The role of IFT80 in bone formation

描述（由申请人提供）：鞭毛内转运（IFT）蛋白是基于微管的转运机制，对于所有纤毛和鞭毛的组装和维持至关重要。最近的研究结果不仅揭示了纤毛和鞭毛在运动、感觉接收和信号传导中的各种作用，而且还证明了IFT在基因调控和表达、细胞增殖和分化以及动物发育和行为中的功能。IFT蛋白的突变导致各种生物体中纤毛和鞭毛的丧失或严重减少，这可导致许多以肾脏、视网膜和骨骼的病理变化的各种组合为特征的人类疾病。有条件地消融IFT 88会破坏hedgehog信号传导，导致多指畸形和软骨内骨形成缺陷。中断Kif 3a，驱动蛋白II的亚基，显示肢体和颅骨骨骼异常。最近，在软骨外胚层发育不良Ellis-van Creveld综合征（EVC）中发现了一种新的蛋白质突变，该蛋白质定位于纤毛基部，并且在小鼠中破坏该基因会导致各种骨骼和颅面异常 以及牙齿和指甲的变化。靶向缺失IFT/纤毛的小鼠具有广泛的 各种骨表型，提供了有趣的见解，个别IFT蛋白在骨形成中的功能。最近，Beales等人的研究小组发现，IFT复合物B的一种新组分--IFT 80在人类中的部分缺失导致人类疾病，如青少年窒息性胸营养不良（JATD）和短肋多指（SRP）III型。这两种疾病都有严重的骨骼异常，包括长骨缩短和胸廓狭窄。然而，目前尚不清楚IFFT 80突变如何导致骨骼异常。我们最近的研究表明，在成骨细胞分化过程中，IFFT 80高度表达。沉默IFFT 80不仅损害纤毛形成，而且通过下调成骨细胞标记基因Runx 2和骨钙素以及刺猬信号（Hh）相关基因shh、Ihh和Gli 2的表达来显著抑制成骨细胞分化。这些都是重要的成果;尽管如此，仍然没有在成骨细胞分化和骨形成中对IFFT 80信号传导的一般需要的体内证据。最近，我们在成骨细胞特异性谱系中建立了IFT 80条件性敲除模型，发现IFT 80突变小鼠表现出明显的生长迟缓和严重的骨异常。基于这些结果，我们推测，IFFT 80通过调节成骨细胞基因表达、分化和Hh/Gli通路在脊椎动物骨形成和正常骨功能中起重要作用。在这个提议中，我们将通过产生一个条件性敲除等位基因来研究IFFT 80在骨形成中的作用，并研究该基因缺失对成骨细胞基因表达、分化和增殖的影响来验证这一假设。本工作的长期目标是了解IFT/纤毛蛋白在骨发育和骨疾病中的作用机制和相互作用。

DESCRIPTION (provided by applicant): Intraflagellar transport (IFT) proteins are microtubule based transport machinery, which are essential for the assembly and maintenance of all cilia and flagella. Recent findings have not only revealed the various roles of cilia and flagella in motility, sensory reception, and signaling, but also demonstrated the function of IFT in the control of gene regulation and expression, cell proliferation and differentiation, and animal development and behavior. The mutation of IFT proteins causes the loss or severe reduction of cilia and flagella in various organisms, which can lead to numerous human diseases characterized by various combinations of pathological changes of kidney, retina, and skeleton. Conditional ablation of IFT88 disrupts hedgehog signaling, with polydactyly and defects of endochondral bone formation. Disruption of Kif3a, a subunit of kinesin II, showed limb and cranial skeletal abnormalities. Recently, a novel protein mutated in chondroectodermal dysplasia Ellis-van Creveld syndrome (EVC) was found to be localized to the base of the cilia, and disruption of this gene in mice results in a variety of skeletal and craniofacial abnormalities as well as alterations in the teeth and nails. Mice with targeted deletion of IFT/cilia have a wide variety of bone phenotypes that provide interesting insights into the function of individual IFT protein in bone formation. Most recently, Beales et al group found that the partial loss of IFT80 in human, a novel component of the IFT complex B, causes human diseases such as Jeune asphyxiating thoracic dystrophy (JATD) and short rib polydactyly (SRP) type III. Both diseases have severe bone abnormalities including shortening of the long bones and constriction of the thoracic cage. However, it is unclear how IFT80 mutation leads to skeletal abnormalities. Our recent studies have shown that IFT80 is highly expressed during osteoblast differentiation. Silencing IFT80 not only impairs cilia formation, but also significantly inhibits osteoblast differentiation through down-regulating the expression of osteoblast marker genes- Runx2 and osteocalcin, and hedgehog signaling (Hh) related genes -shh, Ihh and Gli2. These are important results; nonetheless, there is still no in vivo evidence for a general requirement for IFT80 signaling in osteoblast differentiation and bone formation. Most recently, we have generated IFT80 conditional knockout model in osteoblast specific lineage and found that IFT80 mutant mice showed apparent growth retardation with severe bone abnormalities. Based on these results, we hypothesize that IFT80 plays an essential role in vertebrate bone formation and normal bone function through regulating osteoblast gene expression, differentiation and Hh/Gli pathway. In this proposal, we will test the hypothesis by generating an IFT80 conditional knockout allele to study the role of IFT80 in bone formation and investigating the effect of deletion of this gene on osteoblast gene expression, differentiation and proliferation. The long term objective of this work is to understand the functionmechanism and interactions of IFT/cilia proteins in bone development and bone diseases.