Apterous mediates development of direct flight muscles autonomously and indirect flight muscles through epidermal cues

Two physiologically distinct types of muscles, the direct and indirect flig ht muscles, develop from myoblasts associated with the Drosophila wing disc . We show that the direct flight muscles are specified by the expression of Apterous, a Lim homeodomain protein, in groups of myoblasts, This suggests a mechanism of cell-fate specification by labelling groups of fusion compe tent myoblasts, in contrast to mechanisms in the embryo, where muscle cell fate is specified by single founder myoblasts, In addition, Apterous is exp ressed in the developing adult epidermal muscle attachment sites. Here, it functions to regulate the expression of stripe, a gene that is an important element of early patterning of muscle fibres, from the epidermis, Our resu lts, which may have broad implications, suggest novel mechanisms of muscle patterning in the adult, in contrast to embryonic myogenesis.