Worm Breeder's Gazette 13(3): 102 (June 1, 1994)

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.

Searching for downstream genes in the vulval induction pathway

Andy Golden, Paul W. Sternberg

Caltech, Division of Biology and HHMI, Pasadena, CA 91125

The signalling pathway leading to vulval induction now contains a large number of conserved proteins with striking similarity to the signalling proteins used in yeasts, Drosophila, and animals. The vulval induction pathway utilizes an EGF/TGF-alpha-like protein ( lin-3 ),a receptor tyrosine kinase ( let-23 ),an adaptor protein ( sem-5 ),a ras protein ( let-60 ),a raf kinase ( lin-45 ),and a MAP kinase ( sur-2 / mpk-1 ).Genetic analysis suggests that this signalling pathway, in response to the inductive signal LIN-3 ,acts to inhibit the negative regulator, LIN-1 ,at the bottom of this signalling cascade. Mutations in the lin-1 gene result in Multivulva animals. To identify downstream components of this signalling pathway, we have started to screen for suppressors of this Multivulva phenotype. We expect that the pathway will branch at or after lin-1 and thus we sought suppressors with partial or no phenotypes on their own.

We screened 25,000 haploid genomes and are characterizing a number of candidate suppressors. The allele e1777 was used. While amber-suppressible, this allele displays a strong Multivulva phenotype on its own but is suppressed to wild type by sup-7 .The F2 of mutagenized Po's were screened for the presence of non-Multivulva animals or egg-laying defective/Vulvaless animals. Three classes of suppressed animals were recovered. The first class contains 5 Generation Vuls, the second class contains 3 lines that are suppressed to wild type, and the third class contains two lines that are suppressed to Vulvaless. We have focused on the 3rd class. This class of suppressors is distinct from those found by Edwards & Horvitz [WBG 8(1), 11.].

The third class of mutants suppresses the lin-1 ( e1777 )Multivulva phenotype to Vulvaless. At most, 2 vulval precursor cells are induced in these animals. These animals are extremely penetrant for the egg-laying defect. Interestingly, both of these recessive suppressors, when out-crossed from the lin-1 background, are not Vulvaless. They display no obvious vulval induction defects, though are disrupted in vulval morphogenesis; the vulvae either "leak" or burst as adults. Both Vulvaless lines have been reconstructed using multiply-backcrossed lines crossed back into lin-1 ( e1777 ).S up130 maps to the left arm of S up130 does not suppress the Multivulva phenotypes of lin-15 ( n309 )or let-60 ( sy130 gf)animals. The other suppressor, S up396 ,is still being mapped, but appears to complement S up130 .S up130 ,but not S up396 ,also displays a penetrant P12 .pa-to-P11.ptransformation in the ventral hypodermis, similar to what has been observed in many Vulvaless alleles of genes in this pathway. The observation that these 2 suppressors cause a Vulvaless phenotype in a lin-1 mutant background but not in a wild-type background suggests that there may be some redundancy at this part of the pathway. Likewise, these observations may suggest that the pathway branches somewhere near lin-1 .