Description

C. elegans srf-6 mutants were isolated using altered surface immunofluorescence as phenotype (Hemmer et al., 1991; Grenache et al., 1996). In Van Sciver et al., 2019, we showed by whole genome sequencing that three different srf-6 mutants carry mutations in gene nsy-1. Well-characterized mutant alleles of nsy-1 result in hermaphrodites that express the olfactory receptor gene str-2 in both AWC neurons (2AWC^ON, Troemel et al., 1999), unlike wild type hermaphrodites, which express str-2 asymmetrically in only one of the two AWC neurons (1AWC^ON, Troemel et al., 1999). Our sequencing results suggested that srf-6 mutants might have a similar 2AWC^ONphenotype.  We therefore examined srf-6(yj13) for its AWC phenotype.

In order to introduce an str-2::GFP marker into the srf-6 genotype, first srf-6(yj13) unc-4(e120) II and nsy-1(ok593) unc-4(e120) II double mutants were constructed as described (Hemmer et al., 1991).  Homozygous males carrying the construct kyIs140, which contains an str-2::GFP fusion integrated on chromosome I (Troemel et al., 1999), were mated with srf-6(yj13) unc-4(e120) II hermaphrodites, and an Unc F2 hermaphrodite expressing GFP in chemosensory neuron AWC was cloned.  An individual hermaphrodite descendant, all of whose offspring expressed GFP, was isolated to establish a strain of genotype kyls140 I; srf-6(yj13) unc-4(e120) II.  A strain of genotypekyls140 I; nsy-1(ok593) unc-4(e120) was constructed similarly. Adult hermaphrodites from these strains were examined in a fluorescent microscope for their AWC phenotype. Figure 1 shows that srf-6(yj13) adults exhibited a 2AWC^ON phenotype similar to that of nsy-1(ok593).

To test whether srf-6(yj13) and nsy-1(ok593) affect the same or different genetic functions, a complementation test was performed (Figure 1, last two lines).  Males of genotype srf-6(yj13) were mated with kyls140 I; nsy-1(ok593) unc-4(e120) II hermaphrodites, and non-Unc offspring were scored in a fluorescent microscope for the AWC phenotype.  The complementation heterozygotes showed a 2AWC^ON phenotype similar to that of nsy-1(ok593).  This result included data from two separate crosses.  In contrast, when wild type males were mated with kyls140 I; nsy-1(ok593) unc-4(e120) II hermaphrodites, the 1AWC^ONphenotype was observed.  These results included worms from one cross.

These results indicate that srf-6(yj13) and nsy-1(ok593) mutations do not complement each other for the 2AWC^ON phenotype, and together with the srf-6 mutant sequencing results (Van Sciver et al., 2019), we conclude that srf-6 and nsy-1 are the same gene.