In embryonic stage 16 robo3
mutants, the medial axonal fascicle misroutes across the midline, whereas the intermediate and lateral fascicles extend laterally, some longitudinal glia migrate over the midline whereas some retain their lateral positions (100% penetrance). In robo3
embryos the pCC/vMP2 fascicle is affected, collapsing over the midline (100% penetrance). In robo3
mutants at stage 12.1 only the dMP2/MP1 fascicle extends along its normal trajectory (with 27.7% penetrance) and curves medially slightly more than in wild-type only at the most posterior end. At stage 14, the vMP2/pCC fascicle is always collapsed over the midline in robo3
, but the dMP2/MP1 fascicle can form normally.
-expressing axons are seen crossing back and forth across the midline in homozygous embryos, in contrast to wild type. Heterozygous embryos show only extremely rare midline crossing defects.
Some, but not all, interface glia migrate over the CNS midline. Longitudinal connectives are somewhat closer to the midline than in wild type, and the pCC/MP2 fascicle may cross the midline. Expression of roboScer\UAS.cKa
driven by Scer\GAL4s.gcm
rescues the lateral positions of the glia but does not rescue the axonal misrouting across the midline of robo3
positive neurons, including the pCC, cross the midline in robo3
"Fuzzy commisure" phenotype in embryonic central nervous system.