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.

Search For Exploding Vulvae.

R.E. Palmer, P.W. Sternberg

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.