The diversity of the Nematode species is enormous although the overall body plan of worms is conserved in evolution. We are interested in how such diversity was originated and whether we can identify specific changes in cell biological events (e.g. cell migration, cell division and cell fusion) responsible for morphological variability among Rhabditida species. Organogenesis of the vulva in the nematodes Caenorhabditis elegans and Pristionchus pacificus was described in detail (1,2). To study the evolution of vulva formation in related Rhabditida nematode species we participate in an international consortium studying differences in the molecular, lineage and cellular aspects of organogenesis (3). Ring shaped structures form the vulva in all studied species. We have found that different aspects of vulva formation such as cell migration, intratoroidal fusion sequence and final ring structure are diverse through the different species of the Rhabditida family. We also found a correlation between the vulval cell division orientation and the final number of vulval rings. While there is little variation in the number and structures of rings derived from the 1ry sublineage, the rings derived from the 2ry sublineage generate dramatic structural diversity. When primordial cells divide in the anterior-posterior axis, they give rise to two vulval rings. When the same cells divide in the left-right axis, they form one ring. The most external primordial cells form a single ring, independent of the axis of their division. We are creating a matrix of the data that will integrate with multidisciplinary findings from the other research groups of our consortium (Marie-Anne Felix, Ralf Sommer and David Fitch; see abstract by Kiontke et al.). In our search for evolution in the lab we have checked lin-11 mutant causing a cell transformation in the 2ry lineage. In lin-11 mutants, the cells that normally express the LLTN lineage pattern, transform to either LLLN or LLLL patterns. We predicted that according to our hypothesis, the L division might give 2 rings instead of 1 ring resulting from a T division. Indeed, we found lin-11 hermaphrodites with 8 rings instead of 7 in N2. (1) Development, 1999, 126, 691-699. (2) Dev Biol, 2004, 266, 322-333. (3) Supported by HFSP.

Affiliations:
- Section on Membrane Biology, LCMB, NICHD, NIH, Bethesda MD, USA
- Biology, Technion- IIT, Haifa, Israel