Evolution of sex determination in caenorhabditis: unusually high divergence of tra-1 and its functional consequences.
The tra-1 gene is a terminal regulator of somatic sex in Caenorhabditis elegans: high tra-1 activity elicits female development, low tra-1 activity elicits male development. To investigate the function and evolution of tra-1, we examined the tra-1 gene from the closely related nematode C. briggsae. Ce-tra-1 and Cb-tra-1 are unusually divergent. Each gene generates two transcripts, but only one of these is present in both species. This common transcript encodes TRA-1A, which shows only 44% amino acid identity between the species, a figure much lower than that for previously compared genes. A Cb-tra-1 transgene rescues many tissues of tra-1(null) mutants of C. elegans but not the somatic gonad or germ line. This transgene also causes nongonadal feminization of XO animals, indicating incorrect sexual regulation. Alignment of Ce-TRA-1A and Cb-TRA-1A defines several conserved regions likely to be important for tra-1 function. The phenotypic differences between Ce-tra-1(null) mutants rescued by Cb-tra-1 transgenes and wild-type C. elegans indicate significant divergence of regulatory regions. These molecular and functional studies suggest that evolution of sex determination in nematodes is rapid and genetically complex.
de Bono
M
M
Medical Research Council Laboratory of Molecular Biology, Cambridge, England.
Hodgkin
J
J
D000595:Amino Acid Sequence; D000818:Animals; D030801:Animals, Genetically Modified; D001483:Base Sequence; D002107:Caenorhabditis / Q000235:genetics*; D017173:Caenorhabditis elegans / Q000235:genetics*; D029742:Caenorhabditis elegans Proteins; D018509:DNA, Helminth; D004268:DNA-Binding Proteins; D019143:Evolution, Molecular; D005260:Female; D015801:Helminth Proteins / Q000235:genetics*; D008565:Membrane Proteins / Q000235:genetics*; D008969:Molecular Sequence Data; D016296:Mutagenesis; D012333:RNA, Messenger; D017386:Sequence Homology, Amino Acid; D012732:Sex Determination Analysis; D014157:Transcription Factors; D019076:Transgenes; D014424:Turner Syndrome
D029742:Caenorhabditis elegans Proteins; D018509:DNA, Helminth; D004268:DNA-Binding Proteins; D015801:Helminth Proteins; D008565:Membrane Proteins; D012333:RNA, Messenger; D014157:Transcription Factors; C121025:tra-1 protein, C elegans