The goal of this Project is to understand the molecular basis for X-linked myotubular myopathy (XLMTM) by determining the effects of myotubularin mutations on gene expression. Pathologically, XLMTM is characterized by incomplete muscle maturation caused by defects in myotubularin, a dual specificity protein phosphatase. This study entails the developmental characterization of global gene expression of known genes and novel expressed sequence tags (ESTs) in XLMTM and related disorders from the SP stem cell stage through to mature muscle. Understanding perturbations in gene expression will shed light on the function of myotubularin and its role in normal muscle development and may allow identification of therapeutic targets to stimulate normal muscle development in patients with XLMTM and related disorders of muscle development.

AIMS:

• To ascertain and characterize fresh muscle, muscle cell cultures and frozen muscle biopsies from patients with XLMTM and CTNM.
• To isolate and characterize muscle stem cells (SP cells) from myotubularin-deficient patients.
• To use chip-based mRNA expression arrays to analyze perturbations of gene expression associated with abnormalities of myotubularin in cultured muscle cells.
• To use chip-based mRNA expression arrays to analyze/compare XLMTM and CTNM human muscle to identify disease-specific and nonspecific changes in muscle gene expression.
• To validate results of expression arrays and characterize genes whose expression is specifically perturbed by myotubularin dysfunction.

Comparison of XLMTM-associated changes in gene expression with changes in CTNM and other congenital myopathies and dystrophies will allow identification of disease-specific changes. Correlation with data on various muscular dystrophies studied by other components of this Program Project will allow determination of non-dystrophic and dystrophy-specific pathogenic pathways. Knowledge of XLMTM-specific gene expression abnormalities will help in identifying downstream consequences of myotubularin dysfunction providing potential specific targets for therapeutic interventions to treat this disease. Furthermore, better knowledge of myotubularin’s role in muscle differentiation will help in identifying candidate genes for the milder related disease CTNM as well as shed light on normal muscle differentiation.