Rho differentially regulates the Hippo pathway by modulating the interaction between Amot and Nf2 in the blastocyst

Maternal exposure to hyperbaric oxygen at the preimplantation stages increases apoptosis and ectopic Cdx2 expression and decreases Oct4 expression in mouse blastocysts via Nrf2-Notch1 upregulation and Nf2 downregulation

BACKGROUND

The environmental oxygen tension has been reported to impact the blastocyst quality and cell numbers in the inner cell mass (ICM) during human and murine embryogenesis. While the molecular mechanisms leading to increased ICM cell numbers and pluripotency gene expression under hypoxia have been deciphered, it remains unknown which regulatory pathways caused the underweight fetal body and overweight placenta after maternal exposure to hyperbaric oxygen (HBO).

RESULTS

The blastocysts from the HBO-exposed pregnant mice revealed significantly increased signals of reactive oxygen species (ROS) and nuclear Nrf2 staining, decreased Nf2 and Oct4 expression, increased nuclear Tp53bp1 and active caspase-3 staining, and ectopic nuclear signals of Cdx2, Yap, and the Notch1 intracellular domain (N1ICD) in the ICM. In the ICM of the HBO-exposed blastocysts, both Nf2 cDNA microinjection and Nrf2 shRNA microinjection significantly decreased the ectopic nuclear expression of Cdx2, Tp53bp1, and Yap whereas increased Oct4 expression, while Nrf2 shRNA microinjection also significantly decreased Notch1 mRNA levels and nuclear expression of N1ICD and active caspase-3.

CONCLUSION

We show for the first time that maternal exposure to HBO at the preimplantation stage induces apoptosis and impairs ICM cell specification via upregulating Nrf2-Notch1-Cdx2 expression and downregulating Nf2-Oct4 expression.

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

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

Inflammation modulates intercellular adhesion and mechanotransduction in human epidermis via ROCK2

Aberrant mechanotransduction and compromised epithelial barrier function are associated with numerous human pathologies including inflammatory skin disorders. However, the cytoskeletal mechanisms regulating inflammatory responses in the epidermis are not well understood. Here we addressed this question by inducing a psoriatic phenotype in human keratinocytes and reconstructed human epidermis using a cytokine stimulation model. We show that the inflammation upregulates the Rho-myosin II pathway and destabilizes adherens junctions (AJs) promoting YAP nuclear entry. The integrity of cell-cell adhesion but not the myosin II contractility per se is the determinative factor for the YAP regulation in epidermal keratinocytes. The inflammation-induced disruption of AJs, increased paracellular permeability, and YAP nuclear translocation are regulated by ROCK2, independently from myosin II activation. Using a specific inhibitor KD025, we show that ROCK2 executes its effects via cytoskeletal and transcription-dependent mechanisms to shape the inflammatory response in the epidermis.

Leveraging substrate stiffness to promote stem cell asymmetric division via mechanotransduction-polarity protein axis and its Bayesian regression analysis

Asymmetric division of stem cells is an evolutionarily conserved process in multicellular organisms responsible for maintaining cellular fate diversity. Symmetric-asymmetric division pattern of mesenchymal stem cells (MSC) is regulated by both biochemical and biophysical cues. However, modulation of mechanotransduction pathway by varying scaffold properties and their adaptation to control stem cell division fate is not widely established. In present study, we explored the interplay between the mechanotrasduction pathway and polarity protein complex in stem cell asymmetry under varied biophysical stimuli. We hypothesize that variation of scaffold stiffness will impart mechanical stimulus and control the cytoskeleton assembly through RhoA, which will lead to further downstream activation of polarity-related cell signalling and asymmetric division of MSC. To establish the hypothesis, umbilical cord derived MSC were cultured on PCL/collagen scaffolds with varied stiffness and expressions of several important genes (viz. YAP, TAZ, LATS1, LATS2, Par3, Par6, PRKC1 (homolog of aPKC) and RhoA) and biomarkers (viz. YAP, TAZ, F-actin, Numb) were assessed. SVM polarity index was employed to understand the polarization status of the MSC cultured on varied scaffold stiffness. Further, the Bayesian logistic regression model was employed for classifying the asymmetric division of MSC cultured on different scaffold stiffness which showed 91% accuracy. Present study emphasizes the vital role of scaffold properties in modulating the mechanotransduction signalling pathway of MSC and provides mechanistic basis for adopting facile method to control stem cell division pattern towards improving tissue engineering outcome.

Yes-associated protein reacts differently in vascular smooth muscle cells under different intensities of mechanical stretch

Vascular smooth muscle cells (VSMCs) are stromal cells of the vascular wall and are continually exposed to mechanical signals. The loss of VSMCs is closely related to the occurrence of many vascular diseases, such as aortic aneurysms and aortic dissection. The proliferation and apoptosis of VSMCs are mechanically stimulated. Yes-associated protein (YAP), one of the core components of the Hippo pathway, plays a key role in the response of VSMCs to mechanical signals. In this study, we tested the impact of different intensities of mechanical stretch on the proliferation and apoptosis of VSMCs, as well as YAP. We tested VSMCs’ proliferation and apoptosis and YAP reaction via immunocytochemistry, western blotting, CCK-8 and flow cytometric analysis. We found that 10% elongation could increase the phosphorylation of YAP and prevent it from entering the nucleus, as well as inhibit cell proliferation and promote apoptosis. However, 15% elongation reduced YAP phosphorylation and promoted its nuclear entry, thereby promoting cell proliferation and inhibiting apoptosis. Accordingly, YAP knockdown suppressed the phenotype of VMSCs induced by 15% elongation. Taken together, YAP regulates proliferation and apoptosis of VSMCs differently under different intensity of mechanical stretch. Mechanical stretch with appropriate intensity can promote the proliferation and inhibit apoptosis of VSMCs by activating YAP.

A tale of two cell-fates: role of the Hippo signaling pathway and transcription factors in early lineage formation in mouse preimplantation embryos

In mammals, the first cell-fate decision occurs during preimplantation embryo development when the inner cell mass (ICM) and trophectoderm (TE) lineages are established. The ICM develops into the embryo proper, while the TE lineage forms the placenta. The underlying molecular mechanisms that govern lineage formation involve cell-to-cell interactions, cell polarization, cell signaling and transcriptional regulation. In this review, we will discuss the current understanding regarding the cellular and molecular events that regulate lineage formation in mouse preimplantation embryos with an emphasis on cell polarity and the Hippo signaling pathway. Moreover, we will provide an overview on some of the molecular tools that are used to manipulate the Hippo pathway and study cell-fate decisions in early embryos. Lastly, we will provide exciting future perspectives on transcriptional regulatory mechanisms that modulate the activity of the Hippo pathway in preimplantation embryos to ensure robust lineage segregation.

Roles and mechanisms of YAP/TAZ in orthodontic tooth movement

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ) are transcriptional coactivators encoded by paratactic homologous genes, shuttle-crossing between cytoplasm and nucleus to regulate the gene expression and cell behavior and standing at the center place of the sophisticated regulatory networking of mechanotransduction. Orthodontic tooth movement (OTM) is a process in which extracellular mechanical stimuli are transformed into intracellular biochemical signals to regulate cellular responses and tissue remodeling. Literature studies have confirmed that YAP/TAZ plays an important role not only in embryonic development, homeostasis and tumorigenesis, but also in mechanical-biochemical signal transduction of periodontal tissues under the mediation of various signal molecules in its upstream and downstream. Herein, we review the advances in the roles and mechanisms of YAP/TAZ in OTM to provide insights for better understanding and further study of the OTM and possible targeted clinical intervention in orthodontic treatment.

IGF1R controls mechanosignaling in myofibroblasts required for pulmonary alveologenesis

Ventilation throughout life is dependent on the formation of pulmonary alveoli, which create an extensive surface area in which the close apposition of respiratory epithelium and endothelial cells of the pulmonary microvascular enables efficient gas exchange. Morphogenesis of the alveoli initiates at late gestation in humans and the early postnatal period in the mouse. Alveolar septation is directed by complex signaling interactions among multiple cell types. Here, we demonstrate that IGF1 receptor gene (Igf1r) expression by a subset of pulmonary fibroblasts is required for normal alveologenesis in mice. Postnatal deletion of Igf1r caused alveolar simplification, disrupting alveolar elastin networks and extracellular matrix without altering myofibroblast differentiation or proliferation. Moreover, loss of Igf1r impaired contractile properties of lung myofibroblasts and inhibited myosin light chain (MLC) phosphorylation and mechanotransductive nuclear YAP activity. Activation of p-AKT, p-MLC, and nuclear YAP in myofibroblasts was dependent on Igf1r. Pharmacologic activation of AKT enhanced MLC phosphorylation, increased YAP activation, and ameliorated alveolar simplification in vivo. IGF1R controls mechanosignaling in myofibroblasts required for lung alveologenesis.

Regulation of endoplasmic reticulum stress and trophectoderm lineage specification by the mevalonate pathway in the mouse preimplantation embryo

Early embryos are vulnerable to environmental insults, such as medications taken by the mother. Due to increasing prevalence of hypercholesterolemia, more women of childbearing potential are taking cholesterol-lowering medications called statins. Previously, we showed that inhibition of the mevalonate pathway by statins impaired mouse preimplantation development, by modulating HIPPO signaling, a key regulator for trophectoderm (TE) lineage specification. Here, we further evaluated molecular events that are altered by mevalonate pathway inhibition during the timeframe of morphogenesis and cell lineage specification. Whole transcriptome analysis revealed that statin treatment dysregulated gene expression underlying multiple processes, including cholesterol biosynthesis, HIPPO signaling, cell lineage specification and endoplasmic reticulum (ER) stress response. We explored mechanisms that link the mevalonate pathway to ER stress, because of its potential impact on embryonic health and development. Upregulation of ER stress-responsive genes was inhibited when statin-treated embryos were supplemented with the mevalonate pathway product, geranylgeranyl pyrophosphate (GGPP). Inhibition of geranylgeranylation was sufficient to upregulate ER stress-responsive genes. However, ER stress-responsive genes were not upregulated by inhibition of ras homolog family member A (RHOA), a geranylgeranylation target, although it interfered with TE specification and blastocyst cavity formation. In contrast, inhibition of Rac family small GTPase 1 (RAC1), another geranylgeranylation target, upregulated ER stress-responsive genes, while it did not impair TE specification or cavity formation. Thus, our study suggests that the mevalonate pathway regulates cellular homeostasis (ER stress repression) and differentiation (TE lineage specification) in preimplantation embryos through GGPP-dependent activation of two distinct small GTPases, RAC1 and RHOA, respectively. Translation of the findings to human embryos and clinical settings requires further investigations.

The Effect of Physical Cues of Biomaterial Scaffolds on Stem Cell Behavior

Stem cells have been sought as a promising cell source in the tissue engineering field due to their proliferative capacity as well as differentiation potential. Biomaterials have been utilized to facilitate the delivery of stem cells in order to improve their engraftment and long-term viability upon implantation. Biomaterials also have been developed as scaffolds to promote stem cell induced tissue regeneration. This review focuses on the latter where the biomaterial scaffold is designed to provide physical cues to stem cells in order to promote their behavior for tissue formation. Recent work that explores the effect of scaffold physical properties, topography, mechanical properties and electrical properties, is discussed. Although still being elucidated, the biological mechanisms, including cell shape, focal adhesion distribution, and nuclear shape, are presented. This review also discusses emerging areas and challenges in clinical translation.

Integration of mechanical and ECM microenvironment signals in the determination of cancer stem cell states

Purpose of review

Cancer stem cells (CSCs) are increasingly understood to play a central role in tumor progression. Growing evidence implicates tumor microenvironments as a source of signals that regulate or even impose CSC states on tumor cells. This review explores points of integration for microenvironment-derived signals that are thought to regulate CSCs in carcinomas.

Recent findings

CSC states are directly regulated by the mechanical properties and extra cellular matrix (ECM) composition of tumor microenvironments that promote CSC growth and survival, which may explain some modes of therapeutic resistance. CSCs sense mechanical forces and ECM composition through integrins and other cell surface receptors, which then activate a number of intracellular signaling pathways. The relevant signaling events are dynamic and context-dependent.

Summary

CSCs are thought to drive cancer metastases and therapeutic resistance. Cells that are in CSC states and more differentiated states appear to be reversible and conditional upon the components of the tumor microenvironment. Signals imposed by tumor microenvironment are of a combinatorial nature, ultimately representing the integration of multiple physical and chemical signals. Comprehensive understanding of the tumor microenvironment-imposed signaling that maintains cells in CSC states may guide future therapeutic interventions.

Yes-associated protein 1 translocation through actin cytoskeleton organization in trophectoderm cells

A mammalian embryo experiences the first cell segregation at the blastocyst stage, in which cells giving form to the embryo are sorted into two lineages; trophectoderm (TE) and inner cell mass (ICM). This first cell segregation process is governed by cell position-dependent Hippo signaling, which is a phosphorylation cascade determining whether Yes-associated protein 1 (YAP1), one of the key components of the Hippo signaling pathway, localizes within the nucleus or cytoplasm. YAP1 localization determines the transcriptional on/off switch of a key gene, Cdx2, required for TE differentiation. However, the control mechanisms involved in YAP1 nucleocytoplasmic shuttling post blastocyst formation remain unknown. This study focused on the mechanisms involved in YAP1 release from TE nuclei after blastocoel contraction in bovine blastocysts. The blastocysts contracted by blastocoel fluid aspiration showed that the YAP1 translocation from nucleus to cytoplasm in the TE cells was concomitant with the protruded actin cytoskeleton. This YAP1 release from TE nuclei in the contracted blastocysts was prevented by actin disruption and stabilization. In contrast, Y27632, which is a potent inhibitor of Rho-associated coiled-coil containing protein kinase 1/2 (ROCK) activity, was found to promote YAP1 nuclear localization in the TE cells of contracted blastocysts. Meanwhile, lambda protein phosphatase (LPP) treatment inducing protein dephosphorylation could not prevent YAP1 release from TE nuclei in the contracted blastocysts, indicating that YAP1 release from TE nuclei does not depend on the Hippo signaling pathway. These results suggested that blastocyst contraction causes YAP1 release from TE nuclei through actin cytoskeleton remodeling in a Hippo signaling-independent manner. Thus, the present study raised the possibility that YAP1 subcellular localization is controlled by actin cytoskeletal organization after the blastocyst formation. Our results demonstrate diverse regulatory mechanisms for YAP1 nucleocytoplasmic shuttling in TE cells.

The role of RHOA signaling in trophectoderm cell-fate decision in cattle

Mammalian blastocysts are composed of two distinct cell lineages, namely the inner cell mass (ICM) and trophectoderm (TE). TE cells that give rise to the embryonic placenta are marked by an exclusive expression of the key determinant transcription factor, CDX2. Although Hippo signaling pathway is known to be responsible for this TE-specific expression of CDX2, the upstream regulator of this pathway in mammalian embryos is still controversial. In the present study, the involvement of the small molecular G protein, RHOA, in TE cell-fate decision in cattle was investigated. Inhibition of RHOA by the specific inhibitor, C3 transferase (C3), severely impaired the blastocyst formation. Further, C3 treatment significantly decreased the number of blastomeres with nuclearized YAP1, the prominent effector of Hippo pathway. An artificial isolation of ICM cells from blastocysts followed by the continuing culture to regenerate TE cells was conducted and showed that TE re-emergence from the isolated ICM is governed by Hippo pathway and suppressed by C3 treatment like that observed in developing embryos. Finally, the long-term exposure to C3 suggests the presence of alternative regulators of CDX2 expression other than RHOA signaling because there were still CDX2-positive cells after C3 treatment. These results demonstrated that RHOA signaling plays a significant role in TE cell-fate decision by regulating Hippo pathway in cattle.

Specification of the First Mammalian Cell Lineages In Vivo and In Vitro

Our understanding of how the first mammalian cell lineages arise has been shaped largely by studies of the preimplantation mouse embryo. Painstaking work over many decades has begun to reveal how a single totipotent cell is transformed into a multilayered structure representing the foundations of the body plan. Here, we review how the first lineage decision is initiated by epigenetic regulation but consolidated by the integration of morphological features and transcription factor activity. The establishment of pluripotent and multipotent stem cell lines has enabled deeper analysis of molecular and epigenetic regulation of cell fate decisions. The capability to assemble these stem cells into artificial embryos is an exciting new avenue of research that offers a long-awaited window into cell fate specification in the human embryo. Together, these approaches are poised to profoundly increase our understanding of how the first lineage decisions are made during mammalian embryonic development.

In vitro fertilization and embryo transfer alter human placental function through trophoblasts in early pregnancy

The mechanism underlying the potential risk associated with in vitro fertilization and embryo transfer (IVF‑ET) has been previously investigated but remains to be fully elucidated. As the placenta is a critical organ that sustains and protects the fetus, this is an important area of research. The aim of the present study was to determine the difference in trophoblast cell function in the first trimester between naturally conceived pregnancies and pregnancies achieved via IVF‑ET therapy. A total of 20 placental villi in first trimester samples were obtained through fetal bud aspiration from patients undergoing IVF‑ET due to oviductal factors between January 2016 and August 2018. In addition, a further 20 placental villi were obtained from those who naturally conceived and had normal pregnancies but were undergoing artificial abortion; these patients were recruited as the controls. Reverse transcription‑quantitative (RT‑q)PCR and semi‑quantitative immunohistochemical methods were used to detect the mRNA and protein expression of α‑fetoprotein (AFP), vascular endothelial growth factor (VEGF), transferrin (TF), tubulin β1 class VI (TUBB1), metallothionein 1G (MT1G), BCL2, glial cells missing transcription factor 1 (GCM1), epidermal growth factor (EGF) receptor (EGFR), PTEN and leukocyte associated immunoglobulin like receptor 2 (LAIR2) in villi from both groups. Differentially expressed genes were analyzed using Search Tool for the Retrieval of Interacting Genes, and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis was conducted. The RT‑qPCR data revealed that the mRNA expression levels of AFP, VEGF and TF were significantly higher in the IVF‑ET group than in the control group (P<0.05), and those of TUBB1, MT1G, BCL2, GCM1, EGFR, PTEN and LAIR2 were significantly lower (P<0.05). These gene products were expressed in the placental villus tissues, either in the cytoplasm, or in the membrane of syncytiotrophoblast and cytotrophoblast cells. The immunohistochemistry results were in line with those observed using RT‑qPCR. KEGG pathway analysis indicated that the trophoblast cell function of the IVF‑ET group in the first trimester was different from naturally conceived pregnancies with regard to proliferation, invasion, apoptosis and vascular development. The IVF‑ET process may trigger adaptive placental responses, and these compensatory mechanisms could be a risk for certain diseases later in life.

Maternal factors regulating preimplantation development in mice

Mammalian embryogenesis depends on maternal factors accumulated in eggs prior to fertilization and on placental transfers later in gestation. In this review, we focus on initial events when the organism has insufficient newly synthesized embryonic factors to sustain development. These maternal factors regulate preimplantation embryogenesis both uniquely in pronuclear formation, genome reprogramming and cell fate determination and more universally in regulating cell division, transcription and RNA metabolism. Depletion, disruption or inappropriate persistence of maternal factors can result in developmental defects in early embryos. To better understand the origins of these maternal effects, we include oocyte maturation processes that are responsible for their production. We focus on recent publications and reference comprehensive reviews that include earlier scientific literature of early mouse development.

Hippo signalling during development

The Hippo signalling pathway and its transcriptional co-activator targets Yorkie/YAP/TAZ first came to attention because of their role in tissue growth control. Over the past 15 years, it has become clear that, like other developmental pathways (e.g. the Wnt, Hedgehog and TGFβ pathways), Hippo signalling is a 'jack of all trades' that is reiteratively used to mediate a range of cellular decision-making processes from proliferation, death and morphogenesis to cell fate determination. Here, and in the accompanying poster, we briefly outline the core pathway and its regulation, and describe the breadth of its roles in animal development.

TEAD4, YAP1 and WWTR1 prevent the premature onset of pluripotency prior to the 16-cell stage

In mice, pluripotent cells are thought to derive from cells buried inside the embryo around the 16-cell stage. Sox2 is the only pluripotency gene known to be expressed specifically within inside cells at this stage. To understand how pluripotency is established, we therefore investigated the mechanisms regulating the initial activation of Sox2 expression. Surprisingly, Sox2 expression initiated normally in the absence of both Nanog and Oct4 (Pou5f1), highlighting differences between embryo and stem cell models of pluripotency. However, we observed precocious ectopic expression of Sox2 prior to the 16-cell stage in the absence of Yap1, Wwtr1 and Tead4. Interestingly, the repression of premature Sox2 expression was sensitive to LATS kinase activity, even though LATS proteins normally do not limit activity of TEAD4, YAP1 and WWTR1 during these early stages. Finally, we present evidence for direct transcriptional repression of Sox2 by YAP1, WWTR1 and TEAD4. Taken together, our observations reveal that, while embryos are initially competent to express Sox2 as early as the four-cell stage, transcriptional repression prevents the premature expression of Sox2, thereby restricting the pluripotency program to the stage when inside cells are first created.

Highlighted Article: The pluripotency marker SOX2 is not initially regulated by OCT4 and NANOG, but by HIPPO pathway members during the first 2 days of mouse embryogenesis.

AMOT130/YAP pathway in topography-induced BMSC osteoblastic differentiation

Micro/nano-topography (MNT) is an important variable affecting osseointegration of bone biomaterials, but the underlying mechanisms are not fully understood. We probed the role of a AMOT130/YAP pathway in osteoblastic differentiation of bone marrow mesenchymal stems cultured on titanium (Ti) carrying MNTs. Ti surfaces with two well-defined MNTs (TiO2 nanotubes of different diameters and wall thicknesses) were prepared by anodization. Rat BMSCs were cultured on flat Ti and Ti surfaces carrying MNTs, and cell behaviors (i.e., morphology, F-actin development, osteoblastic differentiation, YAP localization) were studied. Ti surfaces carrying MNTs increased F-actin formation, osteoblastic gene expression, and protein AMOT130 production in BMSCs (all vs. flat Ti), and the surface carrying larger nantubes was more effective, confirming osteoblastic differentiation induced by MNTs. Elevation of the AMOT130 level (by inhibiting its degradation) increased the osteoblastic gene expression, F-actin formation, and nuclear localization of YAP. These show that, AMOT130/YAP is an important pathway mediating the translation of MNT signals to BMSC osteoblastic commitment, likely via the cascade: AMOT130 promotion of F-actin formation, increased YAP nuclear import, and activation of osteoblastic gene expression.

RHOA activity in expanding blastocysts is essential to regulate HIPPO-YAP signaling and to maintain the trophectoderm-specific gene expression program in a ROCK/actin filament-independent manner

STUDY QUESTION

What molecular signals are required to maintain the functional trophectoderm (TE) during blastocyst expansion of the late stage of preimplantation development?

SUMMARY ANSWER

The activity of ras homology family member A (RHOA) GTPases is necessary to retain the expanded blastocyst cavity and also to sustain the gene expression program specific to TE.

WHAT IS KNOWN ALREADY

At the early stages of preimplantation development, the precursor of the TE lineage is generated through the molecular signals that integrate RHOA, RHO-associated coiled-coil containing protein kinase (ROCK), the apicobasal cell polarity, and the HIPPO-Yes-associated protein (YAP) signaling pathway. By contrast, molecular mechanisms regulating the maintenance of the TE characteristics at the later stage, which is crucial for blastocyst hatching and implantation, are scarcely understood.

STUDY DESIGN, SIZE, DURATION

Expanding mouse blastocysts, obtained from crosses of the F1 (C57BL6 × DBA/2) strain, were exposed to chemical agents that interfere with RHOA, ROCK, or the actin cytoskeleton for up to 8 h, and effects on the blastocyst cavity, HIPPO-YAP signaling, and cell lineage-specific gene expression profiles were examined.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Mouse embryos at the embryonic stage E3.5 (expanding blastocysts) and E4.5 (fully expanded blastocysts) were treated with RHOA inhibitor (C3 exoenzyme), ROCK inhibitor (Y27632), or actin filament disruptors (cytochalasin B and latrunculin A). The integrity of the blastocyst cavity was evaluated based on the gross morphology. Effects on HIPPO-YAP signaling were assessed based on the presence of nuclearized YAP protein by immunofluorescence staining and the expression of YAP/TEA domain family member (TEAD) target genes by quantitative RT-PCR (qRT-PCR). The impact of these disruptors on cell lineages was evaluated based on expression of the TE-specific and inner cell mass-specific marker genes by qRT-PCR. The integrity of the apicobasal cell polarity was assessed by localization of protein kinase C zeta (PRKCZ; apical) and scribbled planar cell polarity (SCRIB; basal) proteins by immunofluorescence staining. For comparisons, cultured cell lines, NIH/3T3 (mouse fibroblast) and P19C5 (mouse embryonal carcinoma), were also treated with RHOA inhibitor, ROCK inhibitor, and actin filament disruptors for up to 8 h, and effects on HIPPO-YAP signaling were assessed based on expression of YAP/TEAD target genes by qRT-PCR. Each experiment was repeated using three independent batches of embryos (n = 40-80 per batch) or cell collections. Statistical analyses of data were performed, using one-way ANOVA and two-sample t-test.

MAIN RESULTS AND THE ROLE OF CHANCE

Inhibition of RHOA deflated the cavity, diminished nuclear YAP (P < 0.01), and down-regulated the YAP/TEAD target and TE-specific marker genes in both E3.5 and E4.5 blastocysts (P < 0.05), indicating that the maintenance of the key TE characteristics is dependent on RHOA activity. However, inhibition of ROCK or disruption of actin filament only deflated the blastocyst cavity, but did not alter HIPPO-YAP signaling or lineage-specific gene expressions, suggesting that the action of RHOA to sustain the TE-specific gene expression program is not mediated by ROCK or the actomyosin cytoskeleton. By contrast, ROCK inhibitor and actin filament disruptors diminished YAP/TEAD target gene expressions in cultured cells to a greater extent than RHOA inhibitor, implicating that the regulation of HIPPO-YAP signaling in expanding blastocysts is distinctly different from that in the cell lines. Furthermore, the apicobasal cell polarity proteins in the expanding blastocyst were mislocalized by ROCK inhibition but not by RHOA inhibition, indicating that cell polarity is not linked to regulation of HIPPO-YAP signaling. Taken together, our study suggests that RHOA activity is essential to maintain the TE lineage in the expanding blastocyst and it regulates HIPPO-YAP signaling and the lineage-specific gene expression program through mechanisms that are independent of ROCK or actomyosin cytoskeleton.

LARGE-SCALE DATA

Not applicable.

LIMITATIONS, REASONS FOR CAUTION

This study was conducted using one species, the mouse. Direct translation of the experiments and findings to human fertility preservation and ART requires further investigations.

WIDER IMPLICATIONS OF THE FINDINGS

The elucidation of the mechanisms of TE formation is highly pertinent to fertility preservation in women. Our findings may raise awareness among providers of ART that the TE is sensitive to disturbance even in the late stage of blastocyst expansion and that rational approaches should be devised to avoid conditions that may impair the TE and its function.

STUDY FUNDING/COMPETING INTEREST(S)

This study was funded by grants from the Ingeborg v.F. McKee Fund of the Hawaii Community Foundation (16ADVC-78882 to V.B.A.), and the National Institutes of Health (P20 GM103457 and R03 HD088839 to V.B.A.). The authors have no conflict of interest to declare.

HIPPO signaling resolves embryonic cell fate conflicts during establishment of pluripotency in vivo

During mammalian development, the challenge for the embryo is to override intrinsic cellular plasticity to drive cells to distinct fates. Here, we unveil novel roles for the HIPPO signaling pathway in controlling cell positioning and expression of Sox2, the first marker of pluripotency in the mouse early embryo. We show that maternal and zygotic YAP1 and WWTR1 repress Sox2 while promoting expression of the trophectoderm gene Cdx2 in parallel. Yet, Sox2 is more sensitive than Cdx2 to Yap1/Wwtr1 dosage, leading cells to a state of conflicted cell fate when YAP1/WWTR1 activity is moderate. Remarkably, HIPPO signaling activity resolves conflicted cell fate by repositioning cells to the interior of the embryo, independent of its role in regulating Sox2 expression. Rather, HIPPO antagonizes apical localization of Par complex components PARD6B and aPKC. Thus, negative feedback between HIPPO and Par complex components ensure robust lineage segregation.

As an embryo develops, its cells divide, grow and migrate in specific patterns to build an organized collection of cells that go on to form our tissues and organs. One of the first steps – well before the embryo has implanted into the womb – is to allocate cells to make part of the placenta.

Once this process is complete, the remaining cells continue building the organism. These cells are pluripotent, meaning they can develop into any part of the body. Scientists think that the embryo manages to sort ‘placenta cells’ from pluripotent ones with the help of certain proteins, which the mother has packaged into her eggs.

To investigate this further, Frum et al. used genetic tools to track a specific gene called Sox2 that identifies pluripotent cells as soon as they are formed in mouse embryos. The experiments revealed that the mother places two closely related proteins known as YAP1 and WWTR1 within each egg, which help to make placenta cells different from pluripotent cells. Moreover, both proteins enable the embryo to segregate these two cell types to two different locations: placenta cells are moved to the outer layer of the embryo, while pluripotent cells are moved to the inside.

Current technologies allow researchers to create pluripotent cells in the laboratory. But these approaches often result in error, failing to replicate the embryo’s natural ability. By studying how embryos form and arrange pluripotent cells, scientists hope to advance stem cell technology (which emerge from pluripotent cells). This may help to find new ways to heal damaged tissues and organs, or to treat or even prevent many diseases.

AMOT130 linking F-actin to YAP is involved in intervertebral disc degeneration

OBJECTIVES

Dysregulation of YAP by the Hippo signalling is associated with intervertebral disc degeneration (IDD). However, the relationship between the F-actin and Hippo pathway in IDD, and their effects on YAP remain poorly understood.

METHODS

The characteristics of Hippo pathway and F-actin the in the NP (nucleus pulposus) and annulus fibrosus of immature, mature, ageing and disc degeneration model rats were observed by immunofluorescence, western blot and qPCR. Nucleus pulposus cells (NPCs) were transfected with lentivirus Sh-LATS A, Sh-LATS B and harvested for SA-β-gal staining, qPCR, western blotting and immunofluorescence staining to investigate the mechanism of Hippo pathway and F-actin interact in NPCs.

RESULTS

We observed moderate decreases in F-actin and YAP expression with age in healthy intervertebral discs (IVDs). F-actin stress fibres distributed throughout the cytoplasm disappeared following treatment with latrunculin B (Lat B), resulting in a punctate distribution. Depletion of large tumour suppressor homologues 1/2 (LATS1/2) did not decrease the rate of cellular senescence, and YAP remained in the cytoplasm following Lat B treatment. Furthermore, angiomotin 130 (AMOT130) was associated with F-actin through a conserved actin-binding domain to retain YAP in the cytoplasm.

CONCLUSIONS

This study showed that a mechanism by which Hippo pathway and F-actin synergize to modulate YAP activation and localization in the context of IDD and help to control NPCs proliferation.

E-cadherin in contact inhibition and cancer

E-cadherin is a key component of the adherens junctions that are integral in cell adhesion and maintaining epithelial phenotype of cells. Homophilic E-cadherin binding between cells is important in mediating contact inhibition of proliferation when cells reach confluence. Loss of E-cadherin expression results in loss of contact inhibition and is associated with increased cell motility and advanced stages of cancer. In this review we discuss the role of E-cadherin and its downstream signaling in regulation of contact inhibition and the development and progression of cancer.