The morphologies of C. elegans (Ce) and C. briggsae (Cb) are similar yet their genomes are highly divergent (1). One morphological structure common to Ce, Cb, and all known nematodes is the four-cell gonad primordium (2). The gonad primordium is composed of two somatic gonadal precursors (SGPs) and two primordial germ cells (PGCs). Two C2H2 zinc-finger genes, tra-1 and ehn-3, act redundantly to control the first division of the SGPs in Ce (3).TRA-1 is the Ce homolog of the Ci/GLI family of zinc finger transcription factors that controls embryonic patterning and cell division (4). In Ce, tra-1 is best known as a regulator of sex determination. This function is retained in Ce, Cb, and the nematode satellite species Pristionchus pacificus although sequences outside the zinc finger binding domains are highly divergent (5,6). On the other hand, the role of tra-1 in gonadogenesis is currently known only in Ce based upon preliminary evidence derived from a Cb tra-1 allele.The ehn-3 gene has no obvious ortholog in other nematode species. Instead, ehn-3 appears to be a member of a new family of zinc finger genes in Ce. The zinc fingers and gene structure of ehn-3 appear to be most similar to R08E3.4. In addition, R08E3.4 has highly conserved orthologs in other metazoans. RNAi of R08E3.4 and other ehn-3 paralogs indicates only R08E3.4 exacerbates ehn-3 gonadogenesis defects. Therefore, it appears that ehn-3 has arisen by duplication of R08E3.4 in the Ce lineage thereby providing the opportunity to understand the evolution of gene families and genetic redundancy. PCR-deletion screens for relevant mutants in Ce and Cb are underway. Preliminary results and relevant interactions between C2H2 zinc finger genes will be reported.(1) Stein LD, Bao Z, Blasiar D, Blumenthal T, Brent MR, et al. (2003) PLoS Biol 1(2): e45.(2) Chitwood, B.G, Chitwood, M.B., 1950. Introduction to Nematology. University Park Press, Baltimore.(3) Mathies et al. (2004) Development 131, 4333-4343.(4) Zarkower,D. and Hodgkin,J. (1992) Cell, 70, 237249.(5) de Bono, M., Hodgkin, J. (1996) Genetics, 144: 587-595.(6) Pires-daSilva, A., Sommer, R.J. (2004) Genes Dev. 18(10):1198-208.

Affiliations:
- Department of Biology, University of Maryland, College Park, MD
- Genetics, NCSU, Raleigh, NC