RESUMO
In Drosophila melanogaster and in Sciara ocellaris dosage compensation occurs by hypertranscription of the single male X chromosome. This article reports the cloning and characterization in S. ocellaris of the gene homologous to maleless (mle) of D. melanogaster, which implements dosage compensation. The Sciara mle gene produces a single transcript, encoding a helicase, which is present in both male and female larvae and adults and in testes and ovaries. Both Sciara and Drosophila MLE proteins are highly conserved. The affinity-purified antibody to D. melanogaster MLE recognizes the S. ocellaris MLE protein. In contrast to Drosophila polytene chromosomes, where MLE is preferentially associated with the male X chromosome, in Sciara MLE is found associated with all chromosomes. Anti-MLE staining of Drosophila postblastoderm male embryos revealed a single nuclear dot, whereas Sciara male and female embryos present multiple intranuclear staining spots. This expression pattern in Sciara is also observed before blastoderm stage, when dosage compensation is not yet set up. The affinity-purified antibodies against D. melanogaster MSL1, MSL3, and MOF proteins involved in dosage compensation also revealed no differences in the staining pattern between the X chromosome and the autosomes in both Sciara males and females. These results lead us to propose that different proteins in Drosophila and Sciara would implement dosage compensation.
Assuntos
Proteínas Cromossômicas não Histona , DNA Helicases , Proteínas de Ligação a DNA , Dípteros/genética , Mecanismo Genético de Compensação de Dose , Proteínas de Drosophila , Drosophila melanogaster/genética , Genes de Insetos , Proteínas de Insetos/genética , RNA Helicases/genética , Fatores de Transcrição/genética , Sequência de Aminoácidos , Animais , Anticorpos Monoclonais/imunologia , Núcleo Celular/ultraestrutura , Cromossomos/química , Clonagem Molecular , Dípteros/embriologia , Drosophila melanogaster/embriologia , Embrião não Mamífero/metabolismo , Embrião não Mamífero/ultraestrutura , Feminino , Técnica Indireta de Fluorescência para Anticorpo , Regulação da Expressão Gênica no Desenvolvimento , Proteínas de Insetos/imunologia , Proteínas de Insetos/fisiologia , Masculino , Dados de Sequência Molecular , RNA Helicases/imunologia , RNA Helicases/fisiologia , Alinhamento de Sequência , Homologia de Sequência de Aminoácidos , Processos de Determinação Sexual , Especificidade da Espécie , Fatores de Transcrição/imunologia , Fatores de Transcrição/fisiologia , Transcrição Gênica , Cromossomo X/genéticaRESUMO
The scute (sc) gene, a member of the achaete-scute complex of Drosophila melanogaster, has dual functions: sisterless (sis-b) function required for sex determination and dosage compensation and scute function, which is involved in neurogenesis. The sc homologue of D. subobscura was cloned. It lacks introns and encodes a single 1.7-kb transcript slightly larger than that of D. melanogaster (1.6 kb). The sc protein of D. subobscura is slightly larger than that of D. melanogaster (382 vs. 345 amino acids). Sequence comparisons between both species show the Sc protein to have a highly conserved bHLH domain. Outside this domain, amino acid replacements are not randomly distributed. Two additional conserved domains, of 20 and 36 amino acids, are present near the C-terminal end. They may represent domains confering specificity upon the Sc protein with respect to other proteins of the achaete-scute complex. In its 3' untranslated region, Sc RNA contains uridine stretches, putative Sxl protein DNA-binding sites. The D. subobscura Sc protein can cooperate with other D. melanogaster bHLH proteins because D. subobscura sc supplies sis-b function when introduced into D. melanogaster transgenic flies mutant for sc.
