Stimulation of Adult Muscle Stem Cells with BMPs Results in Direct Activation of Notch Pathway Genes.

Muscle stem cells (MuSCs) are the cellular source for the generation and regeneration of skeletal muscle. Proper muscle growth requires precise control over the differentiation and self-renewal of MuSCs. Signaling systems, such as bone morphogenetic proteins (BMPs) and Notch, suppress the myogenic differentiation of MuSCs. This allows the expansion of the progenitor pool necessary for muscle growth. To better understand the molecular mechanisms and target genes of BMPs during myogenesis, we examined the response of adult mouse MuSCs to BMP6. BMP6 stimulation of freshly isolated MuSCs suppressed myogenic differentiation. Short-term stimulation (one hour) rapidly increased the expression of classical BMP target genes, such as Id1, as well as Notch pathway genes, including Hes1, Hey1, Lfng, and Snai1. We used Cleavage Under Targets and Tagmentation (CUT&Tag) to generate whole-genome binding profiles for pSMAD1/5/9 and SMAD4, which are transcriptional effectors of the BMP pathway. This method detected dynamic binding in promoters and regulatory elements of direct BMP targets, including Notch pathway genes. Our data demonstrate that BMP6 is a potent suppressor of MuSC differentiation and reveal that a subset of well-characterized anti-myogenic genes (i.e., Hes1 and Hey1) are shared targets of the BMP and Notch pathways.