RESUMO
In the XX/XY sex-determining system, the Y-linked SRY genes of most mammals and the DMY/Dmrt1bY genes of the teleost fish medaka have been characterized as sex-determining genes that trigger formation of the testis. However, the molecular mechanism of the ZZ/ZW-type system in vertebrates, including the clawed frog Xenopus laevis, is unknown. Here, we isolated an X. laevis female genome-specific DM-domain gene, DM-W, and obtained molecular evidence of a W-chromosome in this species. The DNA-binding domain of DM-W showed a strikingly high identity (89%) with that of DMRT1, but it had no significant sequence similarity with the transactivation domain of DMRT1. In nonmammalian vertebrates, DMRT1 expression is connected to testis formation. We found DMRT1 or DM-W to be expressed exclusively in the primordial gonads of both ZZ and ZW or ZW tadpoles, respectively. Although DMRT1 showed continued expression after sex determination, DM-W was expressed transiently during sex determination. Interestingly, DM-W mRNA was more abundant than DMRT1 mRNA in the primordial gonads of ZW tadpoles early in sex determination. To assess the role of DM-W, we produced transgenic tadpoles carrying a DM-W expression vector driven by approximately 3 kb of the 5'-flanking sequence of DM-W or by the cytomegalovirus promoter. Importantly, some developing gonads of ZZ transgenic tadpoles showed ovarian cavities and primary oocytes with both drivers, suggesting that DM-W is crucial for primary ovary formation. Taken together, these results suggest that DM-W is a likely sex (ovary)-determining gene in X. laevis.
Assuntos
Proteínas de Ligação a DNA/genética , Proteínas de Drosophila/genética , Cromossomos Sexuais/genética , Fatores de Transcrição/genética , Xenopus laevis/crescimento & desenvolvimento , Xenopus laevis/genética , Animais , Proteínas de Ligação a DNA/metabolismo , Proteínas de Drosophila/metabolismo , Feminino , Regulação da Expressão Gênica no Desenvolvimento , Genoma/genética , Genótipo , Larva/genética , Larva/crescimento & desenvolvimento , Larva/metabolismo , Masculino , Dados de Sequência Molecular , Ovário , Regiões Promotoras Genéticas , Processos de Determinação Sexual , Fatores de Transcrição/metabolismo , Xenopus laevis/metabolismoRESUMO
Xylanase J (XynJ) from alkaliphilic Bacillus sp. 41M-1 is an alkaline xylanase. The crystal structure has been solved with XynJ. Improvement of the alkaliphily of XynJ was attempted by amino acid substitutions. Reinforcing the characteristic salt bridge in the catalytic cleft and introducing excess Arg residues on the protein surface shifted the optimum pH of the wild-type enzyme from 8.5 to 9.5.
Assuntos
Substituição de Aminoácidos , Bacillus/enzimologia , Domínio Catalítico , Endo-1,4-beta-Xilanases/química , Endo-1,4-beta-Xilanases/genética , Endo-1,4-beta-Xilanases/metabolismo , Engenharia de Proteínas/métodos , Concentração de Íons de Hidrogênio , Modelos Moleculares , Mutação , TemperaturaRESUMO
Xylanase J (XynJ) from alkaliphilic Bacillussp. strain 41M-1 is an alkaline xylanase. Structure comparison indicated that there were several specific salt bridges in the catalytic cleft of XynJ compared with neutral xylanases. Mutant enzymes were prepared by substituting several amino acids comprising the salt bridges. Some mutants exhibited acidophilic shift in optimum pH, whereas another showed alkaliphilic shift. These results suggested that the characteristic salt bridges could contribute to the alkaliphily of XynJ.
Assuntos
Bacillus/enzimologia , Proteínas de Bactérias/química , Endo-1,4-beta-Xilanases/química , Proteínas de Bactérias/genética , Endo-1,4-beta-Xilanases/genética , Concentração de Íons de Hidrogênio , Mutagênese Sítio-Dirigida , Sais/químicaRESUMO
The doublesex and mab-3-related transcription factor 1 (DMRT1) is involved in testis formation in a variety of vertebrates. In the teleost fish, Medaka, DMY/DMRT1Y on the Y chromosome, a duplicate of the autosomal DMRT1 gene, is characterized as a sex-determining gene. We report here the characterization of the Xenopus DMRT1 genes. Reverse transcription-polymerase chain reaction (RT-PCR) analysis revealed that X. laevis DMRT1 was expressed throughout the embryo during early development and was restricted to the primordial gonads after embryogenesis. Whole-mount in situ hybridization analysis of the gene confirmed its specific expression in the primordial gonads. To study the transcriptional control of DMRT1 gene expression, we isolated the predicted promoter region of X. tropicalis DMRT1 using databases for this species. Analysis of transgenic tadpoles with a green fluorescence protein (GFP) reporter showed that approximately 3 kb of the 5'-flanking sequence of the DMRT1 gene was implicated in DMRT1 expression in the primordial gonads. We also showed that the C-terminal region of DMRT1 functioned as a transactivation domain in cultured cells, by a luciferase reporter assay using fusion proteins with the DNA-binding domain of GAL4. These findings suggest that DMRT1 functions as an activator of one or more genes involved in sex determination or gonadal differentiation.