Project description:In hESCs, Wnt3/β-catenin activity is low and Activin/SMAD signaling ensures NANOG expression to sustain pluripotency. In response to exogenous Wnt3 effectors, Activin/SMADs switch to cooperate with β-catenin and induce mesendodermal differentiation genes. We show here that the HIPPO effector YAP binds to the WNT3 gene enhancer and prevents the gene from being induced by Activin in proliferating hESCs. In the absence of YAP, Activin signaling is sufficient to induce expression of the endogenous Wnt3 cytokine, which stabilizes β-catenin and selectively activates genes required for cardiac mesoderm (ME) formation. Interestingly, Activin-stimulated YAP-knockout hESCs strongly express β-catenin-dependent cardiac mesoderm markers (BAF60c and HAND1), but unlike WT hESCs, fail to express cardiac inhibitor genes (CDX2, MSX1). Accordingly, YAP-/- cells treated with Activin alone can differentiate efficiently to beating cardiomyocytes in culture, bypassing the need for sequential treatment with exogenous Wnt ligand and Wnt inhibitors. Similarly, Activin in combination with small-molecule YAP inhibitors generates beating cardiomyocytes from wild-type hESCs following a one- step protocol. Our findings highlight an unanticipated role of YAP as an upstream regulator of WNT3 to maintain hESC pluripotency in the presence of Activin, and uncover a direct route for the development of human embryonic cardiac mesoderm.
Project description:A hESC MESP1-MCHERRY reporter line was used to isolate and study the molecular character of MESP1 expressing pre-cardiac progenitors, derived from hESC. MESP1 is a key-transcription factor for pre-cardiac mesoderm and is marking the progenitor for almost all cells of the heart. This reporter line was used to study cardiac differentiation and the derivation of early cardiac progenitors in vitro. hESCs were differentiated towards the cardiac lineage, expressing MESP1-mCherry at day 3 of differentiation. Total RNA obtained from isolated MESP1-mCherry expressing progenitors was compared to that of non-MESP1-expressing progenitors and undifferentiated hESCs in order to characterize MESP1-specific transcription factors and proteins.
Project description:YAP transcriptional regulator controls cell mechanics by activating genes involved in cell-matrix interaction following extracellular matrix (ECM) remodelling and stiffening. YAP is needed for cardiogenesis in mouse but is repressed in adult cardiomyocytes. The protein is reactivated following ischemic insults, although the timing and mechanisms underlying YAP depletion during heart development and the reason for its reactivation are unclear. Here, we combine pluripotent stem cell (PSC) cardiac differentiation, mouse embryo development and human heart tissue analysis to demonstrate that the fine-tuning of cell mechanics, as controlled by YAP multiphasic activation through TEAD transcription, is crucial for mesoderm commitment and cardiac progenitor specification. Finally, by adopting induced PSC models of dilated cardiomyopathy, we prove that YAP-TEAD reactivation in diseased cardiomyocytes empowers calcium handling apparatus and increases cell contractility. Given YAP prompt activation following myocardial infarction, we unveil a novel role for mechanosensing in connecting ECM remodelling to cardiomyocyte function in pathological heart.
Project description:YAP transcriptional regulator controls cell mechanics by activating genes involved in cell-matrix interaction following extracellular matrix (ECM) remodelling and stiffening. YAP is needed for cardiogenesis in mouse but is repressed in adult cardiomyocytes. The protein is reactivated following ischemic insults, although the timing and mechanisms underlying YAP depletion during heart development and the reason for its reactivation are unclear. Here, we combine pluripotent stem cell (PSC) cardiac differentiation, mouse embryo development and human heart tissue analysis to demonstrate that the fine-tuning of cell mechanics, as controlled by YAP multiphasic activation through TEAD transcription, is crucial for mesoderm commitment and cardiac progenitor specification. Finally, by adopting induced PSC models of dilated cardiomyopathy, we prove that YAP-TEAD reactivation in diseased cardiomyocytes empowers calcium handling apparatus and increases cell contractility. Given YAP prompt activation following myocardial infarction, we unveil a novel role for mechanosensing in connecting ECM remodelling to cardiomyocyte function in pathological heart.
Project description:Cardiac lineage specification in the mouse is controlled by TGFβ and WNT signaling. From fly to fish, BMP has been identified as an indispensable heart inducer. A detailed analysis of the role of Bmp4 and its effectors Smad1/5, however, was still missing. We show that Bmp4 induces cardiac mesoderm formation in murine embryonic stem cells in vitro. Bmp4 first activates Wnt3 and upregulates Nodal. pSmad1/5 and the WNT effector Tcf3 form a complex, and together with pSmad2/3 activate mesoderm enhancers and Eomes. They then cooperate with Eomes to consolidate the expression of many mesoderm factors, including T. Eomes and T form a positive feedback loop and open additional enhancers regulating early mesoderm genes, including the transcription factor Mesp1 establishing the cardiac mesoderm lineage. In parallel, the neural fate is suppressed. Our data confirm the pivotal role of Bmp4 in cardiac mesoderm formation in the mouse. We describe in detail the consecutive and cooperative actions of three signaling pathways, BMP, WNT and Nodal, and their effector transcription factors, during cardiac mesoderm specification.
Project description:TMEM88 is indispensable for heart development and acts in the pre-cardiac mesoderm to specify lineage commitment of the cardiovascular progenitor cell through inhibition of Wnt signaling. 2 different lentiviruses expression shRNA targeting different domains of the TMEM88 locus were transduced into undifferentiated hES cells. Cells were puromycin selected then differentiated along the cardiac lineage. Total RNA was taken at day 5 of differentiation when the cardiovascular progenitor cell arises. 1 sample for each shRNA and 2 samples for control shRNA were analyzed by array
Project description:Self-organisation and coordinated morphogenesis of multiple cardiac lineages is essential for the development and function of the heart1-3. However, the absence of a human in vitro model that mimics the basic lineage architecture of the heart hinders research into developmental mechanisms and congenital defects4. Here, we describe the establishment of a reliable, lineage-controlled and high-throughput cardiac organoid platform. We show that cardiac mesoderm derived from human pluripotent stem cells robustly self-organises and differentiates into cardiomyocytes forming a cavity. Co-differentiation of cardiomyocytes and endothelial cells from cardiac mesoderm within these structures is required to form a separate endothelial layer. As in vivo, the epicardium engulfs these cardiac organoids, migrates into the cardiomyocyte layer and differentiates. We use this model to demonstrate that cardiac cavity formation is controlled by a mesodermal WNT-BMP signalling axis. Disruption of one of the key BMP targets in cardiac mesoderm, the transcription factor HAND1, interferes with cavity formation, which is consistent with its role in early heart tube and left chamber development5. Thus, the cardiac organoid platform represents a powerful resource for the quantitative and mechanistic analysis of early human cardiogenesis and defects that are otherwise inaccessible. Beyond understanding congenital heart disease, cardiac organoids provide a foundation for future translational research into human cardiac disorders.
Project description:Single-cell RNA-seq reveals that Polycomb repressive complex 2 (PRC2) maintains naïve pluripotency and restricts an intrinsic capacity of pre-implantation pluripotent stem cells to give rise to trophectoderm and mesoderm lineages. Inhibition of PRC2 forces naïve hESC into an ‘activated’ state through which differentiation into either trophectoderm or mesoderm lineages is triggered. This trajectory is distinct from embryonic lineage specification out of the post-implantation pluripotent state, hence PRC2-mediated repression provides a highly adaptive mechanism to restrict lineage potential during early human development.
Project description:A hESC MESP1-MCHERRY reporter line was used to isolate and study the molecular character of MESP1 expressing pre-cardiac progenitors, derived from hESC. MESP1 is a key-transcription factor for pre-cardiac mesoderm and is marking the progenitor for almost all cells of the heart. This reporter line was used to study cardiac differentiation and the derivation of early cardiac progenitors in vitro.
Project description:Polycomb complexes are essential regulators of stem cell identity, yet very little is known about their molecular mechanisms during cell differentiation. Pcgf proteins (Pcgf1/2/3/4/5/6) are core subunits of the Polycomb repressive complex 1 (PRC1). It has been recently proposed that specific Pcgf proteins are associated to particular PRC1 complexes, yet the molecular and biological functions of different Pcgf proteins remains largely elusive. Using specific differentiation protocols, we have elucidated a role for Pcgf2/Mel18 in specifically regulating mesoderm differentiation. Mechanistically, during early cardiac mesoderm differentiation, Pcgf2/Mel18 functions as a classical Polycomb protein by repressing pluripotency, lineage specification, late cardiac differentiation and negative regulators of the BMP pathway, yet Pcgf2/Mel18 also positively regulates the expression of key mesoderm transcription factors, revealing a novel function of Pcgf2/Mel18 in gene activation during cardiac differentiation. Mel18 depletion results in an unbalance of pathways that positively and negatively regulate cardiac differentiation. We propose that Mel18 is a novel epigenetic factor that controls mesoderm differentiation by opposing molecular mechanisms. List of ChIPseq samples: Mel18 in ESCs and MES, Ring1b, RYBP and Cbx2 in MES, IgG in MESs. List of RNAseq experiments: Mel18 KD, Ring1b KO and CTR in ESCs, Mel18 KD and CTR in MES, Mel18 KD and CTR in CMs.