD nucleocytoplasmic shuttling and show that TEAD localization is a critical determinant of Hippo signalling output.

Notch and Hippo signaling converge on Strawberry Notch 1 (Sbno1) to synergistically activate Cdx2 during specification of the trophectoderm

The first binary cell fate decision occurs at the morula stage and gives rise to two distinct types of cells that constitute the trophectoderm (TE) and inner cell mass (ICM). The cell fate determinant, Cdx2, is induced in TE cells and plays an essential role in their differentiation and maintenance. Notch and Hippo signaling cascades are assumed to converge onto regulatory elements of Cdx2, however, the underlying molecular mechanisms are largely unknown. Here, we show involvement of Strawberry Notch1 (Sbno1), a novel chromatin factor of the helicase superfamily 2, during preimplantation development. Sbno1 knockout embryos die at the preimplantation stage without forming a blastocoel, and Cdx2 is not turned on even though both Yap and Tead4 reside normally in nuclei. Accordingly, Sbno1 acts on the trophectoderm-enhancer (TEE) of Cdx2, ensuring its robust and synergistic activation by the Yap/Tead4 and NICD/Rbpj complexes. Interestingly, this synergism is enhanced when cells are mechanically stretched, which might reflect that TE cells are continuously stretched by the expanding ICM and blastocoel cavity. In addition, the histone chaperone, FACT (FAcilitates Chromatin Transcription) physically interacts with Sbno1. Our data provide new evidence on TE specification, highlighting unexpected but essential functions of the highly conserved chromatin factor, Sbno1.

Position- and Hippo signaling-dependent plasticity during lineage segregation in the early mouse embryo

The segregation of the trophectoderm (TE) from the inner cell mass (ICM) in the mouse blastocyst is determined by position-dependent Hippo signaling. However, the window of responsiveness to Hippo signaling, the exact timing of lineage commitment and the overall relationship between cell commitment and global gene expression changes are still unclear. Single-cell RNA sequencing during lineage segregation revealed that the TE transcriptional profile stabilizes earlier than the ICM and prior to blastocyst formation. Using quantitative Cdx2-eGFP expression as a readout of Hippo signaling activity, we assessed the experimental potential of individual blastomeres based on their level of Cdx2-eGFP expression and correlated potential with gene expression dynamics. We find that TE specification and commitment coincide and occur at the time of transcriptional stabilization, whereas ICM cells still retain the ability to regenerate TE up to the early blastocyst stage. Plasticity of both lineages is coincident with their window of sensitivity to Hippo signaling.

DOI:http://dx.doi.org/10.7554/eLife.22906.001

In female mammals, conception is a complex process that involves several stages. First, an egg is released from the ovary and travels along a tube called the oviduct, where sperm from a male may fertilize it. If the egg is fertilized, the newly formed embryo moves into the womb, where it will then implant into the walls. In mice, it takes around four days for the embryo to implant and during this time, the cells in the embryo divide several times and start to specialize to form distinct cell types called lineages.

The first two lineages to form are known as the inner cell mass and the trophectoderm. The inner cell mass forms a ball of cells within the embryo and contains the precursors of all cells that build the animal’s body. The trophectoderm forms a layer that surrounds the inner cell mass and will become part of the placenta (the organ that supplies the embryo with nutrients while it is in the womb). The embryo can organize these lineages without any instructions from the mother. However, it is still not clear when the cells start to differ from each other, and when they ‘commit’ to stay in these lineages.

Cells in the inner cell mass and trophectoderm have different gene expression profiles, meaning that many genes display different levels of activity in these two lineages. Posfai et al. use a technique called single-cell RNA sequencing to analyse gene activity as the inner cell mass and trophectoderm form in mouse embryos. By measuring changes in gene activity, it is possible to track their development and show which genes change expression levels when each lineage specifies and commits.

The experiments reveal that the inner cell mass and trophectoderm lineages develop at different times. As the inner cell mass forms, cells adopt the inner cell mass ‘identity’ before they commit to remaining in this lineage, revealing a window of time where different signals could still change the fate of the cells. However, when the early trophectoderm cells show the first signs of specialization, they also commit to their new identity at the same time.

These findings suggest that the different timings at which these cell lineages form might provide embryos with the means to organize their own cells. An important future challenge is to understand exactly how the cells commit to their fate.

DOI:http://dx.doi.org/10.7554/eLife.22906.002

Transcriptome analyses of rhesus monkey preimplantation embryos reveal a reduced capacity for DNA double-strand break repair in primate oocytes and early embryos

Preimplantation embryogenesis encompasses several critical events including genome reprogramming, zygotic genome activation (ZGA), and cell-fate commitment. The molecular basis of these processes remains obscure in primates in which there is a high rate of embryo wastage. Thus, understanding the factors involved in genome reprogramming and ZGA might help reproductive success during this susceptible period of early development and generate induced pluripotent stem cells with greater efficiency. Moreover, explaining the molecular basis responsible for embryo wastage in primates will greatly expand our knowledge of species evolution. By using RNA-seq in single and pooled oocytes and embryos, we defined the transcriptome throughout preimplantation development in rhesus monkey. In comparison to archival human and mouse data, we found that the transcriptome dynamics of monkey oocytes and embryos were very similar to those of human but very different from those of mouse. We identified several classes of maternal and zygotic genes, whose expression peaks were highly correlated with the time frames of genome reprogramming, ZGA, and cell-fate commitment, respectively. Importantly, comparison of the ZGA-related network modules among the three species revealed less robust surveillance of genomic instability in primate oocytes and embryos than in rodents, particularly in the pathways of DNA damage signaling and homology-directed DNA double-strand break repair. This study highlights the utility of monkey models to better understand the molecular basis for genome reprogramming, ZGA, and genomic stability surveillance in human early embryogenesis and may provide insights for improved homologous recombination-mediated gene editing in monkey.

Hypoxia Directs Human Extravillous Trophoblast Differentiation in a Hypoxia-Inducible Factor-Dependent Manner

Villous cytotrophoblasts are epithelial stem cells of the early human placenta, able to differentiate either into syncytiotrophoblasts in floating chorionic villi or extravillous trophoblasts (EVTs) at the anchoring villi. The signaling pathways regulating differentiation into these two lineages are incompletely understood. The bulk of placental growth and development in the first trimester occurs under low oxygen tension. One major mechanism by which oxygen regulates cellular function is through the hypoxia-inducible factor (HIF), a transcription factor complex stabilized under low oxygen tension to mediate cellular responses, including cell fate decisions. HIF is known to play a role in trophoblast differentiation in rodents; however, its role in human trophoblast differentiation is poorly understood. Using RNA profiling of sorted populations of primary first-trimester trophoblasts, we evaluated the first stage of EVT differentiation, the transition from epidermal growth factor receptor⁺ villous cytotrophoblasts into human leukocyte antigen-G⁺ proximal column EVT (pcEVT) and identified hypoxia as a major pcEVT-associated pathway. Using primary cytotrophoblasts, we determined that culture in low oxygen directs differentiation preferentially toward human leukocyte antigen-G⁺ pcEVT, and that an intact HIF complex is required for this process. Finally, using global RNA profiling, we identified integrin-linked kinase and associated cytoskeletal remodeling and adhesion to be among HIF-dependent pcEVT-associated signaling pathways. Taken together, we propose that oxygen regulates EVT differentiation through HIF-dependent modulation of various cell adhesion and morphology-related pathways.

Gene Expression Noise Enhances Robust Organization of the Early Mammalian Blastocyst

A critical event in mammalian embryo development is construction of an inner cell mass surrounded by a trophoectoderm (a shell of cells that later form extraembryonic structures). We utilize multi-scale, stochastic modeling to investigate the design principles responsible for robust establishment of these structures. This investigation makes three predictions, each supported by our quantitative imaging. First, stochasticity in the expression of critical genes promotes cell plasticity and has a critical role in accurately organizing the developing mouse blastocyst. Second, asymmetry in the levels of noise variation (expression fluctuation) of Cdx2 and Oct4 provides a means to gain the benefits of noise-mediated plasticity while ameliorating the potentially detrimental effects of stochasticity. Finally, by controlling the timing and pace of cell fate specification, the embryo temporally modulates plasticity and creates a time window during which each cell can continually read its environment and adjusts its fate. These results suggest noise has a crucial role in maintaining cellular plasticity and organizing the blastocyst.

A critical event in mammalian embryo development is construction of a mass of embryonic stem cells surrounded by a distinct shell that later forms the placenta along with other structures. Despite sustained investigation, multiple hypotheses for what is responsible for this organization persist and it remains unclear what is responsible for the robust organization (remarkable ability for embryos to pattern correctly) of these structures. Here, we utilize multi-scale, stochastic modeling along with fluorescence imaging to investigate the factors that contribute to the incredible robustness of this organizational process. Results point to two factors that contribute to this robustness: 1) the timing and pace of cell fate specification and 2) stochastic gene regulatory effects. The former creates a window of time during which each cell can continually read their environment and adjust their gene expressions (and consequently fate) in response to dynamic rearrangements of cells arising from cell divisions and motions. The latter improves cell plasticity, providing the capability for cells to adjust to changes in their local environment. Fluorescence imaging results demonstrate that the magnitude and structure of gene expression variations match those predicted to promote organizational robustness.

Effects of downregulating TEAD4 transcripts by RNA interference on early development of bovine embryos

Transcription factor TEA domain family transcription factor 4 (Tead4) is one of the key factors involved in the differentiation of the trophectoderm (TE) in murine embryos. However, knowledge on the roles of TEAD4 in preimplantation development during bovine embryos is currently limited. This study examined the transcript and protein expression patterns of TEAD4 and attempted to elucidate the functions of TEAD4 during bovine preimplantation development using RNA interference. TEAD4 mRNA was found to be upregulated between the 16-cell and morula stages, and nuclear localization of the TEAD4 protein was detected at the morula stage, as well as in subsequent developmental stages. TEAD4 downregulation did not affect embryonic development until the blastocyst stage, and TEAD4-downregulated embryos were capable of forming the TE under both 5% and 21% O₂ conditions. Results of gene expression analysis showed that TEAD4 downregulation did not affect the expression levels of POU class 5 transcription factor 1 (OCT-4), NANOG, caudal-type homeobox 2 (CDX2), GATA binding protein 3 (GATA3), and interferon-tau (IFNT). In conclusion, TEAD4 might be dispensable for development until the blastocyst stage and TE differentiation in bovine embryos.

Stem cell insights into human trophoblast lineage differentiation

BACKGROUND

The human placenta is vital for fetal development, yet little is understood about how it forms successfully to ensure a healthy pregnancy or why this process is inadequate in 1 in 10 pregnancies, leading to miscarriage, intrauterine growth restriction or preeclampsia. Trophoblasts are placenta-specific epithelial cells that maximize nutrient exchange. All trophoblast lineages are thought to arise from a population of trophoblast stem cells (TSCs). However, whilst the isolation of murine TSC has led to an explosion in understanding murine placentation, the isolation of an analogous human TSC has proved more difficult. Consequently, alternative methods of studying human trophoblast lineage development have been employed, including human embryonic stem cells (hESCs), induced pluripotent stem cells (iPS) and transformed cell lines; but what do these proxy models tell us about what is happening during early placental development?

OBJECTIVE AND RATIONALE

In this systematic review, we evaluate current approaches to understanding human trophoblast lineage development in order to collate and refine these models and inform future approaches aimed at establishing human TSC lines.

SEARCH METHODS

To ensure all relevant articles were analysed, an unfiltered search of Pubmed, Embase, Scopus and Web of Science was conducted for 25 key terms on the 13th May 2016. In total, 47 313 articles were retrieved and manually filtered based on non-human, non-English, non-full text, non-original article and off-topic subject matter. This resulted in a total of 71 articles deemed relevant for review in this article.

OUTCOMES

Candidate human TSC populations have been identified in, and isolated from, both the chorionic membrane and villous tissue of the placenta, but further investigation is required to validate these as 'true' human TSCs. Isolating human TSCs from blastocyst trophectoderm has not been successful in humans as it was in mice, although recently the first reported TSC line (USFB6) was isolated from an eight-cell morula. In lieu of human TSC lines, trophoblast-like cells have been induced to differentiate from hESCs and iPS. However, differentiation in these model systems is difficult to control, culture conditions employed are highly variable, and the extent to which they accurately convey the biology of 'true' human TSCs remains unclear, particularly as a consensus has not been met among the scientific community regarding which characteristics a human TSC must possess.

WIDER IMPLICATIONS

Human TSC models have the potential to revolutionize our understanding of trophoblast differentiation, allowing us to make significant gains in understanding the underlying pathology of pregnancy disorders and to test potential therapeutic interventions on cell function in vitro. In order to do this, a collaborative effort is required to establish the criteria that define a human TSC to confirm the presence of human TSCs in both primary isolates and to determine how accurately trophoblast-like cells derived from current model systems reflect trophoblast from primary tissue. The in vitro systems currently used to model early trophoblast lineage formation have provided insights into early human placental formation but it is unclear whether these trophoblast-like cells are truly representative of primary human trophoblast. Consequently, continued refinement of current models, and standardization of culture protocols is essential to aid our ability to identify, isolate and propagate 'true' human TSCs from primary tissue.

YAP1 and TAZ Control Pancreatic Cancer Initiation in Mice by Direct Up-regulation of JAK-STAT3 Signaling

BACKGROUND & AIMS

Pancreatitis is the most important risk factor for pancreatic ductal adenocarcinoma (PDAC). Pancreatitis predisposes to PDAC because it induces a process of acinar cell reprogramming known as acinar-to-ductal metaplasia (ADM)-a precursor of pancreatic intraepithelial neoplasia lesions that can progress to PDAC. Mutations in KRAS are found at the earliest stages of pancreatic tumorigenesis, and it appears to be a gatekeeper to cancer progression. We investigated how mutations in KRAS cooperate with pancreatitis to promote pancreatic cancer progression in mice.

METHODS

We generated mice carrying conditional alleles of Yap1 and Taz and disrupted Yap1 and Taz using a Cre-lox recombination strategy in adult mouse pancreatic acinar cells (Yap1fl/fl;Tazfl/fl;Ela1-CreERT2). We crossed these mice with LSL-KrasG12D mice, which express a constitutively active form of KRAS after Cre recombination. Pancreatic tumor initiation and progression were analyzed after chemically induced pancreatitis. We analyzed pancreatic tissues from patients with pancreatitis or PDAC by immunohistochemistry.

RESULTS

Oncogenic activation of KRAS in normal, untransformed acinar cells in the pancreatic tissues of mice resulted in increased levels of pancreatitis-induced ADM. Expression of the constitutive active form of KRAS in this system led to activation of the transcriptional regulators YAP1 and TAZ; their function was required for pancreatitis-induced ADM in mice. The JAK-STAT3 pathway was a downstream effector of KRAS signaling via YAP1 and TAZ. YAP1 and TAZ directly mediated transcriptional activation of several genes in the JAK-STAT3 signaling pathway; this could be a mechanism by which acinar cells that express activated KRAS become susceptible to inflammation.

CONCLUSIONS

We identified a mechanism by which oncogenic KRAS facilitates ADM and thereby generates the cells that initiate neoplastic progression. This process involves activation of YAP1 and TAZ in acinar cells, which up-regulate JAK-STAT3 signaling to promote development of PDAC in mice.

Establishment of bovine embryonic stem cells after knockdown of CDX2

Bovine embryonic stem cells (bESCs) have not been successfully established yet. One reason could be that CDX2, as the trophectoderm regulator, expresses in bovine inner cell mass (ICM), which probably becomes a technical barrier for maintaining the pluripotency of bESCs in vitro. We hypothesized that CDX2 knockdown (CDX2-KD) could remove such negative effort, which will be helpful for capturing complete and permanent capacity of pluripotency. Expression and localization of pluripotent genes were not affected in CDX2-KD blastocysts. The CDX2-KD bESCs grew into monolayers on feeder layer. Pluripotent genes expressed at an improved levels and lasted longer time in CDX2-KD bESCs, along with down-regulation of DNA methylation on promoters of both OCT4 and SOX2. The cystic structure typical for trophoblast cells did not show during culturing CDX2-KD bESCs. CDX2-KD bESC-derived Embryoid bodies showed with compact morphology and with the improved levels of differentiations in three germ layers. CDX2-KD bESCs still carried the capacity of forming teratomas with three germ layers after long-term culture. In summary, CDX2 in bovine ICM was inducer of trophoblast lineage with negative effect on maintenance of pluripotency of bESCs. Precise regulation CDX2 expression to switch on/off will be studied next for application on establishment of bESCs.

Roles of ERα during mouse trophectoderm lineage differentiation: revealed by antagonist and agonist of ERα

During mouse early embryogenesis, blastomeres increase in number by the morula stage. Among them, the outer cells are polarized and differentiated into trophectoderm (TE), while the inner cells remain unpolarized and give rise to inner cell mass (ICM). TE provides an important liquid environment for ICM development. In spite of extensive research, the molecular mechanisms underlying TE formation are still obscure. In order to investigate the roles of estrogen receptor α (ERα) in this course, mouse 8-cell embryos were collected and cultured in media containing ERα specific antagonist MPP and/or agonist PPT. The results indicated that MPP treatment inhibits blastocyst formation in a dose-dependent manner, while PPT, at proper concentration, promotes the cavitation ratio of mouse embryos. Immunofluorescence staining results showed that MPP significantly decreased the nuclear expression of CDX2 in morula, but no significant changes of OCT4 were observed. Moreover, after MPP treatment, the expression levels of the genes related to TE specification, Tead4, Gata3 and Cdx2, were significantly reduced. Overall, these results indicated that ERα might affect mouse embryo cavitation by regulating TE lineage differentiation.

Yap1 is dispensable for self-renewal but required for proper differentiation of mouse embryonic stem (ES) cells

Yap1 is a transcriptional co-activator of the Hippo pathway. The importance of Yap1 in early cell fate decision during embryogenesis has been well established, though its role in embryonic stem (ES) cells remains elusive. Here, we report that Yap1 plays crucial roles in normal differentiation rather than self-renewal of ES cells. Yap1-depleted ES cells maintain undifferentiated state with a typical colony morphology as well as robust alkaline phosphatase activity. These cells also retain comparable levels of the core pluripotent factors, such as Pou5f1 and Sox2, to the levels in wild-type ES cells without significant alteration of lineage-specific marker genes. Conversely, overexpression of Yap1 in ES cells promotes nuclear translocation of Yap1, resulting in disruption of self-renewal and triggering differentiation by up-regulating lineage-specific genes. Moreover, Yap1-deficient ES cells show impaired induction of lineage markers during differentiation. Collectively, our data demonstrate that Yap1 is a required factor for proper differentiation of mouse ES cells, while remaining dispensable for self-renewal.

Analysis of Hippo and TGFβ signaling in polarizing epithelial cells and mouse embryos

The Hippo signaling pathway is involved in numerous biological events ranging from early development to organogenesis and when disrupted, impacts various human diseases including cancer. The Hippo pathway also interacts with and controls the activity of other signaling pathways such as the TGFβ/Smad pathway, in which Hippo pathway activity influences the subcellular localization of Smad transcription factors. Here, we describe techniques for examining crosstalk between Hippo and TGFβ signaling in polarizing mammary epithelial cells. In addition, we provide detailed methods for analyzing the subcellular localization of the Hippo pathway effectors, Taz and Yap using both in vitro cultured epithelial cells and in vivo in pregastrulation mouse embryos.

Lineage Segregation in the Totipotent Embryo

After a spermatozoon enters an oocyte, maternal factors accumulated in the oocyte reprogram the genomes of the terminally differentiated oocyte and spermatozoon epigenetically and turn the zygote into a totipotent cell, with the capacity to differentiate into all types of somatic cells in a highly organized manner and generate the entire organism, a feature referred to as totipotency. Differentiation of the first lineage begins after three cleavages, when the early embryo compacts and becomes polarized, followed by segregation of the first lineages--the inner cell mass (ICM) and the trophectoderm (TE). To date, a full understanding of the molecular mechanisms that underlie the establishment of totipotency and the ICM/TE lineage segregation remains unclear. In this review, we discuss recent findings in the mechanism of transcriptional regulation networks and signaling pathways in the first lineage separation in the totipotent mouse embryo.

Discordant Growth of Monozygotic Twins Starts at the Blastocyst Stage: A Case Study

Discordant growth is a common complication of monochorionic/diamniotic pregnancies; in approximately 50% of cases, the cause is unknown. The case presented here suggests that discordant growth of monozygotic twins could start during preimplantation development. Two inner cell masses (ICMs) within the same blastocyst may originate in uneven splitting of a single “parental” ICM, or the two ICMs may be formed independently de novo. We studied the transcriptomes of two morphologically distinct ICMs within a single blastocyst using high-resolution RNA sequencing. The data indicated that the two ICM were at different stages of development; one was in the earliest stages of lineage commitment, while the other had already differentiated into epiblast and primitive endoderm. IGF1-mediated signaling is likely to play a key role in ICM growth and to be the major driver behind these differences.

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Two ICMs within the same blastocyst were at different stages of development

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IGF1-mediated signaling is likely to be the major driver behind these differences

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The expression pattern of YAP1 is different in human embryos from in the mouse

The first two cell-fate decisions of preimplantation mouse embryo development are not functionally independent

During mouse preimplantation embryo development, three distinct cell lineages are formed, represented by the differentiating trophectoderm (TE), primitive endoderm (PrE) and the pluripotent epiblast (EPI). Classically, lineage derivation has been presented as a two-step process whereby outer TE cells are first segregated from inner-cell mass (ICM), followed by ICM refinement into either the PrE or EPI. As ICM founders can be produced following the fourth or fifth cleavage divisions, their potential to equally contribute to EPI and PrE is contested. Thus, modelling the early sequestration of ICM founders from TE-differentiation after the fourth cleavage division, we examined ICM lineage contribution of varying sized cell clones unable to initiate TE-differentiation. Such TE-inhibited ICM cells do not equally contribute to EPI and PrE and are significantly biased to form EPI. This bias is not caused by enhanced expression of the EPI marker Nanog, nor correlated with reduced apical polarity but associated with reduced expression of PrE-related gene transcripts (Dab2 and Lrp2) and down-regulation of plasma membrane associated Fgfr2. Our results favour a unifying model were the three cell lineages are guided in an integrated, yet flexible, fate decision centred on relative exposure of founder cells to TE-differentiative cues.

Making the first decision: lessons from the mouse

Pre-implantation development encompasses a period of 3-4 days over which the mammalian embryo has to make its first decision: to separate the pluripotent inner cell mass (ICM) from the extra-embryonic epithelial tissue, the trophectoderm (TE). The ICM gives rise to tissues mainly building the body of the future organism, while the TE contributes to the extra-embryonic tissues that support embryo development after implantation. This review provides an overview of the cellular and molecular mechanisms that control the critical aspects of this first decision, and highlights the role of critical events, namely zytotic genome activation, compaction, polarization, asymmetric cell divisions, formation of the blastocyst cavity and expression of key transcription factors.

Increased TEAD4 expression and nuclear localization in colorectal cancer promote epithelial-mesenchymal transition and metastasis in a YAP-independent manner

Dysregulation of the Hippo pathway occurs in a variety of cancers and often correlates with a poor prognosis. To further explore the potential role of Hippo pathway dysregulation in tumor development and progression, we investigated its downstream transcription factor TEAD4 in colorectal cancer (CRC). Increased expression and nuclear localization of TEAD4 were found in a significant portion of CRC tissues, in association with metastasis and a poor prognosis. In CRC cells, TEAD4 knockdown induced the mesenchymal-epithelial transition and decreased cell mobility in vitro and metastasis in vivo. Microarray analysis revealed that TEAD4 promoted cell adhesion and upregulated the epithelial-mesenchymal transition-related transcriptome in CRC cells. Vimentin was identified as a new direct target gene mediating TEAD4 function in CRC cells, whereby forced vimentin expression markedly reversed TEAD4-knockdown-induced cell morphological changes and decreased mobility. Interestingly, rescued expression of both WT TEAD4 and a Y429H mutant can reverse the mesenchymal-epithelial transition and increase vimentin expression, cell mobility and metastatic potential in TEAD4-knockdown CRC cells. The discrepant expression of YAP and TEAD4 in CRC tissues, the rescue ability of TEAD4 mutant defect in YAP binding and no effect on vimentin expression by YAP knockdown in CRC cells, all implicated a YAP-independent manner of TEAD4 function in CRC. Furthermore, vimentin positively correlated and CDH1 reversely correlated with the level of TEAD4 in CRC tissues and xenograft tumors. Our results suggest that TEAD4 nuclear expression can serve as a biomarker for CRC progression and poor prognosis. The transcription factor TEAD4 regulates a pro-metastasis transcription program in a YAP-independent manner in CRC, thus providing a novel mechanism of TEAD4 transcriptional regulation and its oncogenic role in CRC, independently of the Hippo pathway.

Regulation of mitochondrial function and cellular energy metabolism by protein kinase C-λ/ι: a novel mode of balancing pluripotency

Pluripotent stem cells (PSCs) contain functionally immature mitochondria and rely upon high rates of glycolysis for their energy requirements. Thus, altered mitochondrial function and promotion of aerobic glycolysis are key to maintain and induce pluripotency. However, signaling mechanisms that regulate mitochondrial function and reprogram metabolic preferences in self-renewing versus differentiated PSC populations are poorly understood. Here, using murine embryonic stem cells (ESCs) as a model system, we demonstrate that atypical protein kinase C isoform, PKC lambda/iota (PKCλ/ι), is a key regulator of mitochondrial function in ESCs. Depletion of PKCλ/ι in ESCs maintains their pluripotent state as evident from germline offsprings. Interestingly, loss of PKCλ/ι in ESCs leads to impairment in mitochondrial maturation, organization, and a metabolic shift toward glycolysis under differentiating condition. Our mechanistic analyses indicate that a PKCλ/ι-hypoxia-inducible factor 1α-PGC1α axis regulates mitochondrial respiration and balances pluripotency in ESCs. We propose that PKCλ/ι could be a crucial regulator of mitochondrial function and energy metabolism in stem cells and other cellular contexts.

Soybean transcription factor ORFeome associated with drought resistance: a valuable resource to accelerate research on abiotic stress resistance

BACKGROUND

Whole genome sequencing provides the most comprehensive collection of an organism's genetic information. The availability of complete genome sequences is expected to dramatically deliver a high impact on biology. However, to achieve this impact in the area of crop improvement, significant efforts are still required on functional genomics, including the areas of gene annotation, cloning, expression profiling, and functional validation.

RESULTS

Here we report our efforts in generating the first transcription factor (TF) open reading frame (ORF)eome resource associated with drought resistance in soybean (Glycine max), a major oil/protein crop grown worldwide. This study provides a highly annotated soybean TF-ORFeome associated with drought resistance. It contains information from experimentally verified protein-coding sequences (CDS), expression profiling under several abiotic stresses (drought, salinity, dehydration and ABA), and computationally predicted protein subcellular localization and cis-regulatory elements (CREs) analysis. All the information is available to plant researchers through a freely accessible and user-friendly database, Soybean Knowledge Base (SoyKB).

CONCLUSIONS

The soybean TF-ORFeome provides a valuable public resource for functional genomics studies, especially in the area of plant abiotic stresses. It will accelerate findings in the areas of abiotic stresses and lead to the generation of crops with enhanced resistance to multiple stresses.

CHD1 acts via the Hmgpi pathway to regulate mouse early embryogenesis

The protein CHD1 is a member of the family of ATPase-dependent chromatin remodeling factors. CHD1, which recognizes trimethylated histone H3 lysine 4, has been implicated in transcriptional activation in organisms ranging from yeast to humans. It is required for pre-mRNA maturation, maintenance of mouse embryonic stem cell pluripotency and rapid growth of the mouse epiblast. However, the function(s) of CHD1 in mouse preimplantation embryos has not yet been examined. Here, we show that loss of CHD1 function led to embryonic lethality after implantation. In mouse embryos in which Chd1 was targeted by siRNA microinjection, the expression of the key regulators of cell fate specification Pou5f1 (also known as Oct4), Nanog and Cdx2 was dramatically decreased, starting at mid-preimplantation gene activation (MGA). Moreover, expression of Hmgpi and Klf5, which regulate Pou5f1, Nanog and Cdx2, was also significantly suppressed at zygotic gene activation (ZGA). Suppression of Hmgpi expression in Chd1-knockdown embryos continued until the blastocyst stage, whereas suppression of Klf5 expression was relieved by the morula stage. Next, we rescued HMGPI expression via Hmgpi mRNA microinjection in Chd1-knockdown embryos. Consequently, Pou5f1, Nanog and Cdx2 expression was restored at MGA and live offspring were recovered. These findings indicate that CHD1 plays important roles in mouse early embryogenesis via activation of Hmgpi at ZGA.

YAP and TAZ: a nexus for Hippo signaling and beyond

The Hippo pathway is a potent regulator of cellular proliferation, differentiation, and tissue homeostasis. Here we review the regulatory mechanisms of the Hippo pathway and discuss the function of Yes-associated protein (YAP)/transcriptional coactivator with a PDZ-binding domain (TAZ), the prime mediators of the Hippo pathway, in stem cell biology and tissue regeneration. We highlight their activities in both the nucleus and the cytoplasm and discuss their role as a signaling nexus and integrator of several other prominent signaling pathways such as the Wnt, G protein-coupled receptor (GPCR), epidermal growth factor (EGF), bone morphogenetic protein (BMP)/transforming growth factor beta (TGFβ), and Notch pathways.

Cell signaling and transcription factors regulating cell fate during formation of the mouse blastocyst

The first cell fate decisions during mammalian development establish tissues essential for healthy pregnancy. The mouse has served as a valuable model for discovering pathways regulating the first cell fate decisions because of the ease with which early embryos can be recovered and the availability of an arsenal of classical and emerging methods for manipulating gene expression. We summarize the major pathways that govern the first cell fate decisions in mouse development. This knowledge serves as a paradigm for exploring how emergent properties of a self-organizing system can dynamically regulate gene expression and cell fate plasticity. Moreover, it brings to light the processes that establish healthy pregnancy and ES cells. We also describe unsolved mysteries and new technologies that could help to overcome experimental challenges in the field.

Position- and polarity-dependent Hippo signaling regulates cell fates in preimplantation mouse embryos

During the preimplantation stage, mouse embryos establish two cell lineages by the time of early blastocyst formation: the trophectoderm (TE) and the inner cell mass (ICM). Historical models have proposed that the establishment of these two lineages depends on the cell position within the embryo (e.g., the positional model) or cell polarization along the apicobasal axis (e.g., the polarity model). Recent findings have revealed that the Hippo signaling pathway plays a central role in the cell fate-specification process: active and inactive Hippo signaling in the inner and outer cells promote ICM and TE fates, respectively. Intercellular adhesion activates, while apicobasal polarization suppresses Hippo signaling, and a combination of these processes determines the spatially regulated activation of the Hippo pathway in 32-cell-stage embryos. Therefore, there is experimental evidence in favor of both positional and polarity models. At the molecular level, phosphorylation of the Hippo-pathway component angiomotin at adherens junctions (AJs) in the inner (apolar) cells activates the Lats protein kinase and triggers Hippo signaling. In the outer cells, however, cell polarization sequesters Amot from basolateral AJs and suppresses activation of the Hippo pathway. Other mechanisms, including asymmetric cell division and Notch signaling, also play important roles in the regulation of embryonic development. In this review, I discuss how these mechanisms cooperate with the Hippo signaling pathway during cell fate-specification processes.

Transcription factor AP-2γ induces early Cdx2 expression and represses HIPPO signaling to specify the trophectoderm lineage

Cell fate decisions are fundamental to the development of multicellular organisms. In mammals the first cell fate decision involves segregation of the pluripotent inner cell mass and the trophectoderm, a process regulated by cell polarity proteins, HIPPO signaling and lineage-specific transcription factors such as CDX2. However, the regulatory mechanisms that operate upstream to specify the trophectoderm lineage have not been established. Here we report that transcription factor AP-2γ (TFAP2C) functions as a novel upstream regulator of Cdx2 expression and position-dependent HIPPO signaling in mice. Loss- and gain-of-function studies and promoter analysis revealed that TFAP2C binding to an intronic enhancer is required for activation of Cdx2 expression during early development. During the 8-cell to morula transition TFAP2C potentiates cell polarity to suppress HIPPO signaling in the outside blastomeres. TFAP2C depletion triggered downregulation of PARD6B, loss of apical cell polarity, disorganization of F-actin, and activation of HIPPO signaling in the outside blastomeres. Rescue experiments using Pard6b mRNA restored cell polarity but only partially corrected position-dependent HIPPO signaling, suggesting that TFAP2C negatively regulates HIPPO signaling via multiple pathways. Several genes involved in regulation of the actin cytoskeleton (including Rock1, Rock2) were downregulated in TFAP2C-depleted embryos. Inhibition of ROCK1 and ROCK2 activity during the 8-cell to morula transition phenocopied TFAP2C knockdown, triggering a loss of position-dependent HIPPO signaling and decrease in Cdx2 expression. Altogether, these results demonstrate that TFAP2C facilitates trophectoderm lineage specification by functioning as a key regulator of Cdx2 transcription, cell polarity and position-dependent HIPPO signaling.

Adaptive mechanisms controlling uterine spiral artery remodeling during the establishment of pregnancy

Implantation of the embryo into the uterus triggers the initiation of hemochorial placentation. The hemochorial placenta facilitates the acquisition of maternal resources required for embryo/fetal growth. Uterine spiral arteries form the nutrient supply line for the placenta and fetus. This vascular conduit undergoes gestation stage-specific remodeling directed by maternal natural killer cells and embryo-derived invasive trophoblast lineages. The placentation site, including remodeling of the uterine spiral arteries, is shaped by environmental challenges. In this review, we discuss the cellular participants controlling pregnancy-dependent uterine spiral artery remodeling and mechanisms responsible for their development and function.

Predicting the human epigenome from DNA motifs

The epigenome is established and maintained by the site-specific recruitment of chromatin-modifying enzymes and their cofactors. Identifying the cis elements that regulate epigenomic modification is critical for understanding the regulatory mechanisms that control gene expression patterns. We present Epigram, an analysis pipeline that predicts histone modification and DNA methylation patterns from DNA motifs. The identified cis elements represent interactions with the site-specific DNA-binding factors that establish and maintain epigenomic modifications. We cataloged the cis elements in embryonic stem cells and four derived lineages and found numerous motifs that have location preference, such as at the center of H3K27ac or at the edges of H3K4me3 and H3K9me3, which provides mechanistic insight about the shaping of the epigenome. The Epigram pipeline and predictive motifs are at http://wanglab.ucsd.edu/star/epigram/.

Characterization of the transcriptional activation domains of human TEF3-1 (transcription enhancer factor 3 isoform 1)

TEF3-1 (transcription enhancer factor 3 isoform 1) is a human transcriptional factor, which has a N-terminal TEA/ATTS domain supposedly for DNA binding and C-terminal PRD and STY domains for transcriptional activation. Taking advantage of the efficient reporter design of yeast two-hybrid system, we characterized the TEF3-1 domains in activating gene expression. Previously study usually mentioned that the C-terminal domain of TEF3-1 has the transcriptional activity, however, our data shows that the peptides TEF3-11-66 and TEF3-1197-434 functioned as two independent activation domains, suggesting that N-terminal domain of TEF3-1 also has transcriptional activation capacity. Additionally, more deletions of amino acids 197-434 showed that only the peptides TEF3-1197-265 contained the minimum sequences for the C-terminal transcriptional activation domain. The protein structure is predicted to contain a helix-turn-helix structure in TEF3-11-66 and four β sheets in TEF3-1197-265. Finally, after the truncated fragments of TEF3-1 were expressed in HUVEC cells, the whole TEF3-1 and the two activation domains could increase F-actin stress fiber, cell proliferation, migration and targeted gene expression. Further analysis and characterization of the activation domains in TEF3-1 may broaden our understanding of the gene involved in angiogenesis and other pathological processes.