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Genetic and molecular analysis of mutations in the unc-52 gene of Caenorhabditis elegans, and isolation of a suppressor, sup-38 Gilchrist, Erin J.


Mutations in the unc-52 gene in Caenorhabditis elegans have been grouped into four categories based on their mutant phenotypes and complementation patterns. Class 1 mutations result in gradual paralysis beginning in the late larval stages or early in adulthood. Animals homozygous for these alleles also exhibit gonadal disorganization which is reflected in their small and variable brood sizes. Class 2 mutations cause complete paralysis of the embryo, and developmental arrest at the two-fold stage of embryogenesis. The class 3 allele also results in arrest at the two-fold stage of development but these animals are not paralyzed, inspite of having disorganized muscle. Class 1 and class 3mutations complement one another, although both of them fail to complement the class 2 alleles. Class 4 alleles of unc-52were isolated as intragenic suppressors of class 1 mutations and confer a novel phenotype upon homozygous worms. These animals do not move as well as wild-type animals, and when their body wall muscle cells are examined using polarized light microscopy, they appear much thinner and more fragile than those of wild-type animals. Molecular examination of the different mutations has revealed that several of the class 1alleles are clustered in an exon near the 3' end of the gene, and that the class 3 mutation is located at the 5' end of theunc-52 locus. All the class 4 mutations are point mutations which eliminate the splice acceptor site of the intron upstream of the class 1 mutations. The unc-52 gene has been cloned and sequenced and is homologous to the vertebrate basement membrane component, perlecan. In an effort to examine the role of this basement membrane protein in muscle function, I have isolated intergenic suppressors of the class 1 unc-52 mutants. The suppressors are all alleles of a novel gene, sup-38. Animals homozygous for these suppressor mutations exhibit mild muscle abnormalities and severe to mild gonadal disorganization. Loss-of-function alleles of sup-38 were also isolated. These mutations are maternal-effect lethal, and they do not affect normal muscle structure or function.

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