Figure 4. Infrared-laser induction allows characterization of embryonic guidance defects in sax-3 and vab-1 mutants.

(a) Embryonic imaging of anterior amphid axon growth and failure to turn into the nerve ring in sax-3(ky123). Induction performed at AB64 in ABplaapa. Inset: magnified image of starred region showing forking and retraction of axons during growth. Time, minutes from comma stage. (b) The initiation time of axon outgrowth is not affected in sax-3 mutants. n=15 embryos for WT, n=23 embryos for sax-3(ky123). (c) Anterior nerve-ring placement is not pronounced in sax-3 mutants. Distance measured from nose tip to nerve ring in 2-fold embryos. n=15 embryos for WT, n=18 embryos for sax-3(ky123). (d) Embryonic imaging of amphid neurons in WT for comparison and vab-1(dx31) showing lateral trajectory. Time as in a. (e) Model for timing compensation in nerve-ring entry in vab-1 mutants. (f) Axon trajectories during nerve-ring entry are shorter in vab-1 mutants, and the dorsal turn occurs later. n=4 embryos each for wild-type and vab-1(dx31).