Semidominant mutations in the genes
lin-24 IV and
lin-33 IV can cause degeneration of the Pn.p cells. Since the vulval precursor cells are a subset of the Pn.p cells, these mutations result in a vulvaless ( Vul) phenotype. These degenerations are independent of the functions of the
ced-3 and
ced4 genes, which are required for programmed cell death. However, these degenerations depend on three of the genes known to be involved in the engulfment of cell corpses:
ced-2, ced-S, and
ced-10. These results suggest that the changes in the Pn.p cells caused by the semidominant mutations in
lin-24 and
lin-33 lead to engulfment of the Pn.p cells, which causes their deaths. We have sought the null phenotype of these two genes by mutagenizing mutant hermaphrodites with EMS or X-rays and looking for revertants among the Fl and F2 progeny. We have isolated three intragenic revertants for each gene. We believe that a null mutation in
lin-24 results in a wild-type phenotype. We have recently isolated a deficiency, nDf41, that fails to complement markers both left and right of
lin-33. Since none of the
lin-33 revertants behaves as nDf41 does in trans to
lin-33(sd), we do not know the null phenotype of lin- 33. From the revertant screen described above, we isolated a small deletion,
n2256, which fails to complement
lin-33. We also isolated a duplication, nDpS, which extends from
unc44 to
unc-26 and fails to complement
lin-33 but does complement the lethality of the deletion
n2256. Using cosmids from the region of a contig that encompasses lin- 33 as determined by our mapping of N2/N62 RFLPs, we have found a 5kb EcoRI fragment that is missing in the nl O43
n2256; nDpS strain. We are injecting cosmids from this region into a strain of genotype lin- 33(revertant)
lin-24(sd). Because a
lin-33(revertant) mutation suppresses the
lin-24(sd) phenotype, this strain is not Vul. We hoped that by injecting cosmids containing
lin-33(+), we would find transformed animals that are Vul. Unfortunately, none of the cosmids injected resulted in Vul transformed animals. Further analysis is under the way.