Worm Breeder's Gazette 10(3): 59

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.

Progress on the Genetics and Cloning of lin-3

Russell Hill and Paul Sternberg

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.