BMP4 triggers regulatory circuits specifying the cardiac mesoderm lineage

Abstract

Cardiac lineage specification in the mouse is controlled by TGFβ and WNT signaling. From fly to fish, BMP has been identified as indispensable heart inducer. A detailed analysis of the role of Bmp4 and its effectors Smad1/5, however, were still missing. We show that Bmp4 induces cardiac mesoderm formation in murine ESCs in vitro. Bmp4 first activates Wnt3 and up-regulates 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.

Early neural specification of stem cells is mediated by a set of SOX2-dependent neural-associated enhancers

“…During development, SOX2 antagonizes and inhibits expression of the ME TFs Eomes and T ( Koch et al., 2017 ; Blassberg et al., 2022 ; Wang et al., 2012 ; Thomson et al., 2011 ). We recently showed that ME TFs induce differentiation by activating ME enhancers via increasing their accessibility ( Tsaytler et al., 2023 ). We hypothesized that opening of DARs in SOX2 KO cells may be mediated by ME TFs and analyzed the binding of pSMAD1/5, pSMAD2, EOMES, and T to these DARs in ME cells ( Figures S1 D and S1E).…”

“…We have recently shown that during BMP4-induced ME differentiation, Sox2 is repressed by mesodermal TFs, and neural fate genes are not expressed during the differentiation course ( Tsaytler et al., 2023 ). At early stages of WT ESC differentiation, Sox2 repression is mediated by SMAD4, whereas loss of Smad4 results in rapid up-regulation of neural fate genes in BMP4-treated cells despite the absence of NE inducers ( Tsaytler et al., 2023 ). Here, we showed that SOX2 ablation in ESCs leads to opening of enhancers bound by ME TFs ( Figures S1 D–S1F).…”

“…RNA extraction and library preparation were performed as previously described ( Koch et al., 2017 ; Tsaytler et al., 2023 ).…”

State-of-the-Art Differentiation Protocols for Patient-Derived Cardiac Pacemaker Cells

“…These directly activate the primary cardiac mesoderm regulator, mesoderm posterior BHLH transcription factor 1 (Mesp1) [ 20 , 21 ], and the family member Mesp2 [ 22 ]. This mechanism is reinforced by the activation of TGF-β superfamily signaling by Nodal and BMP4 (bone morphogenetic protein 4) agonists [ 23 , 24 ]. Together with Mesp1/2, Nodal and BMP4 induce the expression of the platelet-derived growth factor receptor-α (Pdgfr-α), which can be used to effectively monitor the emergence of cardiovascular mesoderm [ 25 ].…”

“…DKK1, which subsequently inhibits Wnt/β-catenin signaling, converts the anterior mesoderm into a cardiogenic mesoderm ( Figure 1 ) [ 20 , 21 , 26 ]. Together with Wnt/β-catenin signaling inhibition, BMP4 and the fibroblast growth factor (FGF) support cardiac mesoderm formation [ 23 , 27 ]. In the posterior component, where Wnt/β-catenin signaling is still active and notochord (axial mesoderm)-released Noggin inhibits BMP4, the lateral plate mesoderm becomes the hemangiogenic mesoderm [ 28 , 29 ].…”