Fig. 1. Features of the C. elegans ventral nerve cord. The VNC in wild-type animals and consequences of microsurgical removal of PVT on VNC architecture are shown. Neurons that have terminated their axon outgrowth (PVQL/R, AVKL/R, RMEV, HSNL/R) are affected by laser removal of PVT or zig-4 mutation, such that their axons flip over the hypodermal ridge (ventral midline) into the opposite fascicle (Aurelio et al., 2002). The upper inset shows gene expression profiles in PVT (see text for references), the lower inset the expression pattern of several LIM homeodomain transcription factors in the tail ganglia of an L1 stage animals (Cassata et al., 2000; Hobert et al., 1998; Hobert et al., 1999b; Sarafi-Reinach et al., 2001; Way and Chalfie, 1989).