Worm Breeder's Gazette 13(5): 26 (February 1, 1995)
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.
HHMI and the Division of Biology, Caltech. Pasadena CA 91125.
The hermaphrodite vulva is formed from three of six posterior ectodermal cells (Pn.p cells). The three Pn.p cells (P5.p, P6.p, and P7.p) have two distinct fates. One difference between the two fates is the attachment of the cells to the ventral hypodermis. After three rounds of division, all the progeny of P6.p are not attached to the ventral hypodermis while half the progeny of P5.p and P7.p remain attached to the ventral hypodermis. Certain mutations and mutant combinations result in worms in which all three of Pn.p cells adopt the fate of P6.p, i.e. their progeny are not attached to the ventral hypodermis. In many instances, these mutants are lethal because when the vulval cells are not attached to the ventral hypodermis the worms explode at the vulva during the L4-adult molt. We sought to identify additional genes that when mutated would result in this phenotype. We performed an F1 clonal screen looking for dead worms in which the worms had exploded at the vulva during the L4 - adult molt. We screened 12,000 haploid chromosome sets and identified three mutants that exhibited an exploding vulval phenotype. All three mutants were recessive and incompletely penetrant for the vulval defect with between 40-75% of the homozygotes exploding. Two of the three mutants were allelic to the lin-1 mutant and the third mutation, sy329, defined a new gene. For both lin-1 alleles approximately 5percent lethality was observed, however, the penetrance of the exploding vulval phenotype varied between the alleles (70percent of sy321 homozygotes exploded and 25percent had a multi-vulval phenotype while in sy289 45percent of the homozygotes exploded and the other 50percent had a multi-vulval phenotype). Linkage analysis placed the sy329 mutation on LGI. Deficiency and three-factor mapping placed the sy329 between unc-13 and lin-10. sy329 in trans to the deficiencies nDf24 or nDf25 was indistinguishable from sy329 homozygotes. Approximately 40percent of sy329 hermaphrodites had exploding vulvae. An additional 15percentof the worms had protruding or multi-vulvae. Vulval lineage analysis of sy329 revealed that 40percent of the hermaphrodites had extra non-adherent vulval tissue (P6.p-like). Often additional Pn.P cells also formed vulval tissue. These vulval defects were suppressed by mutations in the well characterized signaling pathway required for vulval formation, i.e. lin-3, lin-7, and lin-45. sy329 hermaphrodites and males are sterile and exhibit several somatic gonad defects. There is no germ cell differentiation in sy329 hermaphrodites and males. Microscopic examination of sy329 hermaphrodites with Nomarski optics revealed that the germ cell nuclei, and presumably the cells, would fuse and form extremely large cells. DAPI staining of sy329 gonads showed that these large germ cells contained a massive excess of chromosomal DNA. In sy329 hermaphrodites, the distal tip cells (DTC) and the anchor cell were noticeably enlarged. The enlarged DTC phenotype was highly penetrant whereas the enlarged AC phenotype was less penetrant. In addition, it was not uncommon to observe 2 DTC per gonad arm and in some animals 2 AC were also observed. Since the AC is required for the formation of the vulva we postulate that the enlarged AC may be responsible for the extra vulval induction observed in sy329.