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Abstract

To study the molecular mechanisms underlying changes in cell fate specification during evolution, we started a genetic analysis of vulva development in Pristionchus. Pristionchus has a four day life-cycle, is easily cultured on OP50 and has six chromosomes by DAPI staining. In a small genetic pilot screen, more than 50 morphological mutants, representing the typical spectrum known from Caenorhabditis, have been isolated (Fund. Appl. Nemat. 19, 511-522). In a large screen of 40 000 gametes we have isolated 49 vulval defective mutants. Based on phenotype we can distinguish four groups of mutants, as well as two mutants with a unique phenotype (this includes the previously described ped-5 mutant). Group I: These mutants are lineage defective. In some mutants, P6.p adopts a 2o or hybrid fate instead of the 1o fate. However, cell ablation experiments indicate that these mutants are not lin-12(d)-like, as an AC is present and no differentiation was seen after gonad-ablation. Group II: These mutants have phenotypes similar to the previously described ped-6 mutant. Altogether 9 mutants have been isolated. Cell lineage analysis and cell ablation experiments indicate a different penetrance of individual mutants. Characterization is ongoing. Group III: These mutants are similar to the previously describedped-4 mutant. This group is surprisingly big, containing 12 mutants. Cell ablation experiments suggest that different subgroups of mutants can be distinguished. In some mutants only P(7,8).p, in others also P(5,6).p can differentiate after ablation of the gonad. However, we can not rule out, that these differences are based on the different penetrance of allelic mutations. Characterization is ongoing. Group IV: Mutants exhibiting a vulvaless-phenotype. Altogether, 17 mutants have been isolated that vary dramatically in penetrance. As in C. elegans, two types of vulvaless-phenotypes can be distinguished: In one group, VPCs adopt the 3o fate as in AC-ablated animals, in the other group, VPCs undergo programmed cell death as the more anterior and posterior epidermal cells of Pristionchus.