T. Kidd et al., DOSAGE-SENSITIVE AND COMPLEMENTARY FUNCTIONS OF ROUNDABOUT AND COMMISSURELESS CONTROL AXON CROSSING OF THE CNS MIDLINE, Neuron, 20(1), 1998, pp. 25-33
commissureless and roundabout lead to complementary mutant phenotypes
in which either too few or too many axons cross the midline. The robo;
comm double-mutant phenotype is identical to robe alone, suggesting th
at in the absence of robe, comm is no longer required. Comm is express
ed on midline cells; Robe is expressed in a dynamic fashion on growth
cones and appears to function as an axon guidance receptor. robe funct
ion is dosage-sensitive. Overexpression of comm is also dosage-sensiti
ve and leads to a phenotype identical to robe loss-of-function. Comm c
ontrols Robe expression; increasing Comm leads to a reduction of Robe
protein. The levels of Comm and Robe appear to be tightly regulated to
assure that only certain growth cones cross the midline and that thos
e growth cones that do cross never do so again.