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Updated: May 17, 2026
Modeling Myotonic Dystrophy 1 in C2C12 Myoblast Cells
Published on: July 29, 2016
Phosphatase-dead myotubularin ameliorates X-linked centronuclear myopathy phenotypes in mice
Leonela Amoasii1, Dimitri L Bertazzi, Hélène Tronchère
1Department of Translational Medecine, Institut de Génétique et de Biologie Moléculaire et Cellulaire (IGBMC), INSERM U964, CNRS UMR7104, Université de Strasbourg, Collège de France, Illkirch, France.
Abstract:
Myotubularin MTM1 is a phosphoinositide (PPIn) 3-phosphatase mutated in X-linked centronuclear myopathy (XLCNM; myotubular myopathy). We investigated the involvement of MTM1 enzymatic activity on XLCNM phenotypes. Exogenous expression of human MTM1 in yeast resulted in vacuolar enlargement, as a consequence of its phosphatase activity. Expression of mutants from patients with different clinical progression and determination of PtdIns3P and PtdIns5P cellular levels confirmed the link between vacuolar morphology and MTM1 phosphatase activity, and showed that some disease mutants retain phosphatase activity. Viral gene transfer of phosphatase-dead myotubularin mutants (MTM1(C375S) and MTM1(S376N)) significantly improved most histological signs of XLCNM displayed by a Mtm1-null mouse, at similar levels as wild-type MTM1. Moreover, the MTM1(C375S) mutant improved muscle performance and restored the localization of nuclei, triad alignment, and the desmin intermediate filament network, while it did not normalize PtdIns3P levels, supporting phosphatase-independent roles of MTM1 in maintaining normal muscle performance and organelle positioning in skeletal muscle. Among the different XLCNM signs investigated, we identified only triad shape and fiber size distribution as being partially dependent on MTM1 phosphatase activity. In conclusion, this work uncovers MTM1 roles in the structural organization of muscle fibers that are independent of its enzymatic activity. This underlines that removal of enzymes should be used with care to conclude on the physiological importance of their activity.
Insights
Myotubularin (MTM1) enzyme activity is not solely responsible for X-linked centronuclear myopathy (XLCNM) phenotypes. This study reveals MTM1 has structural roles in muscle fibers independent of its enzymatic function, impacting disease progression.
Area of Science:
- Cell Biology
- Biochemistry
- Genetics
Background:
- X-linked centronuclear myopathy (XLCNM) is a severe congenital muscle disorder caused by mutations in the myotubularin (MTM1) gene.
- MTM1 is a phosphoinositide 3-phosphatase, and its enzymatic activity has been presumed to be the primary driver of XLCNM pathology.
Purpose of the Study:
- To investigate the specific contribution of MTM1's enzymatic activity to XLCNM phenotypes.
- To differentiate between the phosphatase-dependent and -independent functions of MTM1 in skeletal muscle.
Main Methods:
- Exogenous expression of wild-type and mutant MTM1 in yeast and Mtm1-null mouse models.
- Analysis of phosphoinositide levels (PtdIns3P and PtdIns5P) and various histological and functional parameters in muscle tissues.
- Viral gene transfer of catalytically inactive MTM1 mutants.
Main Results:
- MTM1 phosphatase activity is linked to vacuolar morphology in yeast and XLCNM models.
- Catalytically dead MTM1 mutants significantly improved XLCNM histological signs and muscle performance in mice.
- These improvements occurred independently of PtdIns3P normalization, highlighting phosphatase-independent roles in muscle structure and function.
- Only triad shape and fiber size distribution were partially dependent on MTM1 phosphatase activity.
Conclusions:
- MTM1 plays crucial roles in the structural organization of muscle fibers that are independent of its enzymatic phosphatase activity.
- Therapeutic strategies targeting XLCNM should consider both enzymatic and structural functions of MTM1.
- The physiological importance of enzyme activity should be carefully evaluated, as non-enzymatic functions can be critical.
