Caenorhabditis elegans cog-1 locus encodes GTX/Nkx6.1 homeodomain proteins and regulates multiple aspects of reproductive system development.

The development of the reproductive system in Caenorhabditis elegans is a well-established model system for patterning and organogenesis. We report the characterization of the cog-1 gene, mutations in which cause novel phenotypes in late patterning in vulval lineages, establishment of the vulva-uterine connection, development and function of the spermathecal-uterine junction, and the development of vas deferens-proctodeal connection in the male. We positionally cloned cog-1 and found that it encodes a homeobox protein most similar to the mammalian GTX and Nkx6.1 proteins. Analysis of cog-1 transcripts revealed that cog-1 is likely a complex locus with two promoters. Two mutant alleles of cog-1 differentially affect alternative transcripts and cause different phenotypes, suggesting that the two forms of cog-1 have distinct functions in C. elegans.