A frazzled/DCC-dependent transcriptional switch regulates midline axon guidance

Stop-Go Axon Crossing Developing axons may or may not cross the body's midline according to a balance between repulsive and attractive guidance factors. As an axon first approaches the midline, a repressive receptor encoded by the comm gene is inactivated by relocation within the cell. After the axon crosses the midline, the repressive receptor is reactivated, keeping the axon from crossing back. Yang et al. (p. 944 , published online 26 March; see the Perspective by Kidd ) now show that in Drosophila the comm gene is regulated by the attractive receptor known as Frazzled. The Frazzled protein thus functions in two ways: It initiates attraction in response to a ligand and it activates transcription of the comm gene, keeping the repressive signal out of the action.