Fig. 4. Loss of SDN-1 affects the guidance and left/right choices of commissural motoneurons. (A) Schematic of DD and VD motoneurons. (B,E) DD/VD commissures in young adults and (C,D) embryonic DD commissures in the L1 larva. (B) Ventral nerve cord (VNC) view of an sdn-1(zh20) animal. D-type motoneurons inappropriately grow out on the left side of the animal (arrowhead) or stop prematurely before reaching the dorsal nerve cord (DNC) (arrows). L, left side; R, right side. (C) Six DD commissures form a continuous dorsal nerve cord in the wild-type L1 larva. (D) In sdn-1 null mutants, DD commissures branch prematurely and fail to reach the DNC (arrow). (E) D-type motoneuron development analyzed for: (1) circumferential outgrowth of DD/VD commissures to the DNC; (2) left/right choice to exit the VNC. (1) N represents the total number of commissures scored. Right and left denote the percentage of commissures that reach the DNC when growing out on the correct (right side) and incorrect side (left side), respectively. Note that guidance is considerably more affected if axons grow out on the wrong side of the animal. (2) N represents the number of animals analyzed. Each column gives the percentage of animals that show the indicated amount (1-8) of commissures inappropriately exiting the VNC on the left side. Scale bars: 10 µm.