Drosophila central brain formation requires Robo proteins.

The Robo proteins have been extensively studied in the Drosophila embryonic ventral nerve cord, in which their expression level controls the midline crossing and optic lobe formation, but nothing is known about their activities during adult central brain formation. We have analyzed how Robo guidance cues influence central complex (CX) and mushroom body (MB) formation. Mutations of robo2 and robo3 confer a series of strong MB and CX defects. We found that the Robo2 and Robo3 proteins are expressed in two structures of the developing CX, the fan-shaped body (FB) and the noduli (NO), and by fibers across the central neuropile. We conclude that the Robo2 and Robo3 receptors play postembryonic roles during central brain formation.