Worm Breeder's Gazette 14(1): 63 (October 1, 1995)
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.
Dept of Embryology, Carnegie Institution of Washington, 115 W. University Pkwy, Baltimore, MD 21210
Mutations in let-858 result in embryonic lethality with arrest occurring at the 2-3 fold stages. We have cloned and sequenced the minimal genomic fragments capable of rescuing this lethality and have determined that let-858 encodes a 2.8 Kb mRNA that appears to be enriched in the germline and gives rise to a ~90 kD protein. Interestingly, while the genomic constructs can rescue the lethality of let-858 alleles, the rescued animals grow to sterile adults with a variety of germline defects. Given the apparent germline enrichment for the let-858 mRNA, it is likely that this sterility reflects the inefficiency of expression of, and hence poor rescue by, extrachromosomal arrays in the germline. Database searches for proteins similar to LET-858 have identified a human cDNA with an 85% similarity (65% identity) over a stretch of 110 amino acids. Of course, as these things usually go, the cDNA is for a protein of unknown function. In addition, an Arabadopsis cDNA (with the same amount of information known as the human protein) also shares significant similarity with let-858 (66% similar, 46% identity). We feel that this is yet another case where C. elegans. can be used as a model for simpler systems, such as Arabadopsis and H. sapiens. We have constructed an in-frame fusion inserting GFP coding sequence into let-858 and have found it to be ubiquitously expressed in all somatic cell-types, and that it is localized to the nuclei of these cells. This construct, like the native genomic construct from which it was derived, also rescues the lethality of mutant alleles, but not the sterility defect. This correlates with the absence of GFP fluorescence in the germline of rescued animals. Recent attempts to achieve efficient germline expression of this construct using a modified transformation protocol have met with some success (see next abstract), and we can now strengthen the correlation between germline expression of let-858 and the rescue of fertility: in all cases where germline expression of let-858::gfp were observed in mutant animals, the animals were rescued for both the lethality and sterility defects. We conclude from these results that let-858 encodes a protein that has essential functions in both the soma and the germline. We are currently raising antibodies to confirm that it provides these functions in the nucleus.