Homozygous eye-specific gek^omb1080 clones (generated using the eyFLP method) cause specific defects in R cell axon target selection in adult flies. The cartridges (barrel-like structures of 6 post-synaptic axon targets) are disorganised in gek^omb1080 mutants, with individual cartridges displaying variable numbers of axon terminals. As in wild type, the majority of R1-R6 axons target to the lamina and only rare fibers extend into the medulla. 96% of R7 axons and 99% of mutant R8 axons innervate the correct layer in the medulla compared to 100% in controls.

In both homozygous gek^omb1080 and transheterozygous gek^omb1080/Df(2R)e03819-f02302 third instar larval R cell axon fascicles above the lamina plexus are occasionally clumped and the lamina plexus appears broken and varies in thickness. This phenotype is seen in all brains examined. Additionally, occasional bundles of axons are observed extending into the medulla that are thicker than usual. A slightly increased number of R2-R5 cell axons project into the medulla in gek^omb1080/Df(2R)e03819-f02302 compared to wild type. Animals in which only R cells are homozygous for gek^omb1080 (using eyFLP clones) exhibit a similar but weaker phenotype. No transformations of R1-R6 neurons into R7-R neurons are observed in homozygous gek^omb1080 eye discs.

Homozygous gek^omb1080 pupal stage R cell clones extend out of the retina into the brain, fasciculate normally and stop in the lamina. However, once in the lamina, mutant photoreceptors often make errors in columnar targeting, making projections to one or more incorrect target cartridges in addition to the correct target or failing to extend at all. Only 35% of R cells make the correct extension, 35% mistarget and 30% fail to extend. Targeting errors are observed in all R1-R6 cells. Homozygous gek^omb1080 R cell growth cones display 20% fewer filopodia and are approximately 30% smaller than corresponding control growth cones. The ommatidia appear morphologically normal.

In gek^omb1080/gek^NP5192 third instar larvae R cell axon fascicles above the lamina plexus are occasionally clumped and the lamina plexus appears broken and varies in thickness. This phenotype is seen in all brains examined. Additionally, occasional bundles of axons were observed extending into the medulla that are thicker than usual.

Expression of gek^{ΔCC.Scer\UAS} under the control of Scer\GAL4^Glass38-1 in gek^omb1080/Df(2R)e03819-f02302 mutant third instar larvae results in early termination of many R cell growth cones, with large clumps appearing in the optic stalk and the distal lamina.

Expression of gek^{ΔPH.Scer\UAS} under the control of Scer\GAL4^Glass38-1 in gek^omb1080/Df(2R)e03819-f02302 mutant third instar larvae results in early termination of many R cell growth cones, with large clumps appearing in the optic stalk and the distal lamina.

Expression of gek^{ΔCH.Scer\UAS} under the control of Scer\GAL4^Glass38-1 in a gek^omb1080/Df(2R)e03819-f02302 mutant third instar larvae results in early termination of many R cell growth cones, with large clumps appearing in the optic stalk and the distal lamina.

gek[+]/gek^omb1080 is a suppressor | partially of egg chamber phenotype of RhoGAP19D^unspecified