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  • Title: SPEG interacts with myotubularin, and its deficiency causes centronuclear myopathy with dilated cardiomyopathy.
    Author: Agrawal PB, Pierson CR, Joshi M, Liu X, Ravenscroft G, Moghadaszadeh B, Talabere T, Viola M, Swanson LC, Haliloğlu G, Talim B, Yau KS, Allcock RJ, Laing NG, Perrella MA, Beggs AH.
    Journal: Am J Hum Genet; 2014 Aug 07; 95(2):218-26. PubMed ID: 25087613.
    Abstract:
    Centronuclear myopathies (CNMs) are characterized by muscle weakness and increased numbers of central nuclei within myofibers. X-linked myotubular myopathy, the most common severe form of CNM, is caused by mutations in MTM1, encoding myotubularin (MTM1), a lipid phosphatase. To increase our understanding of MTM1 function, we conducted a yeast two-hybrid screen to identify MTM1-interacting proteins. Striated muscle preferentially expressed protein kinase (SPEG), the product of SPEG complex locus (SPEG), was identified as an MTM1-interacting protein, confirmed by immunoprecipitation and immunofluorescence studies. SPEG knockout has been previously associated with severe dilated cardiomyopathy in a mouse model. Using whole-exome sequencing, we identified three unrelated CNM-affected probands, including two with documented dilated cardiomyopathy, carrying homozygous or compound-heterozygous SPEG mutations. SPEG was markedly reduced or absent in two individuals whose muscle was available for immunofluorescence and immunoblot studies. Examination of muscle samples from Speg-knockout mice revealed an increased frequency of central nuclei, as seen in human subjects. SPEG localizes in a double line, flanking desmin over the Z lines, and is apparently in alignment with the terminal cisternae of the sarcoplasmic reticulum. Examination of human and murine MTM1-deficient muscles revealed similar abnormalities in staining patterns for both desmin and SPEG. Our results suggest that mutations in SPEG, encoding SPEG, cause a CNM phenotype as a result of its interaction with MTM1. SPEG is present in cardiac muscle, where it plays a critical role; therefore, individuals with SPEG mutations additionally present with dilated cardiomyopathy.
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