RESUMO
Adrenocortical dysplasia (acd) is a spontaneous autosomal recessive mouse mutation that exhibits a pleiotropic phenotype with perinatal lethality. Mutant acd embryos have caudal truncation, vertebral segmentation defects, hydronephrosis, and limb hypoplasia, resembling humans with Caudal Regression syndrome. Acd encodes Tpp1, a component of the shelterin complex that maintains telomere integrity, and consequently acd mutant mice have telomere dysfunction and genomic instability. While the association between genomic instability and cancer is well documented, the association between genomic instability and birth defects is unexplored. To determine the relationship between telomere dysfunction and embryonic malformations, we investigated mechanisms leading to the caudal dysgenesis phenotype of acd mutant embryos. We report that the caudal truncation is caused primarily by apoptosis, not altered cell proliferation. We show that the apoptosis and consequent skeletal malformations in acd mutants are dependent upon the p53 pathway by genetic rescue of the limb hypoplasia and vertebral anomalies with p53 null mice. Furthermore, rescue of the acd phenotype by p53 deficiency is a dosage-sensitive process, as acd/acd, p53(-/-) double mutants exhibit preaxial polydactyly. These findings demonstrate that caudal dysgenesis in acd embryos is secondary to p53-dependent apoptosis. Importantly, this study reinforces a significant link between genomic instability and birth defects.
Assuntos
Anormalidades Múltiplas/genética , Córtex Suprarrenal/anormalidades , Insuficiência Adrenal/genética , Apoptose/genética , Padronização Corporal/genética , Instabilidade Genômica/genética , Membro Posterior/anormalidades , Coluna Vertebral/anormalidades , Cauda/anormalidades , Telômero/patologia , Proteína Supressora de Tumor p53/fisiologia , Anormalidades Múltiplas/embriologia , Anormalidades Múltiplas/patologia , Córtex Suprarrenal/embriologia , Córtex Suprarrenal/patologia , Insuficiência Adrenal/embriologia , Insuficiência Adrenal/patologia , Animais , Cruzamentos Genéticos , Regulação da Expressão Gênica no Desenvolvimento , Genes Recessivos , Genes p53 , Idade Gestacional , Membro Posterior/embriologia , Membro Posterior/patologia , Camundongos , Camundongos Endogâmicos C57BL , Especificidade de Órgãos , Fenótipo , Complexo Shelterina , Coluna Vertebral/embriologia , Coluna Vertebral/patologia , Cauda/embriologia , Cauda/patologia , Proteínas de Ligação a Telômeros , Proteína Supressora de Tumor p53/deficiênciaRESUMO
OBJECTIVE: ACTH resistance is a feature of several human syndromes with known genetic causes, including familial glucocorticoid deficiency (types 1 and 2) and triple A syndrome. However, many patients with ACTH resistance lack an identifiable genetic aetiology. The human homolog of the Acd gene, mutated in a mouse model of adrenal insufficiency, was sequenced in 25 patients with a clinical diagnosis of familial glucocorticoid deficiency or triple A syndrome. DESIGN: A 3.4 kilobase genomic fragment containing the entire ACD gene was analysed for mutations in all 25 patients. SETTING: Samples were obtained by three investigators from different institutions. PATIENTS: The primary cohort consisted of 25 unrelated patients, primarily of European or Middle Eastern descent, with a clinical diagnosis of either familial glucocorticoid deficiency (FGD) or triple A syndrome. Patients lacked mutations in other genes known to cause ACTH resistance, including AAAS for patients diagnosed with triple A syndrome and MC2R and MRAP for patients diagnosed with familial glucocorticoid deficiency. Thirty-five additional patients with adrenal disease phenotypes were added to form an expanded cohort of 60 patients. MEASUREMENTS: Identification of DNA sequence changes in the ACD gene in the primary cohort and analysis of putative ACD haplotypes in the expanded cohort. RESULTS: No disease-causing mutations were found, but several novel single nucleotide polymorphisms (SNPs) and two putative haplotypes were identified. The overall frequency of SNPs in ACD is low compared to other gene families. CONCLUSIONS: No mutations were identified in ACD in this collection of patients with ACTH resistance phenotypes. However, the newly identified SNPs in ACD should be more closely examined for possible links to disease.
Assuntos
Hormônio Adrenocorticotrópico/metabolismo , Erros Inatos do Metabolismo/genética , Polimorfismo Genético , Proteínas de Ligação a Telômeros/genética , Insuficiência Adrenal/genética , Sequência de Bases , Pré-Escolar , Análise Mutacional de DNA , Acalasia Esofágica/genética , Feminino , Glucocorticoides/deficiência , Haplótipos , Humanos , Lactente , Recém-Nascido , Masculino , Erros Inatos do Metabolismo/metabolismo , Dados de Sequência Molecular , Polimorfismo de Nucleotídeo Único , Complexo Shelterina , SíndromeRESUMO
The spontaneous mouse mutant adrenocortical dysplasia (acd) is characterized by defects in the adrenals, kidneys, and gonads of adult mutant mice and by caudal dysgenesis and vertebral segmentation defects in acd embryos. This association of defects mirrors those identified in patients with known or suspected abnormalities in adrenocortical development, including adrenal hypoplasia congenita and IMAGe association. The identification of the Acd gene in mice has prompted the study of its human homolog ACD, which has recently been shown to be a regulator of telomere length. Sequencing of ACD in 15 patients revealed no coding mutations, but three novel SNPs were identified.
