GENETIC-ANALYSIS OF NETRIN GENES IN DROSOPHILA - NETRINS GUIDE CNS COMMISSURAL AXONS AND PERIPHERAL MOTOR AXONS

Two tandem Netrin genes in Drosophila are expressed at the midline of the developing CNS and in different subsets of neurons, muscles, and e pidermal patches. In embryos carrying a small deficiency that deletes both genes, CNS axon commissures are partially missing or thinner. Thi s phenotype is rescued by expressing either Netrin gene at the midline . Pan-neural expression of either gene causes disruption of commissura l and longitudinal tracts, indicating that the pattern of Netrin expre ssion is crucial and that Netrins function as instructive cues. The do uble mutant also shows defects in motor axon projections. Expression o f either Netrin gene in all muscles also results in aberrant motor pro jections. Thus, Drosophila Netrins are required for the guidance of co mmissural axons at the midline, and of motor axons to their target mus cles.