Regulation of Tendon Induction and Formation By TGFbeta Signaling

描述（由申请人提供）：功能性肌肉骨骼系统依赖于从肌肉到骨骼的力传递，因此需要肌肉、软骨和肌腱的协调发展。然而，关于肌腱形成的细胞和分子方面所知甚少。揭示指示间充质细胞转变为腱细胞的信号的进展，对于阐明塑造肌肉骨骼系统组织和协调生长的早期事件具有特别重要的意义。此外，肌腱诱导活性对于改善肌腱损伤的治疗和诱导干细胞形成肌腱的生物工程努力可能具有相当大的临床重要性。最近发现，一种bHLH转录因子sccleraxis （Scx）是肌腱细胞和肌腱祖细胞的独特标记物，促进了对肌腱发育的研究，随后的许多研究表明FGF信号在肌腱祖细胞的诱导中起作用。我们实验室的戏剧性结果现在证明了TGF（信号传导）在肌腱诱导和分化中的更深远的作用。TGF(2和TGF(3基因双突变体的胚胎发育成四肢，但未检测到肌腱。此外，在器官培养和组织培养实验中，TGF信号作为Scx的有效诱导剂，在类似实验中显著超过FGF信号诱导Scx的程度和强度。我们拟通过三组实验探讨TGF（）在肌腱形成中的作用。第一个目标将解决所有肌腱组织都依赖于TGF（信号传导）的假设。轴肌腱和颅肌腱的表型将在TGF（2和3）突变体和TGF(受体TGF（RII）突变体中进行评估，其中所有TGF(信号都被消除。我们将进一步研究这些突变体肌腱表型的开始，以确定TGF（信号传导）在肌腱形成中所必需的阶段。第二个目的将是解决TGF信号对于肌腱形成的后期方面也是必不可少的假设。诱导消除TGF(RII将有助于探索TGF（）信号的后期作用，并确定肌腱是由一个固定的早期祖细胞池产生的，还是通过TGF（）信号持续募集肌腱细胞来支持肌腱生长。最后，我们将在组织培养和体内探索TGF（）信号诱导Scx的机制，比较TGF（）和FGF（）信号的活性，并结合特异性拮抗剂和突变组织探索这两个信号级联之间协同作用或相互依赖的可能性。此外，TGF（）将在子宫内使用逆转录病毒系统来评估TGF（）信号诱导的细胞超越Scx表达并导致异位或扩张肌腱形成的能力。

DESCRIPTION (provided by applicant): A functional musculoskeletal system depends upon the transmission of force from muscle to bone, thus requiring the coordinated development of muscle, cartilage and tendon. Little however, is known about the cellular and molecular aspects of tendon formation. Progress unraveling the signals that direct mesenchymal cells to become tenocytes is of particular importance in elucidation of the early events that shape the organization and coordinated growth of the musculoskeletal system. Moreover, a tendon inducing activity may be of considerable clinical importance both for improvements in the treatment of tendon injuries and in bioengineering efforts to induce tendon formation from stem cells. The recent finding that Scleraxis (Scx) a bHLH transcription factor is a unique marker of tenocytes and tendon progenitors facilitated studies of tendon development and a number of subsequent studies have implicated FGF signaling in the induction of tendon progenitors. Dramatic results in our laboratory now demonstrate an even more profound role for TGF( signaling in tendon induction and differentiation. Embryos doubly mutant for the TGF(2 and TGF(3 genes develop limbs in which no tendons can be detected. Moreover, TGF( signaling acts as a potent inducer of Scx, in organ culture and in tissue culture experiments, significantly exceeding the extent and intensity of Scx induction by FGF signaling in similar experiments. We propose to explore TGF( role in tendon formation in three separate groups of experiments. The first aim will address the hypothesis that all tendon tissues depend on TGF( signaling. The phenotype in axial and cranial tendons will be evaluated in TGF(2 & 3 mutants and in mutants for a TGF( receptor (TGF(RII), in which all TGF( signaling is eliminated. We will further study the onset of the tendon phenotype in these mutants to establish the stage in which TGF( signaling is essential for tendon formation. The second aim will be to address the hypothesis that TGF( signaling is essential for later aspects of tendon formation as well. Inducible elimination of TGF(RII will enable exploration of later roles for TGF( signaling and establish if tendons are generated from a committed pool of early progenitors or through continuous recruitment of tendon cells by TGF( signaling to support tendon growth. Finally, the mechanism of Scx induction by TGF( signaling will be explored in tissue culture and in vivo; the activities of TGF( and FGF signaling will be compared and the possibilities of synergism or interdependence between these two signaling cascades will be explored using a combination of specific antagonists and mutant tissues. In addition, TGF( will be applied in utero using a retroviral system to evaluate the capacity of the cells induced by TGF( signaling to go beyond expression of Scx and cause the formation of ectopic or expanded tendons.