Embryonic axon guidance: insights from Drosophila and other insects.

During embryonic development, growing axons are guided by cellular signaling pathways that control a series of individual axon guidance decisions. In Drosophila, two major pathways (Netrin-Frazzled/DCC and Slit-Robo) regulate axon guidance in the embryonic ventral nerve cord, including the critical decision of whether or not to cross the midline. Studies in the fruit fly have revealed a complex picture of precise regulation and cross-talk between these pathways. In addition, Robo receptors in Drosophila have diversified their activities to regulate additional axon guidance decisions in the developing embryo. Here, I discuss recent advances in understanding roles and regulation of the Net-Fra and Slit-Robo signaling pathways in Drosophila, and examine the evolutionary conservation of these signaling mechanisms across insects and other arthropods.