The nematode even-skipped homolog vab-7 regulates gonad and vulva positionin Pristionchus pacificus

In free-living nematodes, developmental processes like the formation of the vulva, can be studied at a cellular level, Cell lineage and ablation studi es have been carried out in various nematode species and multiple changes i n vulval patterning have been identified. In Pristionchus pacificus, vulva formation differs from Caenorhabditis elegans with respect to several auton omous and conditional aspects of cell fate specification. To understand the molecular basis of these evolutionary changes, we have performed a genetic analysis of vulva formation in I! pacificus. Here, we describe two mutants where the vulva is shifted posteriorly, affecting which precursor cells wi ll form vulval tissue in P! pacificus, Mutant animals show a concomitant po sterior displacement of the gonadal anchor cell, indicating that the gonad and the vulva are affected in a similar way. We show that mutations in the even-skipped homolog of nematodes, vab-7, cause these posterior displacemen ts. In addition, cell ablation studies in the vab-7 mutant indicate that th e altered position of the gonad not only changes the cell fate pattern but also the developmental competence of vulval precursor cells. Investigation of Cel-vab-7 mutant animals showed a similar but weaker vulva defective phe notype to the one described for Ppa-vab-7.