The turtle gene functions non-cell autonomously in promoting motor axon branching. (A) Wild-type embryo stained with FasII antibody, showing the ISNb nerve branch innervating the cleft between muscles 6 and 7 (lower black arrow), muscle 13, and the cleft between muscles 12 and 13 (upper black arrow), the ISNd nerve branch (white arrow), and the TN nerve (arrowhead). (B) tutlex383 mutants have ISNb nerves that frequently fail to project final branches (black arrows), and many segments lack an ISNd (white arrow) but still posses a normal TN nerve (arrowhead). (C) Elav-Gal4 expression of the diffusible turtle isoform fully rescues both ISNb and ISNd nerve branch defects in tutlex383 homozygous embryos (arrows and arrowhead). (D, E) Both pan-neuronal Sca-Gal4 (D) and pan-skeletal muscle 24B-Gal4 and G14-Gal4(E and D, respectively) overexpression of turtle isoforms cause ISNb nerves to either excessively branch (black arrows) Yesor stall, cause the TNs to send out ectopic branches (arrowheads), and produce missing ISNd nerves (white arrows). (G) Quantification of the motor nerve defects seen in 55 to 60 A2 to A7 embryonic hemisegments in turtle mutants (tutlk14703, tutl10805, and tutlex383), in complementation testing (tutlex383/tutl10805), and in tutlex383 homozygotes with different turtle isoforms transgenically expressed using Elav-Gal4. Note that only the two diffusible isoforms rescue the mutant to near-wild type levels of motor axon pathfinding errors. The turtle gene functions non-cell autonomously in promoting retinal axon invasiveness and branching. (H) Adult wild-type head horizontal section showing retinal axons visualized with 24B10 antibody. Note normal optic chiasm (arrowhead) and regular array of R7 axon terminations (arrow). (I) tutlk14703 adult mutants have gaps in the R7 termination line (arrow) and an irregular chiasm (arrowhead). (J) The retinal axon defects in tutlex383/tutlk14703 are rescued when the diffusible turtle isoforms are transgenically expressed using the pan-neuronal driver Elav-Gal4. (K) Eye-specific GMR-Gal4 overexpression of the diffusible turtle isoforms in a wild-type background produces retinal axons that invade the cortex (asterisk), gaps in the R7 termination line (arrow), and some axons with extra branches (arrowhead). (L) tutlk14703 EGUF/hid mutant eyes have normal optic and R7 projections (L).
Al-Anzi and Wyman Neural Development 2009 4:31 doi:10.1186/1749-8104-4-31