SPEG is Critical in Skeletal Muscle Development and Function

描述（由申请人提供）：先天性肌病（CM）是一种异质性骨骼肌疾病，在生命早期表现为张力低下、呼吸和进食困难，通常是致命的。中核性肌病（CNM）是一种常见的CM亚型，其特征是细胞核从周围到肌纤维中心的错误定位。x连锁肌小管肌病是CNM最常见和最严重的形式，由MTM1突变引起。肌管蛋白（MTM1）是一种脂质磷酸酶，对其相互作用的伙伴知之甚少。为了确定与mtm1相互作用的蛋白，我们进行了酵母双杂交筛选，发现条纹优先表达基因（striated preferred expression gene， SPEG）是相互作用的伙伴。同时，为确定CNM的遗传基础而进行的全外显子组测序显示，来自三个不相关CNM家族的先显子存在隐性SPEG突变。三人中的两人也被诊断为扩张型心肌病（DCM），其中一人在一年内自然消退。我们的研究结果表明，SPEG突变导致CNM表型，但骨骼肌功能障碍的潜在基础尚不清楚。在小鼠模型中，敲除Speg与严重的DCM、中央核数量增加和出生后第2天死亡有关。SPEG和desmin基因在基因组上串联排列，在哺乳动物中有一个共同的基因座控制区调节它们的表达。免疫荧光研究表明，SPEG定位于肌浆网（SR）的末端池。我们认为SPEG可以维持终端SR结构以实现有效的激励-收缩耦合。在Aim 1中，我们将破译与SPEG缺乏相关的骨骼肌功能差的分子机制及其在骨骼肌和心肌中的不同作用。在Aim 2中，我们将研究SPEG在骨骼肌生长和分化中的作用，特别关注中央成核。在Aim 3中，我们将确定SPEG、MTM1和desmin之间的关系。该提案的总体目标是了解SPEG缺乏如何影响肌肉功能，其在肌肉生长和分化中的作用，以及与MTM1和desmin的关系。一旦完成，这项工作将为骨骼肌中SPEG的分子功能以及其缺乏如何导致CNM提供清晰的见解。这些发现将有助于确定针对这种毁灭性肌肉疾病的治疗方法。

DESCRIPTION (provided by applicant): Congenital myopathies (CM) are a heterogeneous group of skeletal muscle disorders that manifest as hypotonia as well as breathing and feeding difficulties early in life, and can often be fatal. Centronuclear myopathy (CNM) is a common CM subtype characterized by the mislocalization of nuclei from the periphery to the center of myofibers. X-linked myotubular myopathy, the most frequent and severe form of CNM, is caused by MTM1 mutations. Myotubularin or MTM1 is a lipid phosphatase, and little is known about its interacting partners. To determine MTM1-interacting proteins, we conducted a yeast two-hybrid screen and found striated preferentially expressed gene (SPEG) to be an interacting partner. Concurrently, whole exome sequencing to determine genetic basis of CNM revealed recessive SPEG mutations in probands from three unrelated CNM families. Two of the three were also diagnosed with dilated cardiomyopathy (DCM), one of which had spontaneous resolution by a year. Our results suggest that mutations in SPEG cause a CNM phenotype, but the underlying basis for skeletal muscle dysfunction is unknown. Knocking out Speg in a mouse model has been associated with severe DCM, an increased number of central nuclei, and death by postnatal day two. SPEG and desmin genes are tandemly arrayed on the genome, and a common locus control region in mammals regulates their expression. Immunofluorescence studies have shown that SPEG localizes with the terminal cisternae of the sarcoplasmic reticulum (SR). We propose that SPEG may maintain terminal SR structure for efficient excitation-contraction coupling. In Aim 1, we will decipher the molecular mechanisms responsible for poor skeletal muscle function associated with lack of SPEG and its differential role in skeletal and cardiac muscles. In Aim 2, we will investigate SPEG's involvement in skeletal muscle growth and differentiation, with special focus on central nucleation. In Aim 3, we will determine the relationship between SPEG, MTM1, and desmin. The overall goals of the proposal are to understand how lack of SPEG affects muscle function, its role in muscle growth and differentiation, and relationship with MTM1 and desmin. When completed, this work will provide clear insights into the molecular functions of SPEG in skeletal muscle, and how its deficiency causes CNM. The findings will help determine therapeutic approaches against such devastating muscle diseases.