lin-3 is a gene necessary for the Vulval Precursor Cells (VPCs; a.k. a. P(3-8).p) to form the vulva in response to a graded inductive signal from the anchor cell. In hermaphrodites carrying Vulvaless ( Vul) alleles of
lin-3, induction of the VPCs is lowered or absent such that the vulva can not form and the animal is unable to lay eggs. We are interested in
lin-3 because epistasis tests between Vulvaless and Multivulva mutations affecting vulval development indicate that
lin-3 acts early in the pathway of vulval development. In addition, other alleles of
lin-3 have lethal and sterile phenotypes, indicating that
lin-3 has functions other than vulval induction. A F1 screen for new
lin-3 alleles was carried out to determine its null phenotype.
lin-3(
e1417); 90) males were mated to EMS-mutagenized
unc-24(
e138) 38)
dpy-20(
e1282) hermaphrodites and the F1 cross progeny were screened for egg-laying defective worms. Since
e1417/Df is viable, null alleles could be recovered in this screen. Three early larval lethal alleles (
sy51,
sy52,
sy53) of
lin-3 were found among 10,000 F1 progeny. A similar F1 screen by Chip Ferguson ( Genetics 110:17-72 1985) of 20,000
e1417/? F1 generated the lethal allele
n1059 and the sterile/larval lethal allele
n1058. Because larval lethal alleles are recovered more commonly than Vulvaless alleles in these screens, we believe that larval lethality is the null phenotype. Denise Clark et al. at Simon Fraser, in their analysis of lethals on LG IV, identified two late larval mutations,
s751 and
s1263, allelic to
lin-3. In agreement with the hypothesis that the null phenotype of
lin-3 is early larval lethal, they showed that the phenotype of
s751/Df and
s1263/Df is also early larval lethal ( Genetics 119: 345-353 1988). We are pursuing two approaches to clone
lin-3. Our first approach is to generate transposon-induced alleles of
lin-3. So far, one putative Tc-induced allele,
sy91, was detected by mating
lin-3(
e1417); 90) males to RW7096 [
mut-6 lin-3(+) 192::Tc1) ] hermaphrodites and picking nonUnc egg- laying defective F1. In contrast to the alleles found in the EMS F1 screens, this allele confers a Vul phenotype.
sy91 is currently being backcrossed to see if a new Tc band can be correlated with the Vul phenotype. Our second approach is to map
lin-3 with respect to cloned DNA in an attempt to define a region of DNA that must contain
lin-3. We have been mapping
lin-3 to sP5, an RFLP on the right end of the contig L122, to determine whether L122 extends far enough to cover lin- 3. 22 Vul nonDpy recombinants were picked from
lin-3(
e1417) 362) /BO heterozygotes. All the recombinants possessed the N2 version of sP5. Therefore sP5 is probably to the left of, or close and to the right of,
lin-3. We are currently examining recombinants in the
mec-3 to
lin-3 interval to determine the map order.