Analyses of PS integrin functions during Drosophila development.

The Drosophila position-specific (PS) antigens are homologues of the vertebrate integrins, a family of transmembrane proteins that function in cell-matrix and cell-cell adhesion. The common beta subunit of PS integrins (PS beta) is encoded by the lethal(l)myospheroid gene (mys) and is required during wing, eye and muscle development. By expressing PS beta protein at defined developmental periods, we have shown that PS integrins are required throughout pupation, but not earlier, for normal development of wings. In contrast, the key requirement for PS integrins in eye development occurs only in the late pupa. Furthermore, PS integrins are apparently not required for the differentiation of the ommatidial cells; only for their organization. These results are consistent with roles for PS integrins in the interactions between the wing epithelia during the two phases of pupal wing expansion and in maintaining the attachment of a fully formed fenestrated membrane to the basement membrane of the retina. We have also examined the functional significance of alternative splicing of the transcript of the mys gene using P element-mediated transformation to introduce transgenes producing only one of the two spliced forms of PS beta. We find that either form is sufficient to rescue postembryonic mys phenotypes in the wing, eye and muscle but that both of the two splice forms are necessary to rescue the mys embryonic defects. This result indicates a requirement for the alternative splicing of mys during embryogenesis. The location of the alternative exons suggests that the two forms of the PS beta integrin subunit may interact with alternative alpha subunits and/or ligands.