Worm Breeder's Gazette 14(3): 29 (June 1, 1996)
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 MCD Biology, Univ. of CO, Boulder CO 80309-0347
The two sex myoblasts (SMs) in the hermaphrodite are born during the L1 larval stage in the posterior region of the animal, one on the left side and one on the right. The SMs then migrate approximately 65 mm anteriorly during the L2 stage to occupy very precise final positions flanking the gonad in the mid-body region, near the site of the future vulva. Two separable components of SM guidance have been described: a gonad-independent mechanism sufficient for the initial anterior migration to the mid-body region, and a gonad-dependent mechanism required for precise final positioning (Thomas et al., 1990). We have demonstrated a role for a Ras-mediated signal transduction pathway in controlling SM migration. Loss-of-function mutations in let-60 ras, ksr-1, lin-45 raf, let-537/mek-2 or sur-1/mpk-1 cause the SMs to adopt a broadened range of final positions that resembles what is seen in gonad-ablated wild-type animals, while constitutively active let-60 ras(G13E) transgenes allow fairly precise SM positioning to occur in the absence of the gonad. A recent mosaic analysis of let-60 ras has demonstrated that let-60 ras is required within the SMs to control proper positioning. Based on these results, we propose a model in which gonadal signals normally stimulate let-60 ras activity in the SMs, thereby making the SMs competent to sense or respond to positional cues in the mid-body environment. Several observations suggest that let-60 ras could have additional roles in SM guidance as well: 1) Several unusual but apparently reduction-of-function let-60 alleles [WBG 13(1), 13(3)] cause a striking posterior displacement of the SMs similar to that caused by mutations in egl-15 FGFR (DeVore et al., 1995); 2) The SMs sometimes adopt abnormal dorsal postions in let-60 ras and other Ras pathway mutants; and 3) Mosaic animals lacking let-60 ras in the SMs appear to have a somewhat different SM distribution than mosaic animals lacking let-60 ras in both the SMs and gonad. We are currently pursuing these observations. DeVore, D. L., Horvitz, H. R. and Stern, M. J. (1995). Cell 83, 611-620. Thomas, J. H., Stern, M. J. and Horvitz, H. R. (1990). Cell 62, 1041-1052.