Worm Breeder's Gazette 15(4): 23 (October 1, 1998)
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.
Department of Zoology, University of British Columbia, Vancouver, B.C. Canada
Embryos homozygous for null mutations in the unc-112 gene exhibit a Pat terminal phenotype. They arrest at the two-fold stage of embryogenesis and have severely disorganized body wall muscle (Williams and Waterston, 1994, JCB 124:475-490). In contrast, animals carrying the r367 allele are viable, although they do have severely disorganized body wall muscle and are paralyzed as adults. We have isolated several extragenic suppressors of unc-112(r367) by selecting well moving anmals from the progeny of mutagenized hermaphrodites. All of the suppressor mutations characterized are alleles of the dim-1 (disorganized muscle) gene which we have positioned between dpy-7 and dpy-6 on the X chromosome. These alleles are null mutations and are able to suppress the paralyzed phenotype of unc-112(r367) when either heterozygous (good suppression) or homozygous (better suppression). Thus, reduction or loss of dim-1 gene function results in suppression of unc-112(r367). Hermaphrodites homozygous for a dim-1 mutation on its own appear wild-type under the dissecting microscope. However, the body wall muscle is easily disrupted and appears disorganized when viewed under polarized light. The dim-1 gene corresponds to the C18A11.7 and C18A11.8 open reading frames identified by the C. elegans sequencing consortium. Although identified by Genefinder as two separate genes, sequencing of the cDNA clone YK399b7 obtained from Y. Kohara revealed that these ORFs are part of a single gene consisting of 12(?) exons with a rather large (3.5 kb) intron separating exons 6 and 7. We have identified the sequence alterations for three of the dim-1 alleles. One (ra111) is a 183 bp deletion that extends from the middle of exon 8 into the adjacent downstream intron, and the two remaining mutations (ra209 and ra114) delete the 3' end of the gene. The dim-1 gene encodes a novel 640 amino acid protein that is presumably required for myofilament lattice stability in the body wall muscle. The first 315 amino acids of this protein (encoded by exons 1 through 6) are not similar to any known protein whereas the remaining 325 amino acids constitute three immunoglobulin repeats similar to those found in Titin and UNC-22/Twitchin. The unc-112 gene maps to the left of unc-76 on LG V in the interval between the left breakpoints of the deficiencies, yDf9 and yDf11. We have rescued the mutant phenotype of unc-112(r367) with a 7.5 kb fragment subcloned from one of the cosmids in this region containing the C47E8.7 ORF plus 2.5 kb of upstream sequence. The C47E8.7( unc-112) gene encodes a 720 amino acid protein that is most similar to a human protein of unknown function called MIG-2 (J. Cell Sci. 107:227). A full length cDNA (YK12c6) obtained from Y. Kohara has been sequenced and the results confirm the gene structure predicted by Genefinder. This putative UNC-112 protein shares a short, ~50 amino acid region of homology with Talin, Band 4.1 and Ezrin which may be important for attaching these proteins to the plasma membrane.