Regulation of Extraocular Muscle Development

描述（由申请人提供）：骨骼肌并不都是平等的。肌前体细胞或成肌细胞不是一个具有预定命运的同质群体，而是代表来自各种胚胎来源的不同谱系。外部因素与谱系相互作用，塑造了发育中的肌纤维的分子/细胞/结构特征。眼外肌（EOMs）在骨骼肌中尤为独特。我们的中心假设是，新的EOM表型的发展依赖于细胞自主和非细胞自主的调节机制，这些机制与其他骨骼肌中决定成肌细胞命运的机制既相同又明显不同。具体来说，我们提出眼窝环境特有的神经相互作用和由组织特异性转录因子控制的信号级联直接表达EOM特异性、骨骼和心肌特征，使其适应眼动控制系统所需的广泛动态生理范围。一个核心问题是，来自“传统”肌肉研究的大量数据不足以解释独特EOM特性的模式和规范。我们最近的表达谱研究和EOM细胞系的发展为现在识别和直接测试EOM调节机制提供了知识和工具。特异性目标1将利用永生化EOM和后肢肌肉细胞系结合基因/蛋白表达谱，研究EOM发育过程中的细胞自主调节机制。特异性目标2将研究转录因子Pitx2在调节EOM发展的早期和晚期特征中的作用。Pitx2突变小鼠的等位基因系列将用于确定一般和纤维类型特异性性状调节的剂量依赖性。具体目标3将确定轨道环境特有的非细胞自主机制在形成EOM发展中的作用。我们发现，在器官型共培养中，EOM的存活依赖于动眼肌运动神经元的神经支配，通过评估正确运动神经元与不正确运动神经元培养中EOM的分子专一性，我们将扩大这一发现。该建议的健康相关性是，为了理解其独特的功能特征和对代谢和神经肌肉疾病的差异反应，明确需要了解EOM表型的分子特征。

DESCRIPTION (provided by applicant): Skeletal muscles are not all created equal. Muscle precursor cells or myoblasts are not a homogeneous population with a preordained fate, but rather represent distinct lineages derived from a variety of embryonic sources. Extrinsic factors interact with lineage in sculpting the molecular/cellular/structural traits of developing myofibers. The extraocular muscles (EOMs) are particularly unique among skeletal muscles. Our central hypothesis is that development of the novel EOM phenotype relies upon cell autonomous and non-cell autonomous regulatory mechanisms that are both shared with and strikingly divergent from those determining myoblast fates in other skeletal muscles. Specifically, we propose that neural interactions unique to the orbital environment and signaling cascades controlled by tissue-specific transcription factors direct EOM expression of a diverse array of EOM-specific, skeletal, and cardiac muscle traits that adapt it to the wide dynamic physiologic range required by eye movement control systems. A central problem is that the wealth of data from 'traditional' muscle studies is insufficient to explain the patterning and specification of distinctive EOM properties. Our recent expression profiling studies and development of an EOM cell line have provided the knowledge and tools to now identify and directly test EOM regulatory mechanisms. Specific Aim 1 will address cell autonomous regulatory mechanisms in EOM development, using immortialized EOM and hindlimb muscle cell lines in conjunction with gene/protein expression profiling. Specific Aim 2 will examine the role of the transcription factor, Pitx2, in regulating early and late features of EOM development. An allelic series of Pitx2 mutant mice will be used to determine dose dependence in regulation of both general and fiber type-specific traits. Specific Aim 3 will determine the role of a non-cell autonomous mechanism, unique to the orbital environment, in shaping EOM development. Our finding that EOM survival in organotypic co-culture is dependent upon oculomotor motoneuron innervation will be extended by assessing molecular specialization of EOM in culture with correct vs. incorrect motoneurons. The health relatedness of this proposal is that there is a clear need to understand the molecular specification of the EOM phenotype in order to comprehend both its unique functional features and differential responsiveness to metabolic and neuromuscular disease.