Role of Transcription Factor ERG in Skeletogenesis

描述（由申请人提供）：在肢体骨骼形成过程中，软骨细胞遵循两种发育途径，产生终身存在的永久性关节软骨或短暂生长的板软骨，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关键重要性已被广泛认识，但其潜在的调节机制仍不清楚，特别是在分子水平上。在之前的融资期内，我们专注于转录因子ERG及其变体C-1-1。对鸡和人C-1-1的功能获得性研究表明：(a) C-1-1能够在整个肢体软骨细胞群中施加稳定的关节样表型，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Runx2的作用；(c)关节主调控因子GDF-5在发育中的滑膜关节中快速诱导ERG/ c -1-1表达。这些和其他的发现导致了我们对这个竞争性延续提议的中心假设：(a) C-1-1作用于GDF-5的下游有助于永久性关节软骨细胞的形成；(b) C-1-1反过来抑制Runx2功能，维持细胞的永久状态，防止成熟和肥大。我们的目标是：(i)通过细胞和外植体培养以及转基因方法对小鼠ERG变体进行功能表征；（ii）使用GDF-5-Cre和GDF-5-CreER小鼠，确定在发育或出生后条件ERG基因消融的后果；（iii）确定GDF-5通过信号通路和启动子作用触发ERG表达的机制，以及ERG/C-1-1如何抑制Runx2功能。该项目将对关节软骨细胞的发生和功能产生根本性的见解。它还应该产生退行性关节疾病的小鼠模型，可用于测试未来基于基因和细胞的治疗方法，以治疗骨关节炎患者和老年人常见的关节疾病。

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.