Worm Breeder's Gazette 10(3): 100
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.
Mutations in the gene lin-34 IV result in a dominant multivulva (Muv) phenotype that is characterized by the presence of multiple protrusions along the ventral side of the animal. lin-34 is one of only two genes in the vulval development pathway for which a dominant Muv allele has been identified. The dominant (and until recently only) allele of lin-34, n1046, is amber suppressible. However, the dominant effects of n1046 suggested that this allele is not null. We are now attempting to define the null phenotype of lin-34. In addition, we have characterized another putative lin-34 allele, n1700, which is also semidominant. The original allele of lin-34, n1046, was identified by Chip Ferguson in a general screen for vulval mutations. In contrast, n1700 was found by Dianne Parry as a dominant suppressor of the vulvaless ( Vul) phenotype of lin-10 mutants. We mapped n1700 and n1046 relative to mec-3, aps 0.03 mu to the left of dpy-20; n1046 has not been separated from dpy-20 and is within 0.03 mu of dpy-20. Deficiency mapping of n1700 showed that sDf2, which deletes dpy-20, uncovers n1700, whereas sDf8 and sDf10, both of which break to the left of dpy-20, do not uncover n1700. The n1046 and n1700 mutants have similar penetrances when homozygous (-95%), heterozygous with a wild-type chromosome (-20%) and heterozygous with a deficiency chromosome (-0%) at 20 C, and they also show a similar temperature dependence. The penetrance of n1046/n1700 is 95%. Taken together with the mapping data, these results suggest that n1700 is indeed a second allele of lin-34. Recently, in a screen for suppressors of let-341(n1613), Scott Clark isolated a semidominant Muv mutation, n1849, that appears to be a third allele of lin-34 (see the abstract by Scott Clark and Bob Horvitz in this Newsletter). The current alleles of lin-34 appear to be gain-of-function mutations that increase the level of wild-type lin-34 activity, because lin-34(sd)/lin-34(sd) homozygotes are more mutant than the lin- 34(sd)/+ heterozygotes, which in turn are more mutant than lin-34(sd) /Df heterozygotes. Furthermore, the wild-type phenotype of the heterozygote lin-34(sd)/Df suggests that it should be possible to obtain loss-of-function alleles by mutagenizing lin-34(sd) homozygotes and cloning phenotypically wild-type F1 progeny. In a screen of approximately 8,000 EMS-mutagenized haploid genomes, 17 strains suppressed for the penetrance of the Muv phenotype of n1700 were found. The ten strongest suppressors were analyzed further. All ten are extragenic, and seven are viable as homozygous suppressed strains in which the Muv phenotype is suppressed more than 80%. Three strains could not be homozygosed for the suppressor activity, and may define dominant suppressors with a recessive lethal phenotype. The characterization of these extragenic suppressors and efforts to obtain intragenic suppressors are continuing.