Fig. 2. Longitudinal migration defects in unc-53 mutants. (A) The wild-type excretory canal. Two posterior canals extend from the excretory cell on each side along the lateral cord from the head to the tail. The boxes show the regions represented in B,C. These are DIC photomicrographs of adult worms showing the trajectory of the excretory canal (arrowheads). (B) In the wild type, the canal stops at the level of the anus (arrow). (C) An unc-53(n152) mutant, with a canal that stops at the level of the vulva (arrow). (D) The wild-type ALN and PLN projections. ALN and PLN send anteriorly directed axons up to the head along the sublateral dorsal and ventral cords, respectively. The box shows the region represented in E-H. These are fluorescence photomicrographs of adult wild-type (E,G) and unc-53(n152) mutant (F,H) worms expressing a pA::GFP reporter construct, showing the trajectory of an ALN (E,F) or PLN (G,H) axon (arrows). (F) The ALN axon has stopped its anterior outgrowth before the mid-body and sends several dorsal branches directly to the dorsal cord (arrowhead). (H) The PLN axon has stopped its anterior outgrowth before the mid-body and sends several dorsal branches to the ventral cord (arrowhead). c, cell body; pag, pre-anal ganglion. Scale bars: 10 µm.