Runx in Embryonic and Postnatal Skeletogenesis

描述（由申请人提供）： 体内成骨的转录调控是一个复杂的过程，涉及大量的基因和表型特异性以及一般的调节蛋白。这些因子中的许多因子、它们的同源元件和它们的功能辅因子都以限速浓度存在，并且必须组装成不同的多组分调节复合物，以响应生理线索选择性地激活或抑制靶基因。Runx2转录因子的突变，已经表明它在胚胎发育期间对于软骨内骨化、成骨细胞分化和骨形成是必需的。然而，Runx 2在早期阶段的表达增加，增殖的成骨细胞与骨量减少和骨折有关。Runx2基因靶向破坏小鼠的胚胎和新生儿致死率排除了编码的调节因子对出生后骨骼发生、骨重塑、骨折愈合和衰老的影响。我们的假设，Runx2是一个主开关，有助于控制骨形成和重塑的成人骨骼将实验解决的Runx2蛋白的调节出生后消融。该提案的目标是产生条件小鼠模型，其中Runx2在选定的胚胎和出生后阶段以细胞类型和组织特异性方式失活。在目的1中，将产生携带外显子8侧翼的LoxP位点的转基因小鼠，用于在受调控的启动子的控制下通过Cre重组酶进行体内和离体功能失活。目的2建立可诱导的、骨骼组织特异性的Cre转基因小鼠并对其进行鉴定。目的3将通过不同年龄的表型分析来确定Runx 2在成人骨骼骨形成和重塑中的作用。我们的长期目标是使用这种条件性小鼠模型来定义Runx2在骨转换增加和骨折愈合过程中的功能。这些研究将为Runx2在成骨细胞分化过程中的分子机制提供见解，这些机制可能会转化为先天性和退行性骨骼疾病，代谢性骨疾病或骨肿瘤的新疗法。

DESCRIPTION (provided by applicant): Transcriptional control of osteogenesis in vivo is a complex process involving a large number of genes and phenotype specific as well as general regulatory proteins. Many of these factors, their cognate elements and their functional co-factors are all present in a rate limiting concentration, and must assemble into distinct multi-component regulatory complexes to selectively activate or suppress target genes in response to physiological cues. Null mutation of the Runx2 transcription factor, has shown that it is obligatory for endochondral ossification, osteoblast differentiation and bone formation during embryonic development. However, increased expression of Runx2 in early stage, proliferating osteoblasts is linked with osteopenia land bone fractures. Embryonic and neonatal lethality of mice with targeted disruption of the Runx2 gene precludes characterizing the impact of the encoded regulatory factor on postnatal skeletogenesis, bone remodeling, fracture healing and aging. Our hypothesis that Runx2 is a master switch which contributes to control of bone formation and remodeling of the adult skeleton will be experimentally addressed by regulated postnatal ablation of the Runx2 protein. The goal of this proposal is to generate a conditional mouse model where Runx2 is inactivated in a cell type and tissue-specific manner, at selected embryonic and postnatall stages. In Aim 1, a transgenic mouse carrying LoxP sites flanking exon 8 will be generated for in vivo and ex vivo functional inactivation by Cre recombinase under the control of a regulated promoter. Aim 2 will generate and characterize the inducible and skeletal tissue specific Cre transgenic mouse. Aim 3 will identify the role of Runx2 in bone formation and remodeling of the adult skeleton through phenotype analysis at different ages. Our long-term objective is to use this conditional mouse model to define the Runx2 function during increased bone turnover and fracture healing. These studies will provide insights into the molecular mechanisms governed by Runx2 during osteoblast differentiation that may be translated to novel therapies for congenital and degenerative skeletal diseases, metabolic bone disorders or bone tumors.