Worm Breeder's Gazette 13(5): 19 (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.

Evolution of Vulva Formation: Part V: Starting Genetics in Pristionchus (Diplogasteridae).

Ralf J. Sommer, Seong-Youn Kim, Paul W. Sternberg

HHMI & California Institute of Technology, Division of Biology 156-29, Pasadena, CA

Vulva development in Pristionchus is different from Caenorhabditis
with respect to early and late specification events (WBG,
13, 107). Most dramatic is the reduction of the number of
P-ectoblasts in the central body region to four, P(5-8).p.
Although P(5-7).p form the vulva with a lineage very similar
to Caenorhabditis, a major difference is the fact that
P8.p is not a VPC. To get a better understanding of the processes
leading to this presumably highly derived character state,
we started genetic analysis in this species. Furthermore,
we wanted to see what kind of phenotypes can be found in a
genetic F2 screen standard to Caenorhabditis.
The generation time of Pristionchus is 3 days at 20¡ C; the
average number of progeny is 200. Males can be obtained
with a frequency of 50 per plate under starving conditions
(mass transfer of worms from plate to plate). We screened
approx. 6600 genomes in a standard F2 screen, looking for
morphological mutations. We identified 20 mutations
with an Unc phenotype, 21 mutations with a Dpy phenotype,
l mutation with a Rol phenotype and 99 mutations with an
Egl phenotype, and backcrossed them. All mutants except
for most of the Egl mutants are in permanent culture. Except
for one case we cannot correlate these mutants to specific
mutants in Caenorhabditis. Concerning the Caenorhabditis
unc-22 gene, we observed a mutant in Pristionchus, called
unc-l, that has the same twitching phenotype as unc-22.
Furthermore, mutants with this phenotype were observed
with a very high frequency, consistent with the molecular
characterization of unc-22. We observed ca. 25 mutants
with the twitching phenotype in this screen of 6600 gametes.
Our primary interest was in the Egl mutants which could
include phenotypes with an altered specification of the
ventral cord ectoblasts. Nomarski analysis of Egl mutants
after backcrossing revealed four vulvaless mutations:
P(5-8).p do not divide in these mutants, thus they resemble
the phenotype of gonad ablated wild-type animals.
More surprising was the finding of 12 mutants where the
number of P-ectoblasts in the ventral cord is altered in
comparison to wild-type. Some mutants cause a reduction,
others cause an increase in the number of P-ectoblasts.
We call these Ped mutants for P-Ectoblast Determination
mutants. They will be described, together with the corresponding
cell ablation experiments, in the next WBG.....