RESUMO
A heteroplasmic T to C transition at nucleotide position 14709 in the mitochondrial tRNA glutamic acid (tRNA(Glu)) gene has previously been associated with maternally inherited diabetes and deafness (MIDD). To investigate the pathogenic mechanism of the T14709C mutation, we have constructed transmitochondrial cell lines by transferring fibroblasts mitochondria from a patient with the mutation into human cells lacking mitochondrial DNA (mtDNA) (rho degrees cells). Clonal cybrid cell lines were obtained containing various levels of the heteroplasmic mutation, or exclusively mutated or wild-type mtDNA. Measurement of respiratory chain enzymatic activities failed to detect a difference between the homoplasmic mutant and homoplasmic wild-type cybrid cell lines. However, a subtle decrease in the steady-state levels of tRNA(Glu) transcripts in some mutant clones. Our studies suggest that the T14709C mutation is insufficient to lead impairment of mitochondrial function in homoplasmic osteosarcoma cybrid clones, and that we cannot exclude that the T14709C mutation affects mitochondrial function by a yet unidentified mechanism.
Assuntos
DNA Mitocondrial/genética , Surdez/genética , Diabetes Mellitus/genética , Sequência de Bases , Northern Blotting , Fusão Celular , Células Clonais , Surdez/complicações , Complicações do Diabetes , Complexo I de Transporte de Elétrons , Complexo II de Transporte de Elétrons , Complexo III da Cadeia de Transporte de Elétrons/metabolismo , Fibroblastos/metabolismo , Genótipo , Humanos , Complexos Multienzimáticos/metabolismo , NADH NADPH Oxirredutases/metabolismo , Oxirredutases/metabolismo , Mutação Puntual , RNA de Transferência de Ácido Glutâmico/análise , Succinato Desidrogenase/metabolismoRESUMO
The Escherichia coli MutHLS system has been highly conserved throughout evolution. The eukaryotic pathway results in a specialization of MutS homologs that have evolved to play crucial roles in both DNA mismatch repair and meiotic recombination. So far, meiosis-specific genes belonging to this family have only been identified in yeast. In Saccharomyces cerevisiae, MSH4 (MutS homolog 4) is a meiosis-specific protein that is not involved in mismatch correction. This protein is required for reciprocal recombination and proper segregation of homologous chromosomes at meiosis I. We have identified the human MSH4 homolog gene. The predicted amino acid sequence shows 28.7% identity with the S. cerevisiae MSH4 protein. By Northern blot analysis, human MSH4 transcripts are only detectable in testis and in ovary with a lower level of expression. We have mapped MSH4 to human chromosome 1 at band p31 by fluorescence in situ hybridization. The identification of such a gene provides a powerful tool for clarifying the respective roles of MSH and MLH genes in mammalian meiosis.
Assuntos
Adenosina Trifosfatases , Proteínas de Bactérias/genética , Proteínas de Ciclo Celular/genética , Proteínas de Ligação a DNA , Proteínas de Escherichia coli , Meiose/genética , Proteínas de Saccharomyces cerevisiae , Sequência de Aminoácidos , Sequência de Bases , Mapeamento Cromossômico , Cromossomos Humanos Par 1/genética , Clonagem Molecular , Primers do DNA/genética , DNA Complementar/genética , Escherichia coli/genética , Evolução Molecular , Feminino , Proteínas Fúngicas/genética , Expressão Gênica , Humanos , Hibridização in Situ Fluorescente , Masculino , Dados de Sequência Molecular , Proteína MutS de Ligação de DNA com Erro de Pareamento , Saccharomyces cerevisiae/genéticaRESUMO
UNLABELLED: We studied a 3-month-old girl who was admitted to hospital because of respiratory distress. The clinical course was characterized by a rapidly progressive generalized hypotonia with lactic acidosis and she died at 4 months of age. A muscle biopsy showed few ragged-red fibres and lack of histochemical cytochrome c oxidase reaction in all fibres. Enzyme activities of the respiratory chain complexes containing subunits encoded by the mitochondrial DNA (mtDNA) were markedly decreased. A quantitative Southern blot analysis revealed 99% depletion of mtDNA in muscle and normal amounts in blood. There was no family history and the dizygotic twin sister of the patient was no symptomatic. CONCLUSION: This new case confirms the rapidly fatal evolution associated with severe depletion of muscle mtDNA.
Assuntos
DNA Mitocondrial/genética , Encefalomiopatias Mitocondriais/genética , Acidose Láctica/genética , Acidose Láctica/patologia , Encéfalo/patologia , Deficiência de Citocromo-c Oxidase , Doenças em Gêmeos/genética , Evolução Fatal , Feminino , Humanos , Lactente , Microscopia Eletrônica , Encefalomiopatias Mitocondriais/patologia , Hipotonia Muscular/genética , Hipotonia Muscular/patologia , Músculo Esquelético/patologia , Gêmeos DizigóticosRESUMO
The observation of two new cases in a previously reported family has brought about a change in the delineation of the syndrome initially defined. To the abnormalities already described (branchial dysplasia, mental deficiency, club feet, inguinal herniae) must be added a paucity of interlobular bile duts; the relationship between this new syndrome and the Alagille syndrome requires reconsideration.
Assuntos
Atresia Biliar/genética , Deformidades Congênitas do Pé/genética , Hérnia Inguinal/genética , Atresia Biliar/complicações , Deformidades Congênitas do Pé/complicações , Genes Recessivos , Hérnia Inguinal/complicações , Humanos , Lactente , Deficiência Intelectual , Masculino , SíndromeRESUMO
Two new familial cases of Winchester syndrome with the characteristic features allowed to be more explicit on a few data of this syndrome. As reported in a previous paper an abnormal oligosaccharide was detected in urine of patients but the pathological significance of this oligosaccharide must be discussed and its finding in patients with Winchester syndrome does not lead to further elucidation of the aetiology of this condition. Cultured fibroblasts were obtained from a skin biopsy performed in thickened area. These cells had a normal level of the hydrolases studied whereas they showed ultrastructural abnormalities with numerous secondary lysosomes and pseudomyelinic figures.