Essential for nerve cord development. Functions downstream of fra to control axon guidance across the central nervous system (CNS) midline. In embryos expressed in the brain and overlying head tissue. Expressed in the ventral nerve cord at the onset of commissural axon guidance toward the midline. Expression levels in the ventral nerve cord peak in 50 hour old embryos. By 52 hours expression becomes restricted and appears to be expressed specifically in neurons which cross the midline such as EG, RP1, RP3 and RP4. At 54 hours, when most commissural axons have crossed the midline, expression levels in the nerve cord was no longer detected. RNAi-mediated knockdown results in thinning or even complete loss of commissural axons in embryonic nerve cords. Belongs to the commissureless family.