Figure 5 .

Model for the role of semaphorin-1a and UNC-6 signaling pathways during ray 1 positioning. SMP-1, SMP-2, and PLX-1 are part of a single pathway that functions in parallel to a pathway comprising UNC-6, UNC-40, and UNC-5. SMP-1 and UNC-6 ligands send a permissive signal to PLX-1 and UNC-40 receptors, required cell autonomously in ray structural cells. In wild-type males, individual ray cell groups form and separate on the anterior–posterior axis. This process is dependent on MAB-20–mediated signaling (green) (as well as the PLX-2 receptor and other unknown components—see Ikegami et al. 2004) since ray cell groups tend to cluster with adjacent cell process groups in mab-20 mutants. This MAB-20/PLX-2–dependent ray separation (green) is normally inhibited by the semaphorin-1a and UNC-6 pathways (red). Loss of function in semaphorin-1a and UNC-6 signaling pathways results in an effective gain of function of MAB-20–mediated signaling in the ray 1 structural cells, which increases separation between ray 1 and ray 2 cell groups.