The Role of CDO in Myogenic Differentiation

描述(申请人提供)：骨骼肌前体的指定和分化由MyoD转录因子家族控制，该家族与额外的转录因子合作，协调肌肉特异性基因的表达，并融合成多核肌纤维。有几个信号通路调节这些因子的活性并促进肌肉生成，但启动这些通路的细胞表面蛋白还不是很清楚。CDO是一种表达在肌肉前体细胞上的孤儿细胞表面受体。缺乏CDO的小鼠表现出骨骼肌发育迟缓，CDO在体外促进肌源性分化。CDO是在细胞-细胞接触部位发现的复合体的一个组成部分，其中包含几种促肌原蛋白，包括密切相关的受体BOC；细胞黏附分子N-和M-钙粘附素；以及网织蛋白受体新生素。CDO信号通过增强的异二聚化来激活MyoD，可能是通过诱导其E蛋白伙伴的过度磷酸化来激活MyoD，而钙粘附素和netrin/negenin信号则激活其他途径。这种复杂的成分在它们的某些活动中表现出相互依赖的关系(即CDO需要钙粘附素，BOC和新生素需要CDO)。假设细胞-细胞接触部位的多蛋白复合体允许不同的信号事件在分化过程中协调调节形态和转录反应。提出了一种多学科的方法，总体目标是获得含有CDO的复合体如何调节骨骼肌发育的机制观点。其具体目的是：1)确定CDO结合伙伴BOC和新生素在活体肌肉发生中的作用；2)分析含CDO的细胞表面复合体的生化和信号特性；3)分析CDO介导的E蛋白过度磷酸化。这项研究应该有助于阐明骨骼肌发育的基本过程，从而为改进骨骼肌疾病的治疗提供潜在的策略。

DESCRIPTION (provided by applicant): Specification and differentiation of skeletal muscle precursors is controlled by the MyoD family of transcription factors, which cooperate with additional transcription factors to coordinate expression of muscle-specific genes and fusion into multinucleated myofibers. Several signaling pathways regulate the activity of these factors and promote myogenesis, but the cell surface proteins that initiate such pathways are not well understood. CDO is an orphan cell surface receptor expressed on muscle precursors. Mice lacking CDO display delayed skeletal muscle development, and CDO promotes myogenic differentiation in vitro. CDO functions as a component of a complex found at sites of cell-cell contact that contains several promyogenic proteins, including the closely related receptor, BOC; the cell adhesion molecules, N- and M-cadherin; and the netrin receptor, neogenin. CDO signals to activate MyoD via enhanced heterodimerization, likely by inducing hyperphosphorylation of its E protein partners, while cadherins and netrin/ neogenin signal to activate additional pathways. The components of this complex display interdependence in some of their activities (i.e., CDO requires cadherins, and BOC and neogenin require CDO). It is hypothesized that a multiprotein complex at sites of cell-cell contact permits diverse signaling events that regulate both morphological and transcriptional responses to be coordinated during differentiation. A multidisciplin- ary approach is proposed with the overall goal of gaining a mechanistic view of how CDO-containing complexes regulate skeletal muscle development. The Specific Aims are: 1) to identify the roles of the CDO binding partners, BOC and neogenin, in myogenesis in vivo; 2) to analyze biochemical and signaling properties of CDO-containing cell surface complexes; and 3) to analyze CDO-mediated hyperphosphorylation of E proteins. This research should shed light on fundamental processes by which skeletal muscles develop and therefore advance potential strategies for improved treatment of skeletal muscle diseases.