The function of PS integrins in Drosophila embryo and wing morphogenesis.

Abstract

The position-specific (PS) integrins of Drosophila are homologous in structure and function to vertebrate integrins, a family of transmembrane receptors that facilitate mechanical linkage and signal transduction between extracellular molecules and the cytoskeleton. Most integrins, including PS integrins, are receptors for components of the extracellular matrix. Integrins are αβ heterodimers, and structural domains within both subunits typically influence ligand specificity. PSI and PS2 integrins are composed of unique α subunits, α(PS1) or α(PS2), and share a common β subunit (β(ps)). myospheroid (mys) encodes β(ps), and the characterization of mys phenotypes indicates that PS integrins function during tissue morphogenesis; e.g., PS integrins are required for adhesion of embryonic muscles to their body wall attachments, and for adhesion between the two surfaces of the pupal wing blade. During metamorphosis, the flat bilayered adult wing blade is formed from a single layered larval wing disc, and removal of PS integrins from this process causes wing "blisters". Since wing morphogenesis is a lengthy and dynamic process, the temporal requirement for integrin function was unclear. Using heatshock inducible mys+ transgenes, the wing blister phenotype of animals with compromised integrin function was rescued. By varying the times of transgene induction, I find that integrin function is required from very early in metamorphosis until at least the last 24-48 hours of wing development. Since the inflated (if) gene encodes α(PS2), characterization of if phenotypes promised to reveal the developmental requirements specific for PS2. New if lethal alleles were generated and found to retain little or no wildtype UPS2 function. As seen for mys mutants, if mutant embryos show extreme defects in somatic muscle attachments and in midgut morphogenesis. Unlike mys, however, there is no dorsal herniation in if mutant embryos. With respect to wing morphogenesis, clonal analysis experiments demonstrate that if+ function is required only in cells of the ventral wing surface. To examine the in vivo functions of distinct integrin structures, transgenes were created to express either PS2 subtype, PS2m8 or PS2c. I find that PS2m8 or PS2c rescues the if- muscle phenotype. In contrast, ectopic PS2m8 (but not PS2c) activity dominantly disrupts wing morphogenesis.