MODULAR REGULATION OF MUSCLE GENE-TRANSCRIPTION - A MECHANISM FOR MUSCLE-CELL DIVERSITY

Skeletal, cardiac and smooth muscle cells express overlapping sets of muscle-specific genes, such that some muscle genes are expressed in on ly a single muscle cell type, whereas others are expressed in multiple muscle cell lineages. Recent studies in transgenic mice have revealed that, in many cases, multiple , independent cis-regulatory regions, o r modules, are required to direct the complete development pattern of expression of individual muscle-specific genes, even within a single m uscle cell type. The temporospatial specificity of these myogenic regu latory modules is established by unique combinations of transcription factors and has revealed unanticipated diversity in the regulatory pro grams that control muscle gene expression. This type of composite regu lation of muscle gene expression appears to reflect a general strategy for the control of cell-specific gene expression.