Cobourne Martyn T, Mitsiadis Thimios
Department of Orthodontics and Craniofacial Development, GKT Dental Institute, King's College London, London SE19RT, UK.
J Exp Zool B Mol Dev Evol. 2006 May 15;306(3):251-60. doi: 10.1002/jez.b.21084.
The mammalian dentition is composed of serial groups of teeth, each with a distinctive crown and root morphology, highly adapted to its particular masticatory function. In the embryo, generation of individual teeth within the jaws relies upon interactions between ectoderm of the first branchial arch and the neural crest-derived ectomesenchymal cells that migrate into this region from their site of origin along the neural axis. Classic tissue recombination experiments have provided evidence of an essential role of the ectoderm in initiating tooth development; however, the underlying ectomesenchyme rapidly acquires dominance in establishing shape. A key question is how these cells acquire this positional information. One theory suggests that ectomesenchymal cells are pre-patterned with respect to shape generation. Alternatively, this cell population acquires positional information within the first branchial arch itself, following migration. Recent molecular evidence suggests a high degree of plasticity within these ectomesenchymal cells. In particular, signalling molecules within the ectoderm exert a time-dependent influence upon the ectomesenchyme by establishing specific domains of homeobox gene expression. Initially, these ectomesenchymal cells are plastic and able to respond to signalling from the ectoderm, however, this plasticity is rapidly lost and pattern information becomes fixed. Therefore, in the first branchial arch, local regulation between the ectoderm and neural crest-derived ectomesenchyme is crucial in establishing the appropriate tooth shape in the correct region of the jaw.
哺乳动物的牙列由一系列牙齿组成，每颗牙齿都有独特的牙冠和牙根形态，高度适应其特定的咀嚼功能。在胚胎中，颌骨内单个牙齿的生成依赖于第一鳃弓的外胚层与神经嵴衍生的外胚间充质细胞之间的相互作用，这些细胞从其起源部位沿神经轴迁移到该区域。经典的组织重组实验已经证明外胚层在启动牙齿发育中起着至关重要的作用；然而，潜在的外胚间充质在确定形状方面迅速占据主导地位。一个关键问题是这些细胞如何获得这种位置信息。一种理论认为，外胚间充质细胞在形状生成方面预先形成了模式。另一种观点认为，这群细胞在迁移后在第一鳃弓自身内部获得位置信息。最近的分子证据表明这些外胚间充质细胞具有高度的可塑性。特别是，外胚层内的信号分子通过建立同源框基因表达的特定区域，对外胚间充质施加时间依赖性影响。最初，这些外胚间充质细胞具有可塑性，能够对外胚层的信号作出反应，然而，这种可塑性很快就会丧失，模式信息变得固定。因此，在第一鳃弓中，外胚层与神经嵴衍生的外胚间充质之间的局部调节对于在颌骨的正确区域建立合适的牙齿形状至关重要。
