title: The gene Sex-lethal of the Sciaridae family (order Diptera, suborder Nematocera) and its phylogeny in dipteran insects.
abstract: This article reports the cloning and characterization of the gene homologous to Sex-lethal (Sxl) of Drosophila melanogaster from Sciara coprophila, Rhynchosciara americana, and Trichosia pubescens. This gene plays the key role in controlling sex determination and dosage compensation in D. melanogaster. The Sxl gene of the three species studied produces a single transcript encoding a single protein in both males and females. Comparison of the Sxl proteins of these Nematocera insects with those of the Brachycera showed their two RNA-binding domains (RBD) to be highly conserved, whereas significant variation was observed in both the N- and C-terminal domains. The great majority of nucleotide changes in the RBDs were synonymous, indicating that purifying selection is acting on them. In both sexes of the three Nematocera insects, the Sxl protein colocalized with transcription-active regions dependent on RNA polymerase II but not on RNA polymerase I. Together, these results indicate that Sxl does not appear to play a discriminatory role in the control of sex determination and dosage compensation in nematocerans. Thus, in the phylogenetic lineage that gave rise to the drosophilids, evolution coopted for the Sxl gene, modified it, and converted it into the key gene controlling sex determination and dosage compensation. At the same time, however, certain properties of the recruited ancestral Sxl gene were beneficial, and these are maintained in the evolved Sxl gene, allowing it to exert its sex-determining and dose compensation functions in Drosophila.
authors.affiliation: Centro de Investigaciones Biológicas, 28040 Madrid, Spain.
authors.forename: Esther
authors.initials: E
authors.lastname: Serna
authors.forename: Eduardo
authors.initials: E
authors.lastname: Gorab
authors.forename: M Fernanda
authors.initials: MF
authors.lastname: Ruiz
authors.forename: Clara
authors.initials: C
authors.lastname: Goday
authors.forename: José M
authors.initials: JM
authors.lastname: Eirín-López
authors.forename: Lucas
authors.initials: L
authors.lastname: Sánchez
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D003001:Cloning, Molecular; D017124:Conserved Sequence; D004175:Diptera / Q000196:embryology / Q000235:genetics* / Q000378:metabolism; D004303:Dosage Compensation, Genetic; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism; D004331:Drosophila melanogaster / Q000235:genetics; D004625:Embryo, Nonmammalian; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D005804:Genes, Lethal; D008571:Men; D008969:Molecular Sequence Data; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012313:RNA / Q000378:metabolism; D012318:RNA Polymerase I / Q000378:metabolism; D012319:RNA Polymerase II / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D019849:Sex Determination Processes; D014158:Transcription, Genetic
chemical_list: D029721:Drosophila Proteins; D016601:RNA-Binding Proteins; C067777:Sxl protein, Drosophila; D012313:RNA; D012319:RNA Polymerase II; D012318:RNA Polymerase I