Abstract: The present invention relates to promoters, enhancers and other regulatory elements that direct expression within SMC, comprising nucleotide sequences from the 5′ regulatory region and the first intron, and transcriptionally active fragments thereof, that control expression of an SM &agr;-A. Specifically provided are expression vectors, host cells and transgenic animals wherein an SM &agr;-A regulatory region is capable of controlling expression of a heterologous gene, over-expressing an endogenous SMC gene or an inhibitor of a pathological process or knocking out expression of a specific gene believed to be important for an SM-related disease in SMC. The invention also relates to methods for using said vectors, cells and animals for screening candidate molecules for agonists and antagonists of disorders involving SMC. The invention further relates to compositions and methods for modulating expression of compounds within SMC, and to screening compounds that modulate expression within SMC.