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Figure 5


Fig. 5. Mutations in ß-spectrin genetically interact with the Slit-Robo pathway. All embryos were dissected at late stage 16 and were stained with anti-Fas2 Mab. Anterior is up. In all panels, arrows indicate sites of medial axons ectopically crossing the midline and arrowheads point to lateral longitudinal bundle breaks. (A) ß-spectrin null embryos exhibit ectopic Fas2-postitive axons crossing the midline and lateral longitudinal breaks. (B) slit, robo/+; elavGal4/+ (SRE) heterozygous embryos contain approximately two to three Fas2-positive bundles crossing the midline. (C) Removing ß-spectrin dramatically and specifically enhances the SRE defect. Note the effect is synergistic and not simply additive. (D) The genetic interaction seen in C can be suppressed by expressing wild-type UAS-ß-Spectrin in all postmitotic neurons with elavGal4. Note that approximately two to three ectopic crosses (arrows) are still observed as a result of the SRE background; however, the distance between medial longitudinal bundles has widened and the lateral breaks have disappeared. (E) ß-spectrin hypomorphic embryos have mild axon guidance defects. In this embryo, one medial longitudinal bundle crosses the midline (arrow) and lateral breaks are still observed (arrowheads). (F) Similar to the null allele, hypomorphic ß-spectrin alleles also show specific dose-dependent genetic interactions in a slit,robo/+ heterozygous background. (G) Quantification of single mutant phenotypes and genetic interactions. a, em6/+ (n=15); b, em6/Y (n=18); c, slit, robo/+; elavGal4/+ (n=19); d, em6/Y; slit,robo/+; elavGal4/+ (n=9); e, em6/Y; slit,robo/UAS-ßSpec; elavGal4/+ (n=23); f, G0198/Y (n=14); g, G0198/Y; slit,robo/+ (n=10); h, G0074/Y (n=13); i, G0074/Y; slit,robo/+ (n=11). Asterisk denotes a significant difference between genotypes d and b, and d and e (P=2.71x10-8 and 1.13x10-11, respectively; two-sample Student's t-test). Double asterisk denotes a significant difference between genotypes g and f (P=1.73x10-6; two-sample Student's t-test). Triple asterisk denotes a significant difference between genotypes i and h (P=2.60x10-6; two-sample Student's t-test). There is no significant difference between genotypes c and e. Error bars indicate s.e.m.