DEVELOPMENT OF THE INDIRECT FLIGHT-MUSCLE ATTACHMENT SITES IN DROSOPHILA - ROLE OF THE PS INTEGRINS AND THE STRIPE GENE

Using markers that are expressed at muscle attachment sites, we have e xamined the early pupal development (first 36 hr) of Indirect Flight M uscle (IFM) attachments in the fruit fly Drosophila melanogaster. Expr ession of the Drosophila homologs of vertebrate integrins, the Positio n-Specific (PS) antigens, is known to differentially mark epidermal (P S1 alpha) and muscle (PS2 alpha) components of the developing IFM atta chment sites. During myogenesis, PS2 alpha is detected transiently in imaginal myoblasts that fuse with persistent larval muscles to give ri se to the Dorsal Longitudinal Muscles (DLMs), but not in myoblasts tha t fuse de novo to give rise to the Dorso Ventral Muscles. The integrin s are not expressed at attachment sites when the muscle fibers first m ake their appearance (12-20 hr). following muscle-epidermal contact, P S1 and PS2 are detected at muscle attachment sites. PS1 expression is at the muscle ends and also in the long epidermal processes that conne ct the developing muscle fibers to their sites of attachment in the ep idermis, while PS2 expression is restricted to the muscle ends. Epider mal cells that will contribute to the adult attachment sites are defin ed as early as the third larval instar. Both anterior and posterior si tes of attachment of the IFMs are marked by the expression of reporter beta-galactosidase activity in a P-element line B14.0, which is an in sertion at the stripe locus. B14.0 (stripe) is seen in distinct domain s in the wing and leg imaginal discs which give rise to the thoracic c uticle. The expression is maintained during pupal development. The B14 .0 (stripe) expressing epidermal cells contact the developing muscle f ibers, leading to the formation of the myotendon junction. We show tha t the dorsal and ventral attachment sites of one group of IFMs, the DV Ms arise from two different imaginal discs (wing and leg, respectively ), which may explain the differential effect of mutations such as bend less on these muscles. Attachment sites for the other group of IFMs, t he DLMs, on the other hand, arise from one imaginal disc (wing). B14.0 (stripe) expression defines epidermal cells of the adult attachment s ites and is likely to function during early events leading to the form ation of muscle-epithelial contacts. The PS integrins are detected at later stages, suggesting a role in the stabilization and maturation of the muscle-epidermal contacts into myotendon junctions. (C) 1996 Acad emic Press, Inc.