Worm Breeder's Gazette 15(4): 40 (October 1, 1998)

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.

The Pristionchus HOX gene Ppa-lin-39 inhibits programmed cell death to specify the vulva equivalence group and is not required during vulval induction.

Ralf J. Sommer, Andreas Eizinger, Kwang-Zin Lee, Benno Jungblut, Anja Bubeck, Isabel Schlak

Max-Planck Institut für Entwicklungsbiologie, Abt. Zellbiologie, Spemannstrasse 35, 72076 Tübingen, Germany.

In Caenorhabditis elegans and Pristionchus pacificus the vulva equivalence
group is specified by the Hox gene lin-39. C. elegans lin-39 mutants are
vulvaless and the VPCs fuse with the surrounding hypodermis, whereas in P.
pacificus lin-39 mutants the VPCs die of apoptosis. Mechanistically, LIN-39
might inhibit non-vulval fate (cell fusion in C. elegans, apoptosis in P.
pacificus), promote vulval fate or do both.
        To study the mechanism of lin-39 function, we isolated cell death
mutations in P. pacificus and made double mutants between lin-39 and a cell
death defective mutation. To isolate cell death defective mutations in P.
pacificus, we made use of the fact that 7 of the 12 Pn.p cells in the
ventral epidermis die of PCD. In cell death defective mutations, no PCD
should occur in the ventral epidermis, a region of the worm body that can
easily be scored using Nomarski optics. We mutagenized wild-type animals
with EMS and analyzed the progeny of F2 clonal lines. The progeny of
approximately 3500 F2 hermaphrodites were examined and three recessive
mutations were isolated in which the ventral epidermal cells P(1-4).p and
P(9-11).p survived. The three mutations fall into two complementation
groups, that have been originally named Ppa-ipa-1 and Ppa-ipa-2 for
inhibitor of P-ectoblast apoptosis. However, further phenotypic
characterization indicated that the absence of cell death is not restricted
to the ventral epidermal region. To clone the P. pacificus homolog of
ced-3, we performed PCR using primers to the highly conserved C-terminal
portion of Cel-ced-3. To determine whether Ppa-ipa-1(tu79) or
Ppa-ipa-2(tu80, tu81) correspond to mutations in Ppa-ced-3, we sequenced
the coding region of Ppa-ced-3 in the mutants. This sequence analysis
showed that the strain tu79 contains a point mutation at Pro417 resulting
in a missense mutation, indicating that the Ppa-ipa-1 mutant phenotye
results from mutations in Ppa-ced-3. Therefore, we rename Ppa-ipa-1 as
Ppa-ced-3. Surprisingly, P. pacificus ced-3; lin-39 double mutants form a
functional vulva in the absence of LIN-39 activity. Thus, in P. pacificus
lin-39 specifies the vulva equivalence group by inhibiting programmed cell
death. Furthermore, these data reveal an important difference in a later
function of lin-39 between the two species. In C. elegans, LIN-39 specifies
vulval cell fates in response to inductive RAS signaling, and in P.
pacificus LIN-39 is not required for vulval induction.