  Signal transduction pathways are largely conserved throughout the animal
kingdom. The repertoire of pathways is limited and each pathway is used in
different intercellular signaling events during the development of a given
animal. For example, Wnt signaling is recruited, sometimes redundantly with
other molecular pathways, in four cell specification events during
Caenorhabditis elegans vulva development, including the activation of vulval
differentiation. Strikingly, a recent study finds that Wnts act to repress
vulval differentiation in the nematode Pristionchus pacificus, demonstrating
evolutionary flexibility in the use of intercellular signaling pathways.
