Figure 3.

Robo1 Fn1 and Fn2 are not required for regulation by Comm. Stage 16 embryos stained with anti-HA (green) and anti-HRP (magenta). Lower images show HA channel alone of the same embryos. (A–D) Embryos with one copy of the transgene as well as elav-GAL4 display normal Robo1 protein expression among the HA-tagged variants (arrows). (E–G) Homozygous transgenic embryos carrying elav-GAL4 and UAS-Comm show strongly downregulated HA expression among the slit-like collapsed axon scaffold (arrows with asterisks). (H) Robo1ΔFn3 is the only variant that is not downregulated on axons when Comm is misexpressed (arrow). Pairs of sibling embryos shown (A and E; B and F; C and G; and D and H) were stained in the same tube and imaged under the same confocal settings to ensure accurate comparison of HA levels between embryos. Fn, fibronectin type-III repeat.