Regulation of Skeletal Myoblast Differentiation by Drebrin

Myoblast differentiation is a complex process. As myoblasts differentiate into myofibers, they acquire a cell type-specific transcriptional program, irreversibly exit the cell cycle, and dramatically change their morphology. The morphological changes include cell elongation, alignment, and fusion into syncytial myofibers. Several lines of evidence suggest that these events may be co-regulated. However, the mechanisms that coordinate major alterations in a cell's transcriptome and its shape are not well understood. Muscle-specific transcription is controlled by proteins of the MyoD family, transcription factors whose activity is regulated by specific signal transduction pathways, including the p38 MAP kinase pathway. In a search for genes that might play a role in linking myogenic signal transduction, cytoskeletal regulation, and myoblast differentiation, Dbn1 (encoding the actin regulator drebrin) was identified. Dbn1 expression is induced during myoblast differentiation, in a p38 MAP kinase- and MyoD- dependent manner. RNAi-mediated depletion of drebrin, or treatment with a chemical drebrin inhibitor, resulted in a similar phenotype in myoblasts: defective differentiation, with low levels of early and late differentiation markers and inefficient production of myofibers. Drebrin localizes at sites of cell-cell contact and cell extensions, locations that are also enriched for F-actin. Drebrin may be important in linking transcriptional and morphological aspects of myoblast differentiation.