All known mbc alleles are recessive and cause fatal embryonic defects.
Mutant embryos lie motionless in the vitelline membrane and fail to hatch.
Mbc is one of the first proteins in Drosophila to be identified as being essential for myoblast fusion. It is expressed in a broad range of tissues throughout embryonic development, including the presumptive musculature and epidermal cells involved in the process of dorsal closure . Consistent with its expression pattern, mbc mutant embryos exhibit defects in dorsal closure and cytoskeletal organization as well as myoblast fusion. Mbc has striking homology to DOCK180, a human gene that was identified on the basis of its interaction with the small adapter protein Crk. Because mbc is expressed early in the ectoderm and persists in the epidermis, mbc mutant embryos were examined for epidermal defects.