Role of Transcription Factor ERG in Skeletogenesis

描述（由申请人提供）：在肢体骨骼发生过程中，软骨细胞遵循两条发育路径，并产生终身持续的永久性关节软骨或暂时性生长板软骨，其中细胞成熟、肥大并被骨取代。尽管这种发育分叉对骨骼形成和功能的至关重要性已被广泛认识，但其潜在的调控机制仍不清楚，特别是在分子水平上。在上一个资助期，我们专注于转录因子ERG及其变体C-1-1。用鸡和人C-1-1进行的功能获得研究表明：（a）C-1-1能够在整个肢体软骨细胞群上施加稳定的和关节样表型，阻断生长板形成、软骨细胞成熟和骨形成;（B）C-1-1抵消促成熟转录因子Runx 2的作用;和（c）关节主调节因子GDF-5在发育中的滑膜关节中快速诱导ERG/C-1-1表达。这些和其他发现导致我们对这种竞争性延续提议的中心假设：（a）C-1-1作用于GDF-5下游，有助于形成永久性关节软骨细胞;（B）C-1-1反过来抑制Runx 2功能，维持细胞的永久状态，并防止成熟和肥大。我们的目标是：（i）通过细胞和外植体培养物以及转基因方法功能性表征鼠ERG变体;（ii）使用GDF-5-Cre和GDF-5-CreER小鼠确定发育或出生后生命期间条件性ERG基因消融的后果;以及（iii）确定GDF-5通过信号传导途径和启动子作用触发ERG表达的机制，以及ERG/C-1-1如何抑制Runx 2功能。该项目将产生对关节软骨细胞的发生和功能的基本见解。它还应该产生退行性关节疾病的小鼠模型，可用于测试未来骨关节炎患者和老年人常见关节疾病的基因和细胞疗法。

DESCRIPTION (provided by applicant): During limb skeletogenesis chondrocytes follow two developmental paths and produce permanent articular cartilage persisting through life or transient growth plate cartilage in which the cells mature, hypertrophy, and are replaced by bone. Though the critical importance of this developmental bifurcation for skeletal formation and function is widely recognized, the underlying mechanisms of regulation remain unclear, particularly at the molecular level. In the previous funding period, we focused on the transcription factor ERG and its variant C-1-1. Gain-of-function studies with chick and human C-1-1 show that: (a) C-1-1 is able to impose a stable and articular-like phenotype over the entire limb chondrocyte population, blocking growth plate formation, chondrocyte maturation and bone formation; (b) C-1-1 counteracts action of the pro-maturation transcription factor Runx2; and (c) the joint master regulator GDF-5 rapidly induces ERG/C-1-1 expression in developing synovial joints. These and other findings lead to our central hypotheses for this competitive continuation proposal: (a) C-1-1 acting down-stream of GDF-5 contributes to formation of permanent articular chondrocytes; and (b) C-1-1 in turn inhibits Runx2 function, maintains the permanent status of the cells, and prevents maturation and hypertrophy. Our aims are: (i) to functionally characterize murine ERG variants by cell and explant cultures and transgenic approaches; (ii) determine the consequences of conditional ERG gene ablation during development or postnatal life, using GDF-5-Cre and GDF-5-CreER mice; and (iii) determine the mechanisms by which GDF-5 triggers ERG expression by signaling pathways and promoter action, and how ERG/C-1-1 inhibits Runx2 function. The project will produce fundamental insights into genesis and function of articular chondrocytes. It should also generate mouse models of degenerative joint disease that could be used to test future gene- and cell-based therapies for joints conditions common to osteoarthritic patients and aging individuals.