Studies into vulva formation in nematodes have provided insights into key developmental mechanisms and their evolution. Now, on , Yi and Sommer reveal that different regulatory networks specify the cells that form the vulva (the vulva equivalence group, VEG) in Pristionchus pacificus and Caenorhabditis elegans. In both nematodes,establishment of the VEG from the middle of the ventral epidermis requires the Hox gene lin-39. In C. elegans, the anterior and posterior non-vulval epidermal cells fuse with the hypodermis (a process indirectly regulated by lin-39) but, in P. pacificus, these cells die. Yi and Sommer isolated gev-2, a vulvaless mutant of P. pacificus, and show that gev-2 is the P. pacificus pax-3 gene (Ppa-pax-3). Ppa-pax-3 is a direct target of Ppa-LIN-39 and regulates the survival of the VEG precursors but induces the death of the posterior epidermal cells, they report. Thus, a different regulatory network in P. pacificusspecifies the VEG than in C. elegans, a finding that sheds new light on the evolution of fate specification.
