Role of novel transcription factor on bone formation

我们报道Osr2是成骨细胞功能的调节因子之一，因为显性阴性的Osr2转基因小鼠表现出成骨细胞活性降低，以及颅骨和胫骨骨组织矿化延迟。我们的研究结果表明Osr2在成骨细胞增殖调控中起作用。控制骨形成的分子机制已受到越来越多的关注，相关知识的遗传控制成骨细胞分化。奇跳相关基因（Osr）是一种锌指转录因子，最近被认为与骨形成有关，尽管对其作用知之甚少。为了阐明Osr2在体内的功能，我们构建了过表达显性负Osr2的转基因小鼠。在本研究中，n端缺失的Osr2被发现是Osr1和Osr2的显性负突变体。显性阴性Osr2 （Osr2ΔN）转基因小鼠在颅骨和皮质骨组织中表现出延迟矿化。此外，转基因小鼠骨骼的软x射线分析显示明显增加的透光率。用阿利新蓝和茜素红染色的新生Osr2ΔN转基因小鼠骨骼检查显示颅骨和骨骼元素的强度降低。在形态学上，Osr2ΔN转基因小鼠的颅骨和胫骨由明显变薄的顶骨和皮质骨组成，骨表面成骨细胞数量减少，表明成骨细胞增殖减少。此外，从Osr2ΔN转基因小鼠获得的颅骨成骨细胞显示出高度减弱的成骨细胞分化和增殖，证实Osr2是成骨所必需的。最后，runx2缺陷细胞实验结果表明，Osr2诱导ALP表达，但程度低于runx2表达细胞。我们的遗传观察表明，Osr2基因在成骨细胞增殖中起关键作用。

We report that Osr2 is one of the regulators of osteoblast function, since dominant-negative Osr2 transgenic mice exhibited decreased osteoblast activity, as well as delayed mineralization in calvarial and tibial bone tissues. Our results indicate that Osr2 functions in regulation of osteoblast proliferation. Molecular mechanisms that control bone formation have received attention with increasing knowledge related to genetic control of osteoblast differentiation. The odd-skipped related (Osr) gene is a zinc-finger transcription factor recently suggested to be involved in bone formation, though little is known about its role. To elucidate the in vivo function of Osr2, we generated transgenic mice overexpressing dominant-negative Osr2. In the present study, N-terminal deleted Osr2 was found to act as a dominant-negative mutant toward both Osr1 and Osr2. Dominant-negative Osr2 (Osr2ΔN) transgenic mice demonstrated delayed mineralization in calvarial and cortical bone tissues. Further, soft X-ray analysis of transgenic mice bones revealed distinctly increased radiolucency. Examinations of newborn Osr2ΔN transgenic mice skeletons stained with alcian blue and alizarin red showed reduced intensities in the skull and skeletal elements. Morphologically, calvaria and tibia of Osr2ΔN transgenic mice were composed of markedly thinner parietal and cortical bones, and lower numbers of osteoblastic cells on bone surfaces, indicating a reduced proliferation of osteoblasts. Further, calvarial osteoblasts obtained from Osr2ΔN transgenic mice showed highly attenuated osteoblast differentiation and proliferation, confirming that Osr2 is required for osteogenesis. Finally, results of Runx2-deficient cell assays suggested that Osr2 induces ALP expression, but to a lesser degree than Runx2-expressing cells. Our genetic observations showed that the Osr2 gene plays a key role in osteoblastic cell proliferation.