Worm Breeder's Gazette 15(1): 48 (October 1, 1997)

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 homeotic gene lin-39: regulation and evolution of nematode epidermal cell fates

Andreas Eizinger, Ralf J. Sommer

Max-Planck Institut fuer Entwicklungsbiologie, Abt. Zellbiologie, Spemannstrasse 35/V, 72076 Tuebingen, Germany

The non-vulval ventral epidermal cells P(1,2,9-11).p, undergo cell
fusion with the embryonically derived epidermal syncytium hyp7 in C.
elegans and other Rhabditidae. In contrast, in Pristionchus and other
species of the Diplogastridae, the non-vulval cells [P(1-4,9-11).p] die
of programmed cell death indicating that a change in cell fate
specification occurred in the evolutionary lineages leading to these
species. In C. elegans, the homeotic gene lin-39 prevents the central
cells from adopting the non-vulval fate and promotes vulval cell fate
instead. In C. elegans lin-39 mutants, P(3-8).p undergo cell fusion
resulting in a vulvaless phenotype.
        We obtained the Pristionchus homolog of lin-39 by PCR with
degenerate primers within the homeodomain and used this fragment to
screen genomic and cDNA libraries. This gene is similar in organization
and size to the lin-39 gene of C. elegans but contains one additional
        From an EMS-mutagenesis screen of approximately 40 000 gametes
we isolated more than 50 Pristionchus vulva defective mutants, 17 of
which have a vulvaless phenotype (WBG, 14, #4, 42). By cell lineage
analysis, two different phenotypes can be distinguished among the 17
vulvaless mutants. In five mutants the vulvaless phenotype is caused by
cell death of P(5-8).p. Complementation analysis revealed that three of
these five mutants, tu2, tu29 and sy374, belong to one gene and are all
linked to the visible mutation Ppa-dpy-1. One mutant, sy376 is unlinked
to Ppa-dpy-1 and complements tu2, tu29 and sy374. Hermaphrodites of the
fifth mutant, sy319, never formed ventral protrusions or vulvae and
thus, cannot be mated. In  the 12 other mutants, P(5-8).p survided but
did not divide, resembling the phenotype of gonad-ablated wild-type
animals. We analyzed the complete lin-39 coding region and at least 20
bp on either side of exon splice sites in the five mutants exhibiting
cell death of P(5-8).p and found point mutations in tu2, tu29, sy374
and sy319 introducing early stop codons. In agreement with suggested
nomenclature we named the gene Ppa-lin-39. No mutation was found in
sy376, which has been named Ppa-ped-12. The vulvaless phenotype of
Ppa-lin-39 is recessive and segregates with normal Mendelian
inheritance. Ppa-lin-39 mutations cause a vulvaless phenotype of
variable expressivity. The mutations sy319 and tu2 display a high
penetrance of embryonic and early larval lethality and P(5-8).p undergo
programmed cell death in nearly all analyzed mutant animals. In
contrast, in the two alleles, tu29 and sy374, about 30% of the vulval
precursor cells survive: In 100 tu29 mutant animals analyzed, 69 of
potential 300 VPCs survived, 45 of which differentiated into vulval
cells later in development. The remaining 24 cells had an epidermal
fate and did not divide.