A distinct set of founders and fusion-competent myoblasts make visceral muscles in the Drosophila embryo

The embryonic Drosophila midgut is enclosed by a latticework of longitudina l and circular visceral muscles. We find that these muscles are syncytial. Like the somatic muscles they are generated by the prior segregation of two populations of cells: fusion-competent myoblasts and founder myoblasts spe cialised to seed the formation of particular muscles. Visceral muscle found ers are of two classes: those that seed circular muscles and those that see d longitudinal muscles. These specialisations are revealed in mutant embryo s where myoblast fusion fails. In the absence of fusion, founders make mono nucleate circular or longitudinal fibres, while their fusion-competent neig hbours remain undifferentiated.