title: Evolution of the Drosophila feminizing switch gene Sex-lethal.
abstract: In Drosophila melanogaster, the gene Sex-lethal (Sxl) controls all aspects of female development. Since melanogaster males lacking Sxl appear wild type, Sxl would seem to be functionally female specific. Nevertheless, in insects as diverse as honeybees and houseflies, Sxl seems not to determine sex or to be functionally female specific. Here we describe three lines of work that address the questions of how, when, and even whether the ancestor of melanogaster Sxl ever shed its non-female-specific functions. First, to test the hypothesis that the birth of Sxl's closest paralog allowed Sxl to lose essential ancestral non-female-specific functions, we determined the CG3056 null phenotype. That phenotype failed to support this hypothesis. Second, to define when Sxl might have lost ancestral non-female-specific functions, we isolated and characterized Sxl mutations in D. virilis, a species distant from melanogaster and notable for the large amount of Sxl protein expression in males. We found no change in Sxl regulation or functioning in the 40+ MY since these two species diverged. Finally, we discovered conserved non-sex-specific Sxl mRNAs containing a previously unknown, potentially translation-initiating exon, and we identified a conserved open reading frame starting in Sxl male-specific exon 3. We conclude that Drosophila Sxl may appear functionally female specific not because it lost non-female-specific functions, but because those functions are nonessential in the laboratory. The potential evolutionary relevance of these nonessential functions is discussed.
authors.affiliation: Department of Molecular and Cell Biology, University of California, Berkeley, California 94720-3204, USA. sxlcline@berkeley.edu
authors.forename: Thomas W
authors.initials: TW
authors.lastname: Cline
authors.forename: Maia
authors.initials: M
authors.lastname: Dorsett
authors.forename: Sha
authors.initials: S
authors.lastname: Sun
authors.forename: Melissa M
authors.initials: MM
authors.lastname: Harrison
authors.forename: Jessica
authors.initials: J
authors.lastname: Dines
authors.forename: Louise
authors.initials: L
authors.lastname: Sefton
authors.forename: Lisa
authors.initials: L
authors.lastname: Megna
mesh_terms: D000818:Animals; D005075:Biological Evolution; D029721:Drosophila Proteins / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000502:physiology; D005260:Female; D005812:Genes, Switch; D008297:Male; D008969:Molecular Sequence Data; D009154:Mutation; D012333:RNA, Messenger / Q000032:analysis; D016601:RNA-Binding Proteins / Q000235:genetics*; D019849:Sex Determination Processes; D012737:Sex Factors; D013045:Species Specificity
chemical_list: D029721:Drosophila Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; C067777:Sxl protein, Drosophila