Worm Breeder's Gazette 9(3): 39
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 are mapping a gene defined by adult-specific antigenic differences between Bristol (N2) and the varietal strain PA-l. These phenotypic differences were described previously (WBG V. 9, #1, p. 52). Stage-specific surface antigens may play a role in the host immune response to medically important parasitic nematodes. In addition, genes directly and specifically affecting adult surface antigen expression may respond to the action of major regulatory genes and may therefore provide specific genetic markers for heterochrony besides morphological characters already in use such as the adult alae and vulva. Adults of strain PA-l do not bind adult-specific rabbit antibodies prepared against N2 cuticle proteins. We analyzed the genetic differences that account for the observed surface antigen difference by performing hybrid crosses between N2 and PA-l. First, we determined that the N2 (antigen-positive) phenotype is dominant in Fl hybrids. N2 males were crossed with PA-l hermaphrodites or vice versa. Fl hybrid males were tested for adult-specific antibody binding. Individuals were scored for immunofluorescence; 97-100% of the Fl males in either cross were positive. N2 and PA-l male control samples showed 100% and 4% positive males, respectively. The similarity in results of the two reciprocal hybrid crosses further suggests that the phenotype is not determined in a sex-linked fashion. In similar crosses between N2 visibly marked (dpy or unc) strains and PA-l, we isolated outcross F2 segregants that were antigen- negative and bred true, like the PA-l parental strain. Their relative frequency suggested that the phenotype might be determined by a small number of genes. We therefore pursued linkage analysis in hybrid crosses using linkage markers on all 5 autosomes. dpy/+ or unc/+ males in the Bristol genetic background were crossed with PA-l. Outcross clones were identified as those segregating for the marker phenotype. Homozygous wild-type (nonmarker) segregant clones were established, and about twelve of these were screened for antibody binding by immunofluorescence. In the case of close linkage, most or all homozygous non-marker clones should show the non- recombinant, antigen-negative phenotype. Of all the markers tested, only unc-4(e120)II, and rol-1(e91)II showed linkage, with about 80% of clones in each case showing the antigen- negative phenotype. Thus, only linkage group II markers showed significant linkage. We have apparently identified a gene or cluster of genes on linkage group II that specifies the N2 adult surface antigen phenotype. Do strains such as PA-l carry allelic alternatives to the N2 antigen gene, or do they carry null alleles of the N2 gene? This is an intriguing question for further investigation.