Basic research to clarify the mechanism of delayed tooth eruption in cleidocranial dysplasia

1)锁骨颅骨发育不良（CCD）以锁骨和颅骨发育不全为特征，其病因是RUNX2/CBFA1基因突变。Runx2/ CBFA1是Runx2/ CBFA1的小鼠同源物，该基因杂合的Runx2/ CBFA1基因缺陷小鼠与CCD的骨异常相似。CCD经常伴有多牙、嵌塞和牙齿延迟出牙，然而，这些原因尚不清楚。为了阐明这些观点，我们对杂合小鼠的牙齿和牙周组织进行了检查。杂合小鼠与正常小鼠在牙骨质和牙周韧带的形成及牙骨质数量上均无差异。然而，前者的牙齿出牙时间明显晚于后者。前者位于喷发通路的破骨细胞数量明显减少。以上结果提示，由于RUNX2/CBFA1单倍性不足导致的破骨细胞募集受损是导致ccd乳牙延迟萌牙的原因之一。2)乳牙萌牙过程分为萌牙通路形成和牙齿垂直运动。我们报道了甲状旁腺激素相关蛋白（PTHrP）和RANKL在前一个过程中的作用和功能。我们还开发了一种新的培养系统来检测破骨细胞的形成和激活，利用萌牙和牙周组织。3)由于牙周韧带（PDL）在牙齿萌牙过程中起着重要的作用，我们采用DNA芯片技术比较了萌牙和非萌牙分离的PDL基因表达。有趣的是，CALBINDINi的表达在大鼠实验牙齿运动过程中在PDL受压侧也有高表达，在萌牙的PDL中比在非萌牙的PDL中明显更高。

1) The cause of the Cleidocranial dysplasia (CCD), characterized by hypoplastic clavicle and cranial bones, is known as a gene mutation of RUNX2/CBFA1. Runx2/Cbfal is a mouse homolog of RUNX2/CBFA1 and heterozygous Runx2/Cbfa1 gene-deficient mice of this gene resembles to the bone abnormalities in CCD. CCD frequently accompanies supernumerary teeth and impaction and delayed eruption of teeth, however, these causes are yet not known. To clarify these points, teeth and periodontal tissues were examined in heterozygous mice. The number of teeth or the formation of cementum and periodontal ligament did not show difference between heterozygous and normal mice. However, the timing of tooth eruption into the oral cavity was significantly delayed in the former than in the latter. The osteoclast number located in the eruption pathway was significantly lower in the former., These observations suggest that impaired osteoclast recruitment due to the haploinsufficiency of RUNX2/CBFA1 as one of the cause of the delayed tooth eruption in CCD.2) The process of tooth eruption is divided into the eruption 'pathway formation and vertical tooth movement. We reported the contribution and function of parathyroid hormone-related protein (PTHrP) and RANKL in the former process. We also developed a novel culture system to assay the osteoclast formation and activation using the erupting teeth and periodontal tissues.3) Since the periodontal ligament (PDL) is known to play an important role during the tooth eruption, DNA microarray was carried out to compare the gene expression of PDL isolated from erupting and non-erupting teeth. Interestingly, the expression of CALBINDINi, which is also known to show high expression in the compression side of the PDL during the experimental tooth movement in rats, was dramatically higher in PDLs from erupting teeth than non-erupting teeth.