Worm Breeder's Gazette 13(3): 99 (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.
lin-3 is the vulval inducing signal made by the anchor cell during C. elegans vulval development. It is a novel member of the epidermal growth factor (EGF) family and encodes a transmembrane protein with one extracellular EGF repeat. The extracellular region is predicted to be processed to form a soluble signal, which is sufficient to induce the vulva. Reduction of lin-3 activity causes a Vulvaless (Vul) phenotype, overexpression of lin-3 in transgenic animals results in a Multivulva (Muv) phenotype with a large abnormal vulva and smaller pseudovulvae. lin-3 expression in the somatic gonad is restricted to the anchor cell, beginning at the stage when vulva induction initiates. Using genetic screens, we are looking for genes that are required for proper expression and function of lin-3 ,for example, transcription factors, proteins required for lin-3 processing into a secreted signal, and cofactors. We may also recover new components of the vulva induction pathway downstream of let-23 in these screens.
syIs1 is a chromosomal integrant of a lin-3 transgene and has a dominant and fully penetrant Muv phenotype. We screened for suppressors of syIs1 by EMS mutagenesis. 23 independent suppressor mutants were obtained in a screen of 56,000 haploid genomes. These suppressors fall into several classes: 1). sy272 and 12 other alleles define a locus on LGV between dpy-11 and rol-3 .They suppress syIs1 to close to wild type and do not confer a vulva defect in an otherwise wild type background. The suppression of syIs1 is temperature-sensitive. sy272 is recessive when syIs1 is homozygous but dominant when syIs1 is heterozygous. sy272 does not suppress lin-15 (1f),suggesting it acts prior to let-23 .2). sy274 and 2 other alleles define a locus on LGX between dpy-8 and dpy-6 .They also suppress syIs1 to close to wild type and are recessive. The suppression is also temperature sensitive. 3). M3 .13defines a locus on LGX. It is a recessive suppressor of syIs1 and suppresses it to close to wild type. It also has interactions with both sy272 and sy274 .4). sy286 confers a highly penetrant Vul phenotype in syIs1 background. It also has male spicule defect, moderate sterility and slight lethality. In more than 50% of the animals P7 .pand P8 .premain undivided. 5). M6 .13also confers a Vul phenotype in syIs1 background. 6). We recovered two strains with lin-12 (d)-likephenotype, that is, five to six pseudovulvae and no anchor cell. We also recovered one let-23 allele. We did not recover deletion of syIs1 ,and this suggests that integrated transgene can be used for suppressor screen.
We also EMS mutagenized lin-3 ( n378 )/ lin-3 (1059),a highly penetrant Vul strain. From a screen of 30,000 haploid genomes, 7 independent suppressors were recovered. They suppress the Vul phenotype to various extent. Some of them are dominant and may be linked to the original lin-3 mutation. At least three are extragenic and recessive.