RESUMO
Spinal muscular atrophy (SMA) is characterized by degeneration of motor neurons of the spinal cord associated with muscle paralysis and caused by mutations of the survival motor neuron gene (SMN). To determine whether SMN gene defect in skeletal muscle might have a role in SMA pathogenesis, deletion of murine SMN exon 7, the most frequent mutation found in SMA, has been restricted to skeletal muscle by using the Cre-loxP system. Mutant mice display ongoing muscle necrosis with a dystrophic phenotype leading to muscle paralysis and death. The dystrophic phenotype is associated with elevated levels of creatine kinase activity, Evans blue dye uptake into muscle fibers, reduced amount of dystrophin and upregulation of utrophin expression suggesting a destabilization of the sarcolemma components. The mutant mice will be a valuable model for elucidating the underlying mechanism. Moreover, our results suggest a primary involvement of skeletal muscle in human SMA, which may contribute to motor defect in addition to muscle denervation caused by the motor neuron degeneration. These data may have important implications for the development of therapeutic strategies in SMA.
Assuntos
Éxons/genética , Músculo Esquelético/metabolismo , Músculo Esquelético/patologia , Atrofia Muscular Espinal/genética , Distrofias Musculares/patologia , Proteínas do Tecido Nervoso/genética , Deleção de Sequência/genética , Animais , Biomarcadores , Tamanho Celular , Creatina Quinase/metabolismo , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico , Proteínas do Citoesqueleto/metabolismo , Distrofina/metabolismo , Azul Evans/metabolismo , Imunofluorescência , Proteínas de Membrana/metabolismo , Camundongos , Neurônios Motores/metabolismo , Neurônios Motores/patologia , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/patologia , Distrofias Musculares/enzimologia , Distrofias Musculares/metabolismo , Junção Neuromuscular/metabolismo , Proteínas de Ligação a RNA , Proteínas do Complexo SMN , Sarcolema/metabolismo , Sarcolema/patologia , UtrofinaRESUMO
Deletion of the murine survival of motor neuron gene (SMN) exon 7, the most frequent mutation found in spinal muscular atrophy (SMA) patients, directed to neurons but not to skeletal muscle, enabled generation of a mouse model of SMA providing evidence that motor neurons are the primary target of the gene defect. Moreover, the mutated SMN protein (SMNDeltaC15) is dramatically reduced in the motor neuron nuclei and causes a lack of gems associated with large aggregates of coilin, a coiled-body-specific protein. These results identify the lack of the nuclear targeting of SMN as the biochemical defect in SMA.
Assuntos
Núcleo Celular/metabolismo , Atrofia Muscular Espinal/genética , Proteínas do Tecido Nervoso/genética , Animais , Sequência de Bases , Proteína de Ligação ao Elemento de Resposta ao AMP Cíclico , Primers do DNA , Modelos Animais de Doenças , Éxons , Deleção de Genes , Genes Letais , Homozigoto , Camundongos , Neurônios Motores/metabolismo , Atrofia Muscular Espinal/metabolismo , Proteínas do Tecido Nervoso/química , Fenótipo , Proteínas de Ligação a RNA , Proteínas do Complexo SMNRESUMO
Spatially and temporally regulated somatic mutations can be achieved by using the Cre/LoxP recombination system of bacteriophage P1. In order to develop gene knockouts restricted to striated muscle, we generated a transgenic mouse line expressing Cre recombinase under the control of the human alpha-skeletal actin promoter. Specific excision of a loxP-flanked gene was demonstrated in striated muscle, heart and skeletal muscle, in a pattern very similar to the expression of the endogenous alpha-skeletal actin gene. Therefore, the reported transgenic line can be used to target inactivation or activation of a given gene to the skeletal muscle lineage.
