Fig. 6. unc-119(ed3) DD axon branches are produced by secondary growth cones. (A) Sprouting from DD axons increased with time. Lateral sprouts (black dots) extending from DD axons were observed before 15 hours in unc-119(ed3) mutants expressing GFP in the GABA motor neurons. Sprout activity peaked at 15 hours post-hatching (33%) and was nearly absent by 30 hours after hatching. Growth cones extending from DD axons (open squares) increased in number after 10 hours, by 20 hours 44% of DD axons scored had supernumerary growth cones. Axon branches (+) became visible 30 hours after hatching. VD growth cone migration occurred between 15 and 30 hours after hatching in unc-119(ed3) mutants (gray field). During this analysis we did not observe sprouts or axonal growth cones in wild-type animals at any time (n=7). (B) Axonal growth cones produced supernumerary branches in unc-119(ed3) mutants expressing GFP in the GABA motor neurons. Time-lapse analysis of an unc-119(ed3) axon showed an axonal growth cone (arrow, 0:00) extending multiple branches towards the dorsal nerve cord (arrow, 0:24 to 1:02). One of these branches projected to the dorsal nerve cord (arrow, 0:46). Note that the axon extended along the dorsal midline retracted (compare arrowheads in 0:00 and 1:02). Below is a schematic of the growth cone. Scale bar is 5 µm.