The molecular mechanisms controlling smooth muscle differentiation are unknown. In an effort to elucidate these mechanisms, we examined the promoter region of a smooth muscle-specific gene, $\gamma$-smooth muscle isoactin. Our results demonstrate a role for serum response factor (SRF) in mediating the positive regulation of this gene. Because of the wide pattern expression of SRF, as well as its ability to complex with other transcription factors, it is likely that the SRF co-factors are responsible for the smooth muscle-specific expression of $\gamma$-smooth muscle isoactin. Additionally, we have preliminary evidence that BMP-4 and type IV collagen are able to promote intestinal smooth muscle cell (ISMC) differentiation. Furthermore, it appears that type IV collagen operates through a BMP-4-dependent manner. Together, this data significantly narrows the search for smooth muscle-specific transcription factors.
