Identification and Characterization of Novel Components in UNC-6/Netrin Signaling

UNC-6/Netrin guides circumferential migrations along the dorso-ventral axis in C.elegans. Its receptors, UNC-40/DCC and UNC-5, mediate both attraction and repulsion of migrating cells or growth cones from sources of UNC-6. seu-2(ev523)and seu-3(ev555) (suppressor of ectopic unc-5) were identified as suppressors of ectopic UNC-5 in the touch receptor neurons(Colavita and Culotii, 1998). Like other components of UNC-6 signaling, seu-2 and seu-3 have roles not just in the migration of axon growth cones, but also in the repulsive migration of other cell types, specifically the distal tip cells (DTCs). Similar to observations in the touch receptor neurons, both seu-2 and seu-3 are able to suppress ectopic expression of the UNC-5 receptor in the DTCs. Genetic analysis of seu-2; seu-3 double mutants reveals that these genes function within the same signaling pathway for repulsive unc-6 guidance. seu-2 also appears to act in attractive unc-6 guidance. Mutations in seu-2 result in ventral to dorsal axon guidance defects in the HSN and ray 1 neurons. Double mutant analyses of seu-2 with either unc-40 or unc-6 null mutations exhibited HSN and ray 1 axon guidance defects at similar penetrance to either single mutant. These results suggest that seu-2 functions in the attractive unc-6-unc-40 dependent signaling pathway for HSN and ray 1 axon guidance. seu-2 was found to encode a G protein coupled receptor. Whole genome sequencing was used to identiy that seu-3 encodes the novel protein K09C6.9. K09C6.9 is predicted secreted protein that is expressed throughout development. Taken together, the phenotypes, method of isolation and genetic interactions of seu-2 and seu-3 make them interesting candidate mediators of UNC-6 signaling. I utilized genes, such as seu-2 and seu-3, to further elucidate other signaling components governing cell migration and axon guidance.Ph