The functional role of sarcomeric nonmuscle myosin IIB in extraocular muscles

描述（由申请人提供）：眼外肌（EOMs）被归类为骨骼肌；然而，新出现的证据表明，它们明显偏离了这类肌肉的原型成员。例如，许多肌丝、细胞骨架和细胞外基质蛋白在发育和成年EOMs中具有独特的表达模式，包括胚胎和胎儿肌球蛋白亚型（MyHC）的持续表达，eom特异性MyHC的存在，以及心脏和骨骼肌粗丝和细丝附属蛋白亚型的共同表达。我们证明非肌球蛋白（nmMyH IIB）存在于推定的强直性EOM纤维的肌聚体a带中。虽然在心脏和骨骼肌的z线上发现了少量的nmMyH IIB，但其在EOM强直纤维A带内的独特分布进一步证明了眼肌的复杂性和非常规发育程序。我们将使用基因工程小鼠以组织和时间特异性的方式删除nmMyH IIB，以验证以下中心假设：nmMyH IIB在EOM纤维中的肌肉分布取决于出生后的正常视觉体验，并且是成年人正常EOM收缩功能所必需的。因此，我们确定了以下具体目的：1)确定nmMyH IIB在啮齿动物eom中的表达和肉瘤定位是否需要生命早期正常的视觉体验；2)确定nmMyH IIB对啮齿动物eom中肉瘤结构的作用；3)确定nmMyH IIB对啮齿动物eom收缩功能的影响。这些结果将确定nmMyH IIB在出生后早期发育和成人中EOM纤维中的作用，并为我们理解正常EOM表型及其如何随疾病变化提供有价值的见解。

DESCRIPTION (provided by applicant): The extraocular muscles (EOMs) are categorized as skeletal muscles; however, emerging evidence indicates that they deviate significantly from the prototypical members of this muscle class. For example, many myofilament, cytoskeletal and extracellular matrix proteins have unique expression patterns in developing and adult EOMs, including the sustained expression of embryonic and fetal myosin isoforms (MyHC), the presence of a unique EOM-specific MyHC, and co-expression of cardiac and skeletal muscle isoforms of thick and thin filament accessory proteins. We demonstrated that a nonmuscle myosin (nmMyH IIB) is present in the sarcomeric A band of putative tonic EOM fibers. Although small amounts of nmMyH IIB are found in the Z-line of cardiac and skeletal muscles, its unique distribution within the A band in EOM tonic fibers is further evidence of the complexity and unconventional developmental program of the eye muscles. We will use genetically engineered mice to delete nmMyH IIB in a tissue and time-specific manner in order to test the following central hypothesis: the sarcomeric distribution of nmMyH IIB in EOM fibers depends on normal visual experience postnatally and is necessary for normal EOM contractile function in the adult. Thus we have defined the following specific aims: 1) determine whether normal visual experience early in life is necessary for the expression and sarcomeric localization of nmMyH IIB in rodent EOMs, 2) define the role of nmMyH IIB on sarcomeric structure in rodent EOMs and 3) determine the influence of nmMyH IIB on the contractile function of rodent EOMs. These results will establish the role of nmMyH IIB in EOM fibers during early postnatal development and in the adult and should provide valuable insights into our understanding of the normal EOM phenotype and how it might change with disease.) PUBLIC HEALTH RELEVANCE: In addition to the sensory pathways, the ability to direct the eyes to items of interest is also key for normal vision. The extraocular muscles are the small muscles responsible for coordinated eye movements. This project will examine the function of a structural protein found in a unique position only in the extraocular muscles and that may be important for normal eye movements.)