Worm Breeder's Gazette 16(3): 20 (June 1, 2000)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
Dept. of Genetics, University of Pennsylvania School of Medicine, Philadelphia PA 19104
The Rho family GTPase Rac controls cytoskeletal re-organization and cell migration, and has been proposed to be a major target of Ras during oncogenic transformation. We are using C. elegans vulval development as a model system to study Rac function and the relationship between Rac and Ras. Vulval development involves several different events potentially influenced by Rac, including Ras-MAP kinase signaling, cell proliferation and cell migration.
C. elegans has three rac-like genes: mig-2, which controls neuronal cell migrations and axonal pathfinding (1), rac-1/ced-10 which controls cell corpse engulfment and distal tip cell migration (2), and rac-2, in which no mutations have been reported. We observed that mig-2(mu28lf) or ced-10(n1993lf) single mutants have normal vulval development, while ced-10(n1993); mig-2(mu28lf) or ced-10(RNAi); mig-2(mu28lf) double mutants have a variety of vulval defects, including missing VPCs (likely due to defects in P cell migration) and failure of secondary vulval descendants to migrate inward and stack during vulval invagination. In addition, the double mutants are severely uncoordinated ("coiler uncs") and throw various types of lethal progeny. Many of the ced-10; mig-2 phenotypes (including the vulval phenotypes) resemble those caused by activating alleles of mig-2 (1) or loss-of-function alleles of unc-73 (3). Thus, it appears that mig-2 and ced-10 have overlapping functions during multiple developmental processes including vulval morphogenesis, that mig-2(gf) alleles interfere with the functions of both genes, and that UNC-73 (a Trio GNRF, ref. 3) likely catalyzes guanine nucleotide exchange on both MIG-2 and CED-10. We are now using RNAi to test the involvement of other candidate Rac pathway components like Pak and PI3-kinase in vulval development.
Our preliminary results also suggest that Rac could play a role during Ras-mediated vulval induction. We’ve found that ced-10(RNAi) or mig-2(mu28lf) can each partially suppress the Multivulva phenotype of let-60(n1046gf), while the ced-10(RNAi); mig-2(mu28lf) double strongly suppresses the Multivulva phenotype. mig-2(mu28lf) also enhances the Vulvaless phenotype caused by two different let-60 hypomorphic alleles. Another initially intriguing result was our observation that mig-2(rh17gf) caused synthetic vulvaless and lethal phenotypes in a sur-8 mutant background; however, this result can be attributed to a linked ksr-1 mutation present in the NJ36 mig-2(rh17gf) mutant background.