Muscle and Muscle Connective Tissue Development in the Vertebrate Llmb

描述(申请人提供)：脊椎动物肌肉骨骼系统的发展需要肌肉、肌肉结缔组织、肌腱和骨骼的协调形态发生。在肢体中，肌肉来源于起源于体节的迁徙前体，而肌肉结缔组织、肌腱和骨骼元素来源于新出现的侧板起源的肢芽的中胚层。随着肌肉前体迁移到肢体，它们必须分化成肌纤维，正确地形成不同的解剖肌肉，并组装成一个有功能的肌肉骨骼。40多块四肢肌肉是如何形成图案的，肌肉和肌肉结缔组织的形态发生是如何协调的，这是本提案的主题。经典研究表明，侧板、四肢中胚层信号是肌肉重要的构图方式。然而，无论是信号的分子性质还是产生它的组织都不清楚。最近，我们发现了一群侧板，肢体中胚层细胞，表达转录因子TCF4，Wnt/β-catenin信号通路的下游效应因子，这对肌肉模式是至关重要的。对雏鸡的功能研究表明，表达TCF4的细胞在肢体中胚层建立了一个前模式，该模式决定了肌肉前体在哪里分化，从而决定了个别肌肉将在哪里形成，以及最终的肢体肌肉模式。此外，初步研究表明，表达TCF4的细胞是肌肉结缔组织的前体，肌肉结缔组织对肌肉骨骼的形式和功能至关重要，由于缺乏早期分子标记，其发育在很大程度上尚未被研究。我们建议在小鼠身上测试四肢中胚层表达TCF4的细胞和Wnt/β-catenin信号在确定四肢肌肉模式中的作用。此外，我们将确定表达TCF4的细胞是否是肌肉结缔组织形成所必需的前体。这些实验将为肌肉和肌肉结缔组织的正常发育以及Wnt/β-catenin信号在调节它们发育中的作用提供重要的见解。肌肉和肌肉结缔组织发育的中断可导致严重的肌肉-肌腱紊乱，如杜氏肌营养不良症和乌尔里希先天性肌营养不良症。我们的实验结果将使我们对这些疾病的病因学有重要的新见解。

DESCRIPTION (provided by applicant): Development of the vertebrate musculoskeletal system requires the coordinated morphogenesis of muscle, muscle connective tissue, tendon, and skeleton. In the limb, muscle derives from migratory precursors originating from the somites, while the muscle connective tissue, tendons and skeletal elements derive from the mesoderm of the emerging lateral-plate derived limb bud. As the muscle precursors migrate into the limb, they must differentiate into myofibers, become correctly patterned into distinct anataomical muscles, and be assemebled into a functional musculoskeleton. How the over 40 limb muscles are patterned and muscle and muscle connective tissue morphogenesis coordinated is the subject of this proposal. Classical studies had suggested that lateral plate, limb mesodermal signals are important patterning muscle. However, neither the molecular nature of the signal nor the tissue producing it was known. Recently we have identified a population of lateral plate, limb mesodermal cells that expresses the transcription factor Tcf4, a downstream effector of the Wnt/beta-catenin signaling pathway, and that is critical for muscle patterning. Functional studies in the chick suggest that Tcf4-expressing cells establish a prepattern in the limb mesoderm that determines where muscle precursors differentiate and thus where individual muscles will form and the ultimate limb muscle pattern. In addition, preliminary studies indicate that Tcf4-expressing cells are the precursors of the muscle connective tissue, a tissue of fundamental importance to the form and function of the musculoskeleton and whose development has been largely unstudied because of the lack of early molecular markers. We propose to test genetically in the mouse the role of limb mseodermal Tcf4- expressing cells and Wnt/beta-catenin signaling in determining the pattern of limb muscles. In addition, we will determine whether Tcf4-expressing cells are precursors necessary for formation of muscle connective tissue. These experiments will provide important insights into the normal development of muscle and muscle connective tissue and the role of Wnt/beta-catenin signaling in regulating their development. Disruptions in the development of muscle and muscle connective tissues can result in severe musculoskeltal disorders, such as Duchenne's muscular dystrophy and Ullrich congenital muscular dystrophy. Results from our experiments will give us important new insights into the etiology of these diseases.