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的调控蛋白以及一般的调控蛋白。许多这些因子、它们的同源元件和它们的功能辅助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体，以选择性地激活或抑制靶基因以响应生理信号。转录因子Runx2的零突变表明，它在胚胎发育过程中是软骨内成骨、成骨细胞分化和骨形成所必需的。然而，Runx2在早期表达增加，成骨细胞增殖与骨量减少和骨折有关。靶向干扰Runx2基因的小鼠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形成、骨重建、骨折愈合和衰老的影响的特征。我们的假设是Runx2是一个主开关，有助于控制成人骨骼的骨形成和重塑，这一假说将通过出生后调节的Runx2蛋白的消融来解决。这项提议的目标是建立一种有条件的小鼠模型，在该模型中，Runx2在选定的胚胎和产后阶段以细胞类型和组织特异性的方式失活。在目标1中，在调控启动子的控制下，将产生一个携带外显子8两侧loxP位点的转基因小鼠，用于Cre重组酶在体内和体外的功能失活。目的建立并鉴定可诱导的、骨骼组织特异的Cre转基因小鼠。目的3通过对不同年龄成人骨骼的表型分析，确定Runx2在成人骨骼骨形成和改建中的作用。我们的长期目标是使用这种有条件的小鼠模型来确定Runx2在增加骨转换和骨折愈合过程中的功能。这些研究将提供对成骨细胞分化过程中Runx2调控的分子机制的见解，这些机制可能被转化为治疗先天性和退行性骨骼疾病、代谢性骨骼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.