Molecular Genetics Of Tooth Development

牙齿发育的分子遗传学

• 批准号: 6814544
• 负责人: Ashok B. KULKARNI
• 金额: --
• 依托单位: NATIONAL INSTITUTE OF DENTAL & CRANIOFACIAL RESEARCH
• 依托单位国家: 美国
• 资助国家: 美国
• 起止时间: 至
• 项目状态: 未结题
• 来源: https://reporter.nih.gov/project-details/6814544
• 关键词: congenital dentition disorder; dental development; dental disorder; dentin; dentinogenesis; developmental genetics; disease /disorder model; extracellular matrix; gene expression; gene targeting; genetically modified animals; growth factor; laboratory mouse; molecular cloning; molecular genetics; normal ossification; osteogenesis imperfecta; transcription factor

Tooth development depends on reciprocal interactions between oral epithelium and mesenchyme. The mesenchymal-derived odontoblasts secrete several collagenous and non-collagenous proteins to form a unique extracellular matrix . Among the non-collagenous proteins, dentin sialoprotein (Dsp) and dentin phosphoproteins (Dpp) are highly tooth-specific and are believed to play a crucial role in converting predentin to form mineralized dentin. These two proteins are derived from the cleavage of a 940 amino acid polypeptide, dentin sialophosphoprotein (Dspp). The Dspp gene consists of 5 exons spanning 16 kb and is transcribed as 4.4 kb mRNA . Messenger RNA for Dspp is expressed predominantly by odontoblasts and transiently by pre-ameloblasts. However, recently low levels of Dspp were observed in the ear and in bone. The Dsp, the amino terminal part of Dspp, is sialic acid rich and glycosylated protein that shares similarities with the other sialoproteins including bone sialoprotein, dentin matrix protein-1, and osteopontin. The Dpp, a highly phosphorylated protein with repeats of aspartic acid and phosphoserine, is thought to play a key role in the nucleation of hydroxyapatite formation during dentin calcification. Due to its restricted expression, and its physical localization on the human chromosome 4q within the dentinogenesis imperfecta-II (DGI-II) locus, Dspp was implicated as a potential candidate gene for this disorder. The other important genes involved in biomineralization mapped to this region of chromosome 4q include dentin matrix protein-1, bone sialoprotein, DSPP and osteopontin. Dentinogenesis imperfecta (DGI), an autosomal dominant disorder of the tooth that primarily affects dentin biomineralization, is classified into three subtypes based on the clinical features in an order of degree severity with type-I being the least severe and type-III the most severe . DGI-I is associated with osteogenesis imperfecta while the more severe forms (DGI-II and DGI-III) are restricted to the dentin. Opalescent dentin with an obliterated pulp chambers are the characteristic features in DGI-II. The teeth of patients with DGI-III are referred to as shell teeth in which the dentin mineralization does not occur after mantle dentin is formed. Radiographically, the pulp cavities in these teeth appear as enlarged pulp chambers along with high incidence of pulp exposures .Recently, several mutations in the Dspp gene have been identified in families with DGI-II disorder. These mutations include a C-T transition at the end of 3rd exon (Gln45stop) resulting in a premature termination of Dspp protein, G-A transition mutation in intron 3 (splice donor site) causing exon skipping, and Pro17Thr and Val18Phe transitions. Dentin dysplasia-II (DD-II), another human disorder of dentin mineralization, that shares similarities with DGI-II, and is attributed to a Tyr6Asp protein transition mutation in the hydrophobic core sequence of dspp gene. This mutation disabled the entry of Dspp into the endoplasmic reticulum . All these mutations indicate a potential function for Dspp in tooth mineralization. In order to characterize the molecular events that control dentin mineralization during normal tooth development and disease, we have deleted the entire Dspp coding region in embryonic stem (ES) cells and generated Dspp -/- mice. These null mice displayed an enlarged pulp cavity, widened predentin zone, decreased dentin width and high incidence of pulp exposures similar to DGI-III. Additionally, these mice showed an increased accumulation of biglycan and decorin within the widened predentin and scalloped (void spaces) regions in the dentin correlating well with defective mineralization. Amelogenins form a major protein component of developing enamel and are predominantly involved in the formation of enamel. Additionally, amelogenins have been implicated in the formation and maintenance of cementum. However, their precise expression profile and molecular role in the cementogenesis are not well understood. We have identified for the first time expression of the splice variants of amelogenin mRNA in the periodental region of tooth roots of the wild-type mice but not in the amelogenin-null mice. Progressive cementum defects in the amelogenin-null mice are associated with the increased expression of RANKL, an essential molecule for osteoclastogenesis, in cementoblast/periodontal ligament cells. These findings indicate a novel role for the amelogenin proteins, derived from the splice variants, in regulating RANKL pathway affecting the maintenance of cementum through osteoclastogenisis.

牙齿发育取决于口腔上皮和间质之间的相互相互作用。间充质衍生的牙本质细胞分泌几种胶原蛋白和非胶原蛋白形成独特的细胞外基质。在非胶原蛋白中，牙本质唾液蛋白（DSP）和牙本质磷蛋白（DPP）高度牙齿特异性，被认为在转化preadentin以形成矿物化牙本质方面起着至关重要的作用。这两种蛋白质源自940个氨基酸多肽乙蛋白唾液磷蛋白（DSPP）的裂解。 DSPP基因由5个跨越16 kb的外显子组成，被转录为4.4 kb mRNA。用于DSPP的Messenger RNA主要由Odontoblasts表示，并通过预成木细胞暂时表达。但是，最近在耳朵和骨头中观察到了低水平的DSPP。 DSP是DSPP的氨基末端部分，是富含唾液酸和糖基化的蛋白，与其他唾液蛋白具有相似性，包括唾液蛋白，唾液蛋白，牙本质基质蛋白-1和骨teopontin。 DPP是一种高度磷酸化的蛋白质，具有天冬氨酸和磷酸碱的重复序列，被认为在牙本质钙化期间在羟基磷灰石形成的成核中起关键作用。由于其表达受限及其在牙本质发生不完美的II（DGI-II）基因座中的人体染色体4Q上的物理定位，DSPP被认为是该疾病的潜在候选基因。映射到该染色体4Q区域的生物矿化涉及的其他重要基因包括牙本质基质蛋白-1，骨唾液蛋白，DSPP和骨桥蛋白。牙齿生成Imperfecta（DGI）是一种主要影响牙本质生物矿化的牙齿的常染色体显性疾病，根据临床特征的严重程度顺序将三个亚型分类为三个亚型，I型是最严重和最严重的III 。 DGI-I与成骨的Imperfecta有关，而更严重的形式（DGI-II和DGI-III）仅限于牙本质。牙本质带有牙本质腔室是DGI-II的特征。 DGI-III患者的牙齿被称为壳牙齿，在形成地幔牙本质后不会发生牙本质矿化。从射线照相上，这些牙齿中的纸浆腔似乎是果室的扩大，以及果肉暴露的高发生率。这些突变包括在第三外显子（GLN45STP）结束时进行的C-T转变，导致DSPP蛋白的过早终止，内含子3（剪接供体位点）的G-A转变突变导致外显子跳过，Pro17ThR和Val18phe Transitions。牙本质发育不良II（DD-II）是另一种人类矿物质矿化疾病，与DGI-II共享相似之处，并归因于DSPP基因的疏水性核心序列中的Tyr6asp蛋白过渡突变。该突变使DSPP进入内质网。所有这些突变表明DSPP在牙齿矿化中的潜在功能。为了表征在正常牙齿发育和疾病期间控制牙本质矿化的分子事件，我们删除了胚胎干细胞（ES）细胞中的整个DSPP编码区，并产生的DSPP - / - 小鼠。这些无效的小鼠显示出扩大的果肉腔，延伸的前蛋白区，降低了类似于DGI-III的牙髓暴露的牙本质宽度和高发病率。此外，这些小鼠在牙本质中宽扩大的预素蛋白和扇贝（空间空间）区域内的大型群和装饰的积累增加，与有缺陷的矿化良好相关。氨基蛋白蛋白是发育搪瓷的主要蛋白质成分，主要参与牙釉质的形成。另外，氨基蛋白蛋白还与牙骨质的形成和维持有关。但是，它们在胶结发生中的精确表达谱和分子作用尚不清楚。我们已经在野生型小鼠的牙根牙根上，但在amelegenin-null小鼠中首次鉴定了氨基蛋白蛋白mRNA的剪接变体的首次表达。在蛋白质细胞/牙周韧带细胞中，阿米他素蛋白无小鼠中的进行性骨质缺陷与RANKL的表达增加有关，RANKL的表达增加，RANKL的表达是破骨细胞生成的基本分子。这些发现表明，蛋白质蛋白的新作用是源自剪接变体的，在调节RANKL途径中影响骨骼通过骨细胞基因的维持。