Genetic Control of Osteoblast Differentiation

描述（由申请人提供）：与其他器官的形成类似，骨骼发生涉及两大类调节因子。图案化因子控制骨骼元素的形状，大小和数量，以及关于胚胎身体计划的最初决定，而分化因子控制骨骼组成细胞的命运。先前的细胞生物学实验表明成骨细胞的分化是沿着一个多步骤的途径进行的。最近，转录因子Cbfa 1/Runx 2被证明是成骨细胞分化所必需的。最近，我们发现了一个新的成员Kruppel家族的转录因子，称为Osterix（Osx），是骨形成和成骨细胞分化所必需的。Osx基因敲除小鼠没有膜状骨和软骨内骨，尽管软骨细胞分化和软骨形成正常发生。此外，我们的实验表明Osx作用于Cbfa 1/Runx 2的下游。本申请提出了表征Osx控制成骨细胞分化的机制。我们计划研究成骨细胞的遗传程序，是由Osx控制的程度，并确定靶基因中的序列，这些序列直接介导的Osx的这些基因在体内成骨细胞的转录激活。我们的研究还将确定与Osx物理或功能相互作用或控制其活性的蛋白质。最后，我们将确定Osx是否是Sox 9表达和软骨细胞分化程序的负调节因子。总之，这些实验应该大大提高我们的理解成骨细胞分化的分子机制。

DESCRIPTION (provided by applicant): Similarly to the formation of other organs, skeletogenesis involves two broad classes of regulatory factors. Patterning factors control the shape, size and number of skeletal element, as well as initial decisions regarding the body plan of the embryo, whereas differentiation factors control the fate of the constituent cells of the skeleton. Previous cell biological experiments suggested that osteoblast differentiation occurs along a multistep pathway. More recently, the transcription factor Cbfa1/Runx2 was shown to be needed for osteoblast differentiation. Very recently, we have discovered that a novel member of the Kruppel family of transcription factors, called Osterix (Osx), is required for bone formation and osteoblast differentiation. Osx null mice have no membranous, and no endochondral bones, although chondrocyte differentiation and cartilage formation occur normally. Furthermore, our experiments indicate that Osx acts downstream of Cbfa1/Runx2. This application proposes to characterize the mechanisms by which Osx controls osteoblast differentiation. We plan to examine the extent of the osteoblast-genetic program that is controlled by Osx and identify sequences in target genes that directly mediate the transcriptional activation by Osx of these genes in osteoblasts in vivo. Our studies will also identify the proteins that either physically or functionally interact with Osx, or control its activity. Finally, we will determine whether Osx is a negative regulator of Sox9 expression and of the chondrocyte differentiation program. Overall, these experiments should greatly improve our understanding of the molecular mechanisms of osteoblast differentiation.