The Mediator complex functions as a control center, orchestrating diverse signaling, gene activities, and biological processes.
However, how Mediator subunits determine distinct cell fates remains to be fully elucidated. Here, we show that Mediator MED23
controls the cell fate preference that directs differentiation into smooth muscle cells (SMCs) or adipocytes. Med23 deficiency facilitates SMC differentiation but represses adipocyte differentiation from the multipotent mesenchymal stem
cells. Gene profiling revealed that the presence or absence of Med23 oppositely regulates two sets of genes: the RhoA/MAL targeted cytoskeleton/SMC genes and the Ras/ELK1 targeted growth/adipogenic
genes. Mechanistically, MED23 favors ELK1–SRF binding to SMC gene promoters for repression, whereas the lack of MED23 favors
MAL–SRF binding to SMC gene promoters for activation. Remarkably, the effect of MED23 on SMC differentiation can be recapitulated
in zebrafish embryogenesis. Collectively, our data demonstrate the dual, opposing roles for MED23 in regulating the cytoskeleton/SMC
and growth/adipogenic gene programs, suggesting its “Ying-Yang” function in directing adipogenesis versus SMC differentiation.