Lethal of scute, a proneural gene, participates in the specification of muscle progenitors during Drosophila embryogenesis.

The mechanisms that underlie the segregation of muscle founder cells in the Drosophila embryo are undefined. We show that the proneural gene lethal of scute (l'sc) is expressed in clusters of cells in the somatic mesoderm, from which individual muscle progenitors are singled out by progressive restriction of l'sc expression. Coexpression of l'sc and S59 (a putative muscle identity gene) in a subset of muscle progenitors shows that muscle founders are produced by division of muscle progenitors. In neurogenic mutant embryos the restriction of l'sc expression fails and all cells in a cluster coexpress l'sc and S59. Loss-of-function and overexpression phenotypes indicate a role for l'sc in the segregation of muscle progenitors and the formation of the muscle pattern.