Originally published as Genetics Published Articles Ahead of Print on February 1, 2008.

Genetics, Vol. 178, 1415-1429, March 2008, Copyright © 2008
doi:10.1534/genetics.107.073668

Comparative Genetics of Sex Determination: Masculinizing Mutations in Caenorhabditis briggsae

Danielle F. Kelleher^*,1, Carlos Egydio de Carvalho^,1,2, Alana V. Doty^*, Marnie Layton^*, Andy T. Cheng^*, Laura D. Mathies, Dave Pilgrim and Eric S. Haag^*,3

^* Department of Biology, University of Maryland, College Park, Maryland 20742, Department of Biological Sciences, University of Alberta, Edmonton, Alberta T6G 2E9, Canada and Department of Genetics, North Carolina State University, Raleigh, North Carolina 27695

³ Corresponding author: Department of Biology, Bldg. 144, University of Maryland, College Park, MD 20742.
E-mail: ehaag{at}umd.edu

The nematodes Caenorhabditis elegans and C. briggsae independently evolved self-fertile hermaphroditism from gonochoristic ancestors. C. briggsae has variably divergent orthologs of nearly all genes in the C. elegans sex determination pathway. Their functional characterization has generally relied on reverse genetic approaches, such as RNA interference and cross-species transgene rescue and more recently on deletion mutations. We have taken an unbiased forward mutagenesis approach to isolating zygotic mutations that masculinize all tissues of C. briggsae hermaphrodites. The screens identified loss-of-function mutations in the C. briggsae orthologs of tra-1, tra-2, and tra-3. The somatic and germline phenotypes of these mutations are largely identical to those of their C. elegans homologs, including the poorly understood germline feminization of tra-1(lf) males. This overall conservation of Cb-tra phenotypes is in contrast to the fem genes, with which they directly interact and which are significantly divergent in germline function. In addition, we show that in both C. briggsae and C. elegans large C-terminal truncations of TRA-1 that retain the DNA-binding domain affect sex determination more strongly than somatic gonad development. Beyond these immediate results, this collection of mutations provides an essential foundation for further comparative genetic analysis of the Caenorhabditis sex determination pathway.

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