Vulva formation in Pristionchus pacificus relies on continuous gonadal induction

One of the best known features of vulva development in Caenorhabditis elega ns is the induction of vulval precursor cells by the gonadal anchor cell. I nduction is crucial for the initiation of pattern formation within the C. e legans vulva equivalence group, and it is therefore surprising to find that this aspect of vulva formation, in particular, varies greatly among nemato des. In some species which form vulvae in the posterior body region, no gon adal signal is necessary for vulva induction. In other nematodes, such as P anngrolaimus, Oscheius, and Rhabditella, vulva formation depends on two tem porally distinct gonadal inductions which specify the different cell fates. Here we report our analysis of vulva induction in Pristionchus pacificus, a species which has recently been used as a genetic system to analyze the e volution of vulva development. Cell ablation studies in P. pacificus show t hat another mode of vulva induction exists. P. pacificus vulva formation de pends on a continuous gonadal induction that starts several hours after hat ching and continues until the birth of the anchor cell, some 20 h later. Mu tations defective in gonadal induction result in the absence of vulva diffe rentiation, suggesting that only one signaling system is involved in the,go nadal-epidermal interaction. This new mode adds further to the great variet y of gonadal inductions among nematode species.