The Beat generation: a multigene family encoding IgSF proteins related to the Beat axon guidance molecule in Drosophila

A previous genetic screen led to the identification of the beaten path (bea t Ia) gene in Drosophila. Beat Ia contains two immunoglobulin (Ig) domains and appears to function as an anti-adhesive factor secreted by specific gro wth cones to promote axon defasciculation. We identify a family of 14 beat- like genes in Drosophila. In contrast to beat Ia, four novel Beat-family ge nes encode membrane-bound proteins. Moreover, mutations in each gene lead t o much more subtle guidance phenotypes than observed in beat Ia. Genetic in teractions between beat Ic and beat Ia reveal complementary functions. Our data suggest a model whereby Beat Ic (and perhaps other membrane-bound fami ly members) functions in a pro-adhesive fashion to regulate fasciculation, while Beat Ia (the original secreted Beat) functions in an anti-adhesive fa shion to regulate defasciculation.