THE PS2 INTEGRIN LIGAND TIGGRIN IS REQUIRED FOR PROPER MUSCLE FUNCTION IN DROSOPHILA

Tiggrin is a novel extracellular matrix ligand for the Drosophila PS2 integrins, We have used flanking P elements to generate a precise dele tion of tiggrin. Most flies lacking tiggrin die as larvae or pupae, A few adults do emerge and these appear to be relatively normal, display ing only misshapen abdomens and a low frequency of wing defects, Exami nation of larvae shows that muscle connections, function and morpholog y are defective in tiggrin mutants. Muscle contraction waves that exte nd the length of the larvae are much slower in tiggrin mutants, Direct examination of bodywall muscles shows defects in muscle attachment si tes, where tiggrin is specifically localized, and muscles appear thinn er. Transgenes expressing tiggrin are capable of rescuing tiggrin muta nt phenotypes, Transgenes expressing a mutant tiggrin, whose Arg-Gly-A sp (RGD) integrin recognition sequence has been mutated to Leu-Gly-Ala (LGA) show much reduced, but significant, rescuing ability. Cell spre ading assays detect no interactions of this mutant tiggrin with PS2 in tegrins, Therefore, while the RGD sequence is critical for PS2 interac tions and full activity in the whole fly, the mutant tiggrin retains s ome function(s) that are probably mediated by interactions with other ECM molecules or cell surface receptors.