Analysis of downstream effects of endogenous WNT signaling during cardiac differentiation of human ES cells
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ABSTRACT: WNT signaling inhibition at an intermediate stage of differentiation is a key requirement for cardiac induction of human ES cells, suggesting that endogenous WNT activity interferes with cardiomyocyte formation. Two downstream genes of endogenous WNT signaling, MSX1 and CDX2, were induced during cardiac differentiation to reveal whether they may account for the global negative effects played by endogenous WNT signaling in this process.
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:The homeoprotein Msx1 and Msx2 involved in normal skeletal muscle development and also contribute to muscle defects if altered during development. Deciphering the downstream signaling networks of Msx1 and Msx2 in myoblasts differentiation will help us to understand the molecular events that contribute to muscle defects. The objective of this study was to evaluate the proteomics characteristics in Msx1 and Msx2 mediated myoblasts differentiation, using isobaric tags for the relative and absolute quantification labelling technique (iTRAQ). The results showed that 1535 proteins with quantitative information were obtained. Volcano plots illustrated, in undifferentiated stage, 32 common downstream regulatory proteins for Msx1 and Msx2, 39 specific regulatory proteins for Msx1, and 13 specific for Msx2. While, in differentiated stage, 17 common downstream regulatory proteins for Msx1 and Msx2, 10 specific regulatory proteins for Msx1, and 21 specific for Msx2. Gene ontology, KEGG pathway and protein-protein interaction networks analyses revealed these proteins primarily associated with Arginine and proline metabolism, Glycolysis/Gluconeogenesis, Fatty acid degradation, Metabolism of xenobiotics by cytochrome P450 and Apoptosis. In addition, our data shows Acta1 was probably a core of the downstream regulatory networks of Msx1 and Msx2 in skeletal muscle development. The findings will help us to understand the molecular roles of Msx1 and Msx2 during muscle development as well as regeneration, and to understand the molecular events that contribute to muscle defects.
Project description:Neuroblastoma is an embryonal tumour of the peripheral sympathetic nervous system (SNS). One of the master regulator genes for peripheral SNS differentiation, the homeobox transcription factor PHOX2B, is mutated in familiar and sporadic neuroblastomas. Here we report that inducible expression of PHOX2B in the neuroblastoma cell line SJNB-8 down-regulates MSX1, a homeobox gene important for embryonic neural crest development. Inducible expression of MSX1 in SJNB-8 caused inhibition of both cell proliferation and colony formation in soft agar. Affymetrix micro- array and Northern blot analysis demonstrated that MSX1 strongly up-regulated the Delta-Notch pathway. These experiments describe for the first time regulation of the Delta-Notch pathway by MSX1, and connect these genes to the PHOX2B oncogene, indicative of a role in neuroblastoma biology. Keywords: Delta, Notch, MSX1, neuroblastoma, PHOX2B
Project description:Cardiac differentiation involves a stepwise clearance of repressors and fate-restricting regulators through the modulation of BMP/Wnt-signaling pathways. However, the mechanisms and how regulatory roadblocks are removed with specific developmental signaling pathways remain unclear. Here, we performed a genome-wide CRISPR screen to uncover essential regulators of cardiomyocyte specification in human embryonic stem cells (hESCs) and identify NF2, a Moesin-Ezrin-Radixin Like (MERLIN) Tumor Suppressor, as an upstream driver of cardiomyocyte specification. Transcriptional regulation and trajectory inference from NF2-null cells reveal the loss of cardiomyocyte identity and the acquisition of non-mesodermal identity. Sustained elevation of early mesoderm lineage repressor SOX2 and upregulation of late anti-cardiac regulators CDX2, MSX1 in NF2 knockout cells reflect a necessary role for NF2 in removing regulatory roadblocks. Since YAP is a known repressor of mesendoderm genes, we found that NF2 and AMOT cooperatively bind to YAP during mesendoderm formation, thereby preventing YAP activation independent on canonical MST-LATS1 kinase activity. Mechanistically, cardiomyocyte lineage identity was rescued by wild-type and NF2 Serine-518 phospho-mutants, but not NF2 FERM-domain blue-box mutants, showing that the critical FERM domain-dependent formation of the AMOT-NF2-YAP scaffold complex at the adherens junction is required for cardiomyocyte lineage differentiation. These results provide mechanistic insight into the essential role of NF2 for cardiomyocyte lineage specification by sequestering the repressive effect of YAP and relieving regulatory roadblocks en route to cardiomyocytes.
Project description:Mutations in MSX1 cause craniofacial developmental defects, including tooth agenesis, in humans and mice. Previous studies suggest that Msx1 activates Bmp4 expression in the developing tooth mesenchyme to drive early tooth organogenesis. Whereas Msx1−/− mice exhibit developmental arrest of all tooth germs at the bud stage, however, mice with neural crest-specific inactivation of Bmp4 (Bmp4ncko/ncko), which lack Bmp4 expression in the developing tooth mesenchyme, showed developmental arrest of only mandibular molars. We recently demonstrated that deletion of Osr2, which encodes a zinc finger transcription factor expressed in a lingual-to-buccal gradient in the developing tooth bud mesenchyme, rescued molar tooth morphogenesis in both Msx1−/− and Bmp4ncko/ncko mice. In this study, through RNA-seq analyses of the developing tooth mesenchyme in mutant and wildtype embryos, we found that Msx1 and Osr2 have opposite effects on expression of several secreted Wnt antagonists in the tooth bud mesenchyme. Remarkably, both Dkk2 and Sfrp2 exhibit Osr2-dependent preferential expression on the lingual side of the tooth bud mesenchyme and expression of both genes was up-regulated and expanded into the tooth bud mesenchyme in Msx1−/− and Bmp4ncko/ncko mutant embryos. We show that pharmacological activation of canonical Wnt signaling by either lithium chloride (LiCl) treatment or by inhibition of Dkk in utero was sufficient to rescue mandibular molar tooth morphogenesis in Bmp4ncko/ncko mice. Furthermore, whereas inhibition of Dkk alone was insufficient to rescue tooth morphogenesis in Msx1−/− mice, pharmacological inhibition of Dkk in combination with genetic inactivation of Sfrp2 and Sfrp3 rescued maxillary molar morphogenesis in Msx1−/− mice. Together, these data reveal a novel mechanism that the Bmp4-Msx1 pathway drives tooth organogenesis by activating Wnt signaling via regulation of the secreted Wnt antagonists.
Project description:Mutations in MSX1 cause craniofacial developmental defects, including tooth agenesis, in humans and mice. Previous studies suggest that Msx1 activates Bmp4 expression in the developing tooth mesenchyme to drive early tooth organogenesis. Whereas Msx1−/− mice exhibit developmental arrest of all tooth germs at the bud stage, however, mice with neural crest-specific inactivation of Bmp4 (Bmp4ncko/ncko), which lack Bmp4 expression in the developing tooth mesenchyme, showed developmental arrest of only mandibular molars. We recently demonstrated that deletion of Osr2, which encodes a zinc finger transcription factor expressed in a lingual-to-buccal gradient in the developing tooth bud mesenchyme, rescued molar tooth morphogenesis in both Msx1−/− and Bmp4ncko/ncko mice. In this study, through RNA-seq analyses of the developing tooth mesenchyme in mutant and wildtype embryos, we found that Msx1 and Osr2 have opposite effects on expression of several secreted Wnt antagonists in the tooth bud mesenchyme. Remarkably, both Dkk2 and Sfrp2 exhibit Osr2-dependent preferential expression on the lingual side of the tooth bud mesenchyme and expression of both genes was up-regulated and expanded into the tooth bud mesenchyme in Msx1−/− and Bmp4ncko/ncko mutant embryos. We show that pharmacological activation of canonical Wnt signaling by either lithium chloride (LiCl) treatment or by inhibition of Dkk in utero was sufficient to rescue mandibular molar tooth morphogenesis in Bmp4ncko/ncko mice. Furthermore, whereas inhibition of Dkk alone was insufficient to rescue tooth morphogenesis in Msx1−/− mice, pharmacological inhibition of Dkk in combination with genetic inactivation of Sfrp2 and Sfrp3 rescued maxillary molar morphogenesis in Msx1−/− mice. Together, these data reveal a novel mechanism that the Bmp4-Msx1 pathway drives tooth organogenesis by activating Wnt signaling via regulation of the secreted Wnt antagonists.
Project description:The first step in the development of human colorectal cancer (CRC) is the aberrant hyperactivation of the Wnt signaling pathway, predominantly caused by inactivating mutations in the adenomatous polyposis coli (APC) gene encoding an essential tumor suppressor. In order to identify genes affected by Apc loss, expression profiling of intestinal epithelium isolated from mice harboring the conditional allele of the gene was performed. The gene encoding transcriptional factor msh homeobox 1 (Msx1) displayed robust upregulation upon Apc inactivation. Subsequently, the expression pattern of human MSX1 was examined in a collection of colonic tumors. The MSX1 mRNA level was increased in all types of human intestinal neoplasia tested. In order to identify genes affected by MSX1 loss, expression profiling of human colorectal cancer cells SW620 upon MSX1 gene depletion was performed.
Project description:Surprisingly few pathways signal between cells, raising questions about mechanisms for tissue-specific responses. In particular, Wnt ligands signal in many mammalian tissues, including the intestinal epithelium, where constitutive signaling causes cancer. Genome-wide analysis of DNA cis-regulatory regions bound by the intestine-restricted transcription factor CDX2 in colonic cells uncovered highly significant over-representation of sequences that bind TCF4, a transcriptional effector of intestinal Wnt signaling. Chromatin immunoprecipitation confirmed TCF4 occupancy at most such sites and co-occupancy of CDX2 and TCF4 across short distances. A region spanning the single nucleotide polymorphism rs6983267, which lies within a MYC enhancer and confers colorectal cancer risk in humans, represented one of many co-occupied sites. Co-occupancy correlated with intestine-specific gene expression and CDX2 loss reduced TCF4 binding.These results implicate CDX2 in directing TCF4 binding in intestinal cells. Co-occupancy of regulatory regions by signal-effector and tissue-restricted transcription factors may represent a general mechanism for ubiquitous signaling pathways to achieve tissue-specific outcomes. A series of ChIP-chip experiments identified the CDX2 cistrome and discovered and validated extensive co-binding with TCF4 in colon cancer cell lines Transcriptional profiling following shRNA-mediated CDX2 knockdown was employed to identify CDX2-dependent gene expression in the human colon cancer cell line Caco2
Project description:Background Wnt signaling is implicated in many developmental decisions, including stem cell control, as well as in cancer. There are relatively few target genes known of the Wnt pathway. Results We have identified target genes of Wnt signaling using microarray technology and human embryonal carcinoma cells stimulated with active Wnt protein. The ~50 genes upregulated early after Wnt addition include the previously known Wnt targets Cyclin D1, MYC, ID2 and beta TRCP. The newly identified targets, which include MSX1, MSX2, Nucleophosmin, Follistatin, TLE/Groucho, Ubc4/5E2, CBP/P300, Frizzled and REST/NRSF, have important implications for understanding the roles of Wnts in development and cancer. The protein synthesis inhibitor cycloheximide blocks induction by Wnt, consistent with a requirement for newly synthesized beta - catenin protein prior to target gene activation. The promoters of nearly all the target genes we identified have putative TCF binding sites; and we show that the TCF binding site is required for induction of Follistatin. Several of the target genes have a cooperative response to a combination of Wnt and BMP. Conclusion Wnt signaling activates genes that promote stem cell fate and inhibit cellular differentiation; and regulates a remarkable number of genes involved in its own signaling system.