Regulation of Extraocular Muscle Development

描述(申请人提供)：骨骼肌并不都是生而平等的。肌肉前体细胞或成肌细胞并不是一个具有注定命运的同质群体，而是代表着来自各种胚胎来源的不同谱系。外在因素与谱系相互作用，塑造发育中的肌纤维的分子/细胞/结构特征。眼外肌(EOMS)在骨骼肌中特别独特。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调节机制，这些调节机制既与决定其他骨骼肌成肌细胞命运的机制相同，也与决定成肌细胞命运的机制显著不同。具体地说，我们认为，眼眶环境特有的神经相互作用和组织特异性转录因子控制的信号级联，指导了一系列EOM特异的、骨骼肌和心肌特征的EOM表达，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丰富数据不足以解释独特的EOM特性的模式和规格。我们最近的表达谱研究和EOM细胞系的开发为现在识别和直接测试EOM调节机制提供了知识和工具。具体目标1将探讨EOM发育中的细胞自主调节机制，使用永生化EOM和后肢肌肉细胞系，并结合基因/蛋白质表达谱。具体目标2将研究转录因子Pitx2在调节EOM发育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被用来确定一般和纤维类型特定性状的调节中的剂量依赖关系。具体目标3将确定轨道环境所特有的非细胞自主机制在影响EOM发育方面的作用。我们发现，EOM在器官型共培养中的存活依赖于动眼运动神经元的神经支配，这一发现将通过评估EOM在含有正确与错误运动神经元的培养中的分子专化性来延长。这一建议与健康相关的是，显然需要了解EOM表型的分子规范，以便理解其独特的功能特征以及对代谢和神经肌肉疾病的不同反应。

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.