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.
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 intron. 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.