Worm Breeder's Gazette 14(1): 33 (October 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 VII: Mutants of Pristionchus with extra or missing Pn.p-ectoblasts.

Ralf J. Sommer^1,2, Paul W. Sternberg¹

A dramatic reorganization in the ventral cord of Pristionchus pacificus
with respect to presumed ancestors involves cell death of P(1-4).p and
P(9-11).p. The vulva is formed by P(5-7).p and the remaining ectoblast,
P8.p, is not a vulva precursor cell. In a genetic screen for egg laying
defective mutants we found mutants with increased or decreased numbers of
Pn.p-ectoblasts. Some of the ped (for P-Ectoblast Determination) mutant
phenotypes are described below. We have assigned these mutations to
separate genes based on complementation analysis (except for ped-2).

ped-l(sy312): Some of the posterior Pn.p ectoblasts, P(9-11).p, survive.
This phenotype is variable. If the ectoblasts are present, they form
vulva-like structures in the posterior body region in addition to the
normal central vulva. AC ablation does not influence vulva differentiation
of these celIs .
ped-2(sy319): The central ectoblasts P(5-8).p are absent, whereas the
hypl2 cell is present. We have observed a few embryonic cell deaths in the
central ventral cord. However, this analysis is complicated by high
embryonic lethality. More than 95% of the eggs are lethal, and most of the
remaining larvae die as L1. In the few surviving larvae, the VC neurons
(P(5-8).aap in wild-type) die, like the corresponding cells in the
anterior and posterior body region. Altogether, the ped-2 phenotype
resembles the C. elegans ceh-20 phenotype (Chen & Stern, C. elegans Mtg.
1995, pp20).
ped - 6(sy345): P(3,4).p survive and become ectoblasts. This phenotype is
highly penetrant. The two additional cells form vulva-like structures with
one or two additional anterior invaginations. AC ablations reveal that in
ped-6 not only P(3,4).p but also P(5-7).p differentiate in an AC
independent manner, indicating that ped-6 is a multivulva mutation,
possibly similar to lin-15.
ped-5(sy344): P(3,4).p survive as in ped-6, but do not form vulva-like
structures. A series of VPC ablation experiments indicate that P(3,4).p
are vulva precursor cells. After ablation of P(5,6).p, a normal vulva can
be formed by P(3,47).p. Thus, for the anterior region ped-5 reconstitutes
the vulva equivalence group seen in C. elegans, indicating a homeotic
transformation .
ped-4(sy346): P8.p undergoes additional vulva differentiation in appr. 40%
of animals. A weaker effect is present on P7.p also. AC ablation show,
that both cell can differentiate in an AC independent manner. Thus, both
cells of the original ventrolateral pair P7/8L,R are affected.

In summary, we can use a genetic approach to identify molecular changes
accounting for cellular diversity.