Abstract:
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Centronuclear myopathies (CNM) are a group of congenital disorders characterized by hypotonia and typical skeletal muscle biopsies showing small rounded fibres with centralized nuclei. Three forms have been documented: the X-linked form with mutations in phosphoinositide (PI) phosphatase myotubularin (MTM1), an autosomal dominant form with mutations in dynamin 2 (DNM2) and our group has recently identified mutations in amphiphysin 2 / BIN1 in patients with autosomal recessive centronuclear myopathy, including two mutations leading to a premature stop codon. These mutations were previously shown to have an impact either on BIN1- dependent membrane tubulation or on interactions with partners as dynamin 2. The aim of our research is to better understand the role of amphyphysin2/BIN1 in healthy muscle and in the pathology of CNM. We are characterising constitutive (CMV) and muscle-specific (HSA) mice lines generated by targeted homologous recombination in ES cells, for exon 11 (muscle specific exon encoding for a PI-binding domain) and exon 20 (encoding a SH3 domain) of BIN1. The first deletion is expected to disrupt the regulation of BIN1 by phosphoinositides and thus potentially the link with MTM1. Deletion of exon 20 should disrupt the SH3 domain and potentially interfere with BIN1 protein interactions, including the interaction with its physical binding partner dynamin 2. The deletion of exon 20 deletion should mimic and behave similarly to the BIN1 premature stop codon mutations found in the CNM patients. Although CMVexon11 knockout (KO) mice seem relatively healthy and live as long as their heterozygous littermates, muscle biopsy analysis has revealed increased centralization of nuclei, which is one of the main features of CNM. We are currently performing behavioural studies and additional immunohistochemical analysis to characterize the CNM features observed further. Considering the total (CMV) KO of exon 20, it was perinatally lethal. The homozygote newborn mice are not grossly different from littermates and the cause of death is currently being investigated. Characterization of the first animal model for autosomal recessive CNM will give us a better comprehension of the pathological mechanisms leading to this disease.
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