The lethal myospheroid gene of Drosophila encodes a membrane protein homologous to vertebrate integrin beta subunits.

A mutant of Drosophila melanogaster carrying the lethal(1) myospheroid mutation [l(1)mys] has a defective musculature and a phenotype that suggests a defect of basement membranes. The genomic region that is interrupted by an insertion in a mutant carrying l(1)mys was used to isolate cDNA clones, and their sequences are presented here. The cDNA sequence predicts a cysteine-rich integral membrane protein that displays 45% sequence identity to chicken integrin and the human fibronectin receptor beta subunit and much greater similarity over localized segments. These similarities extend to other vertebrate integrin beta subunits, and we conclude that the myospheroid protein is an integrin beta subunit of Drosophila. This implies evolutionary conservation of a group of transmembrane proteins that are receptors for extracellular matrix and, coupled with the myospheroid phenotype, indicates an important role for the interaction of cells with extracellular matrix during development.