Genetic Control of Osteoblast Differentiation

描述(申请人提供)：类似于其他器官的形成，骨骼形成涉及两大类调节因素。图案化因素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初始决定，而分化因素控制骨骼组成细胞的命运。以往的细胞生物学实验表明，成骨细胞的分化是一个多步骤的过程。最近，转录因子Cbfa1/Runx2被证明是成骨细胞分化所必需的。最近，我们发现Kruppel转录因子家族中的一个新成员，称为Osterix(OSX)，是骨形成和成骨细胞分化所必需的。OSX基因缺失的小鼠虽然软骨细胞分化和软骨形成正常，但没有膜，也没有软骨内骨。此外，我们的实验表明，OSX在Cbfa1/Runx2下游起作用。这项应用旨在描述OSX控制成骨细胞分化的机制。我们计划检测由OSX控制的成骨细胞遗传程序的程度，并在体内鉴定直接介导OSX在成骨细胞中转录激活的靶基因序列。我们的研究还将确定与OSX物理或功能相互作用的蛋白质，或控制其活性的蛋白质。最后，我们将确定OSX是否是Sox9表达和软骨细胞分化计划的负调控因子。总体而言，这些实验将极大地提高我们对成骨细胞分化的分子机制的理解。

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.