Fig. 2.

CrGAP RNAi enhances guidance defects in slit, robo/+ embryos. Stage 16 embryos are stained with the mAb1D4 to reveal the three FasII-positive longitudinal axon pathways. SRE indicates slit¹,robo⁵/+; elav-GAL4/+.(a) In WT embryos, the FasII-positive axon pathways never cross the midline. (b) In slit¹, robo⁵/+ transheterozygous embryos, the medial (innermost) longitudinal pathway occasionally crosses at the midline (arrows). (c) In slit¹,robo⁵/+ transheterozygotes, reducing CrGAP gene dose with the RNAi transgene significantly enhances the ectopic crossing defects. (d) Histogram showing the quantification of the midline crossing phenotypes in each of the indicated genotypes. The percentages of segments that showed ectopic crossing are shown. The number of segments scored in each genotype (n) was 275, 173, 297, 126, 136, 96, 159, and 136. *, P < 0.01, in Fisher's exact test. A second line of CrGAP^RNAi, UAS-CrGAP^RNAi-2/TM3 also shows significant enhancement of the crossing phenotype (53.3% crossing, n = 137) (data not shown).