Genetic analysis on the role of integrin during axon guidance in Drosophila.

Heterodimeric cell surface receptor integrin is widely expressed in the nervous system, but its specific role during axon development has not been directly tested in vivo. We show that the Drosophila nervous system expresses low levels of positron-specific (PS) integrin subunits alphaPS1, alphaPS2, and betaPS during embryonic axogenesis. Furthermore, certain subsets of neurons express higher levels of integrin mRNAs than do the rest. Null mutations in either the alphaPS1 or alphaPS2 subunit gene cause widespread axon pathfinding errors that can be rescued by supplying the wild-type integrin subunit to the mutant nervous system. In contrast, misexpressing either the alphaPS1 or alphaPS2 integrin subunit in all neurons leads to no obvious axon pathfinding errors. We propose that integrin does not itself serve as either a "clutch" constituting molecule or a specific growth cone "receptor," as proposed previously, but rather as part of a molecular network that cooperatively guarantees accurate axon guidance.