Worm Breeder's Gazette 7(2): 46
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.
We have recently begun to analyze a series of genes with the property that mutations in these genes individually can result in a wild-type phenotype but in certain pairwise combinations produce a Multivulva (Muv) phenotype. The Muv phenotypes of these strains are similar: hermaphrodites usually have a functional vulva and two large protrusions, one anterior and one posterior to the vulva; males also have ventral protrusions. Our attention was drawn to this phenomenon by the observation that two individually silent mutations, lin-8(n111) II and lin-9(n112) III, were responsible for the phenotype of the Muv strain CB1322 (Horvitz and Sulston, Genetics, 96, 435, 1980). A third such mutation, lin(n766) III, was discovered after mutagenizing the strain MT1312, which contains the lin-12 Vulvaless allele n676. Numerous Muvs were isolated during this experiment, and all proved to be synthetics. All of these synthetic Muv strains contained a silent mutation (named 'n766') linked to n676. Thus the original strain MT1312 was presumably of the genotype n766 n676. We are pursuing the analysis of these silent Muv mutations to answer the following questions. How many genes can mutate to silent Muv alleles? What is the nature of these silent Muv alleles? If these alleles are not null mutations, what are the null phenotypes of these genes? What roles do these genes play in vulva formation? Seventeen synthetic Muv mutations have been obtained from mutageneses of the three isolated silent alleles n111, n112 and n766. These new silent mutations have been mapped and tested for complementation with appropriate markers. These 17 mutations fall into five complementation groups. The table below lists the seven mapped genes now known to have silent alleles. In addition we have isolated 35 uncharacterized synthetic Muv strains by mutagenizing lin- 15(n767) and lin(n751), two of the above seventeen alleles. [See Figure 1] Two genes, lin-8 II and lin-15 X, have both silent and visible Muv alleles. The visible alleles but not the silent alleles behave in various heterozygous combinations like deficiencies, suggesting that the visible alleles result in the null phenotypes of these loci. lin- 15 alleles include visibles, temperature-sensitive (ts) visibles, silents, ts silents and ts silents with maternal effects. The ts visible allele n765 ( wild-type at 15 C, maternal effect Muv at 20 C, and Muv at 25 C) does not have wild-type activity at 15 C, as it acts as a silent allele, interacting with lin(n751) II to give a Muv phenotype. This result is consistent with the hypothesis that lin-15 silent alleles are hypomorphs, i.e. result in a reduction but not in a total loss of gene activity. Silent Muv alleles are recessive, i.e. in all pairwise combinations tested, hermaphrodites of the genotype m1/m1; m2/+, where m1 and m2 are silent alleles in different genes, are wild type. The only exception so far is lin(n766) III, as certain m1/m1; n766/+ hermaphrodites are sometimes Muv. However, in many cases the addition of a single copy of another silent allele to give the genotype m1/m1; m2/+; m3/+ results in a Muv phenotype ( less severe than that of either homozygote) . These observations suggest that the synthetic Muv phenotype results from the cumulative reduction in activity of genes that are either partially redundant in function or that act sequentially in a developmental pathway.