NETRIN and SLIT guide salivary gland migration.

Directed migration is pivotal for the proper placement and function of nearly all organs. The majority of known guidance molecules involved in directed migration have been identified from studies of migrating axons during nervous system development. Here, we show that at least two of these axon guidance molecules, NETRIN and SLIT, act through their canonical receptors, to guide Drosophila embryonic salivary glands. NETRIN serves as a chemo-attractant while SLIT functions antagonistically to NETRIN as a chemo-repellent during salivary gland migration. CNS midline expression of both NETRIN and SLIT directs the glands to move unswervingly parallel to the CNS. NETRIN expression is also required in the visceral mesoderm, along which the glands move during their migration. We propose that analogous to axon guidance, a balance between chemo-attractants and chemo-repellents is required for the proper migratory path of the developing salivary glands.