Abstract:
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Communication n° 299. Myotubularin is a phosphoinositide phosphatase with an essential function in skeletal muscle. It is encoded by the MTM1 gene which, when mutated, leads to X-linked myotubular myopathy in humans and a progressive centronuclear myopathy in mice with early postnatal lethality in both species. MTM1 belongs to a large disease-associated gene family with 14 members in humans, MTMR2 and MTMR13 being implicated in Charcot-Marie-Tooth (CMT) demyelinating neuropathies type 4B1 and 4B2, respectively. Although MTM1 mRNA appears ubiquitously expressed, we show by quantitative RT-PCR that RNA level of MTM1 is higher than MTMR2 in muscle tissues but lower in brain and testis. In addition, all other MTM1 gene family members are also expressed in skeletal muscle. We have generated a novel rabbit polyclonal antibody against the C-terminal part of myotubularin that can detect the endogenous protein by direct immunoblotting and immunohistochemistry in various tissues. We show that myotubularin is ubiquitously expressed in adult mice, the levels being higher in striated muscles than in the central and peripheral nervous systems, probably explaining the tissue specificity of XLMTM versus CMT. Moreover, myotubularin expression is regulated during skeletal muscle development; in particular, the levels are low during mouse embryonic life and increase around postnatal day 7. Similarly, myotubularin level increases between gestation weeks 24 and 35 in human skeletal muscle. This indicates that myotubularin may play an important role during late muscle formation in both mouse and human. We have analysed the subcellular localisation of myotubularin in mouse skeletal muscle and heart at various ages and observed that it is distributed in a striated pattern. We are currently performing colocalisation studies with various myomarkers and determining precisely the location of myotubularin in muscles by immunoelectron microscopy. These results may provide important clues about the function of myotubularin in skeletal muscle.
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