Worm Breeder's Gazette 6(1): 23
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 reported earlier that we had cloned four DNA fragments that hybridize strongly to Dictyostelium actin cDNA (WBG, Vol. 5, No. 1). We refer to these four fragments as C. elegans actin genes although we do not know that each is expressed as actin. Three of these genes are in a cluster. When the DNA's from Bristol and Bergerac strains are cut with several different restriction endonucleases and the DNA's hybridized on a Southern filter to 32P-labeled actin probe, distinctly different actin patterns can be observed between the two strains. We have used these interstrain differences in restriction endonuclease cleavage patterns as a phenotype for mapping the actin genes. We crossed Bergerac hemaphrodites with heterozygous dumpy males with dumpy markers representing the five different autosomal linkage groups. From each cross, about 70 to 100 F2 dumpy animals were picked, and grown up. Each dumpy stock therefore is assumed to be homozygous for the Bristol chromosome represented by the particular dumpy but randomly heterozygous for the other four unselected autosomes. F2 non-dumpy animals that did not segregate dumpy progeny were also collected from each cross and they are assumed to represent the recovery of the corresponding homozygous Bergerac autosomes. Because linkage group III is so big, two different dumpy markers were individually used. DNA was extracted from each of the twelve stocks, cut with HindIII, transferred to a nitrocellulose filter by the Southern technique, and hybridized to a 32P nick-translated C. elegans actin probe. DNA from strains in which chromosome V was retrieved by recovery of the dumpy marker showed only the Bristol pattern and the corresponding non-dumpy segregants displayed only the Bergerac pattern. DNA from all other ten strains displayed a hybrid pattern indicating random assortment of chromosome V. The X-linkage is being done with lon-1 but the experiment is not yet finished. We conclude at this time that the cluster of three C. elegans actin genes are on linkage group V. Three factor crosses have been carried out by crossing dpy-11 gerac, recovering the recombinant phenotypes, growing them to be sure each one represents a single recombination event, i.e. they initially segregate parental phenotypes, then picking the homozygous recombinant phenotype segregants and growing them up for DNA preparations. After restriction endonuclease cleavage, DNA was analyzed for the Bristol versus Bergerac pattern by hybridization on a Southern blot. Seven of eight dpy-11 recombinants showed the Bristol pattern and one showed the Bergerac pattern. One unc-76 recombinant showed the Bristol pattern and one showed the Bergerac pattern. We tentatively conclude at this point that the three linked actin genes are between dpy-11 and unc-76, near dpy-11. More three factor crosses are in progress. Bob Waterston has alerted us to unc-92 and we are going to try to zero it via Df-1. We still have not located the fourth unliked actin gene. We believe that this interstrain cross method will be generally applicable to mapping any gene for which a cloned probe exists and we are trying others.