2002 European Worm Meeting abstract 44
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Institut Jacques Monod, Tour 43, 2 pl. Jussieu, 75251 Paris cedex 05,France
We compare vulval patterning mechanisms between Caenorhabditis elegans and Oscheius sp. 1 CEW1. In Caenorhabditis elegans, the pattern of Pn.p vulval precursor cell fates is set by several cell interactions: an inductive signal from the anchor cell and a lateral signal between Pn.p cells. In Oscheius sp. 1 CEW1, the same fate pattern is specified by two successive anchor cell inductions, first on P(5-7).p, and then on P6.p daughters.
In order to study vulval development in Oscheius, we performed genetic screens for egg-laying mutants and found the three following vulva development mutant categories. 1) We obtained numerous dov mutants, which show an abnormal number of division of vulval precursor cells (Dichtel et al., Genetics 2001). Similar mutants are scarce (and sterile) in C. elegans. 2) We also obtained many cov mutants (competence and/or centering of the vulva). 3) Unlike in C. elegans, we found few iov mutants (abnormal induction of vulval precursor cell fates), and they show different phenotype scompared to the C. elegans induction mutants. The vulval-defective screens in C. elegans and Oscheius thus show striking differences in the mutant phenotypes that were reached, which points to different evolutionary potentials. A corresponding greater variability in Pn.p division number of the 3° cells was observed in natural populations of Oscheius species (Delattre and Félix, Curr. Biol. 2001). Thus, these cell divisions are less robust against genetic variations in Oscheius.
In C. elegans, vulval induction occurs through the RAS/MAPKinase pathway. In order to study the role of this pathway in Oscheius, we used U0126, an inhibitor of MEK (a downstream effector of RAS). U0126 blocks the induction in C. elegans. In Oscheius sp. 1, both inductions are affected, suggesting that MEK could play a role in both steps of vulval induction.
Using anchor cell ablation experiments in dov and cov mutants that show a partial penetrance, we observed that the anchor cell influences the competence and the divisions of the Pn.p cells, in additionto inducing the vulval fates. We will present the epistatic relationships of the iov mutations with the cov/dov mutations, and the possible role of MEK in these different anchor cell roles in Oscheius.