Exogenous toxicants, such as harmful food substances, environmental contaminants, and exotoxins from infected microorganisms, as well as endogenous toxicants, such as free radicals from energy metabolic bi-products, are direct or indirect causes of aging and many age-related diseases that include cancers. The phase II enzyme family of glutathione S-transferases (GSTs) is recognized as playing a major protective role against exogenous and endogenous toxicants. We constructed gst::gfp fusion genes and used them to create transgenic C. elegans that responds well to many xenobiotics (such as methyl mercury, chloropropanols, acrylamide) by emitting a GFP signal in a dose- and time-dependent manner via the GST expression. To dissect the pathway leading to gst expression in response to xenobiotics, we isolated 24 independent abnormal gst-response mutations by screening about 3.5 times105 genomes of gst::gfp transgenic strains mutagenized with EMS. Complementation testing assigned them to four groups. Sixteen mutations of the largest group are all recessive and constitutively express gst in the whole body in the absence of xenobiotics. The second group of six recessive mutations constitutively expresses gst from body-wall muscle and pharynx only after the adult stage. The third has one dominant mutation with constitutively expressed gst in the whole body. The fourth has one recessive mutation expressing no gst in the presence of xenobiotics. We named these genes
xrep-1, -2, -3, and -4 (genes in xenobiotics response pathways), respectively.Conventional mapping linked
xrep-1 to LG I, and SNP mapping narrowed
xrep-1(
k1007) to within the cosmid clone D2030 (total of 704 recombinants inquired). Double-stranded RNA based on each of twelve genes within D2030 was used for soaking RNAi. The gene D2030.9 was selected, amplified, injected into
xrep-1 mutant animals, and completely rescued
xrep-1 mutant phenotypes. The gene
xrep-1 encodes WDR-23, a nematode homolog of the WD repeat-containing protein, which is also found in yeast, plants, and mammals. We continue to study these xrep genes, as we continue seeking for new crops of xrep mutants.