Worm Breeder's Gazette 8(2): 49
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 continued our analysis of spontaneous mutations affecting unc-54. We are interested in studying the mechanisms of spontaneous mutagenesis, especially those involving transposable elements. We reported previously that unc-54 insertion mutations are undetectable in the N2 Bristol strain, arising at a frequency of less than 5x10+E-9. We have used similar selection techniques to isolate spontaneous unc- 54 mutations in the Bergerac (B0) genetic background. We thought that Tc1 might be transpositionally active due to its high copy number in Bergerac. Spontaneous unc-54 mutations occur in the Bergerac background at a frequency of approximately 1x10+E-6 per gamete (this is 3-fold higher than in the Bristol background). Eleven of 19 mutations are insertions of 1.6 kb within unc-54. Several different insertion sites are observed, but there is considerable clustering of insertions. Three of the inserts are known to be Tc1. Recombinant lambda clones carrying these unc-54 mutations hybridize to Tc1. The remaining eight insertions also appear to be Tc1 based on Southern blot data. Many of the insertions revert to unc-54+ in both germline and somatic cells. Germline excision results in stable reversion of the unc-54 mutant phenotype. It has been measured in one typical strain to occur at a frequency of 4x10+E-6. Somatic excision results in mosaic animals. When viewed by polarized light microscopy, these animals contain both mutant and wild-type muscle cells. For certain mutants, as much as 1% of the animals are mosaic for body wall and sex muscles derived from the M lineage. Southern blots indicate that both germline and somatic excisions of Tc1 are precise or nearly precise. Tc1 copy number per se is not responsible for Bergerac mutability. Strain DH424 has a Tc1 copy number similar to Bergerac. We have collected 29 spontaneous unc- 54 mutants in the DH424 genetic background. They occur at a frequency of 4x10+E-7 per gamete, and none of them are insertions.