Lumsden A G
Division of Anatomy, United Medical and Dental Schools, Guy's Hospital, London.
Development. 1988;103 Suppl:155-69. doi: 10.1242/dev.103.Supplement.155.
Teeth develop from composite organ rudiments that are formed through the interaction of oral epithelium and mesenchyme of the first branchial arch; cells of the former differentiate into enamel-secreting ameloblasts whereas those of the latter differentiate into dentine-secreting odontoblasts. Experimental analysis of odontogenic tissue interactions in mammalian embryos has focused on the late developmental stages of morphogenesis and cytodifferentiation; little is known about initial pattern-forming events, during which presumptive tooth-forming cells are specified and the sites of tooth initiation become established. It requires to be shown, for example, whether the mesenchymal cells of mammalian teeth are derived, like those of amphibians, from the cranial neural crest, and if so, whether these form a specified subpopulation in the neural folds. Alternatively, are they specified after migration into the mandibular arch, possibly by interaction with the oral epithelium? The developmental potentials of mouse embryo premigratory cranial neural crest cells (CNC - explanted from the caudal mesencephalic and rostral metencephalic neural folds) have been studied in intraocular homograft recombinations with various regions of embryonic surface ectoderm. Cartilage, bone and neural tissue developed in all combinations of CNC and epithelium. Teeth formed in combinations of CNC with mandibular arch epithelium but not in combinations of CNC with limb bud epithelium. Teeth also formed in combinations of mandibular arch epithelium with neural crest explanted from the trunk level. These results indicate that mammalian neural crest has an odontogenic potential but that this is not restricted to the crest of presumptive tooth-forming levels. Normal migration appears not to be a prerequisite for expression of odontogenic potential but this does require an interaction with region-specific epithelium. It is reasonable to infer that during normal development the neural crest that enters the mandibular arch is odontogenically unspecified before or during migration and that the oral epithelium is the earliest known site of tooth pattern.
牙齿由复合器官原基发育而来，这些原基通过第一鳃弓的口腔上皮和间充质的相互作用形成；前者的细胞分化为分泌釉质的成釉细胞，而后者的细胞分化为分泌牙本质的成牙本质细胞。对哺乳动物胚胎中牙源性组织相互作用的实验分析主要集中在形态发生和细胞分化的后期发育阶段；对于初始模式形成事件知之甚少，在此期间，假定的成牙细胞被指定，牙齿起始部位得以确立。例如，需要证明哺乳动物牙齿的间充质细胞是否像两栖动物的间充质细胞一样，来源于颅神经嵴，如果是，这些细胞在神经褶中是否形成一个特定的亚群。或者，它们是在迁移到下颌弓后，可能通过与口腔上皮的相互作用而被指定的吗？通过与胚胎表面外胚层的各个区域进行眼内同种异体移植重组，研究了小鼠胚胎迁移前颅神经嵴细胞（CNC——从尾侧中脑和头侧后脑神经褶中分离出来）的发育潜能。在CNC和上皮的所有组合中都发育出了软骨、骨和神经组织。牙齿在CNC与下颌弓上皮的组合中形成，但在CNC与肢芽上皮的组合中未形成。牙齿也在与从躯干水平分离出来的神经嵴的下颌弓上皮组合中形成。这些结果表明，哺乳动物神经嵴具有牙源性潜能，但这并不局限于假定的成牙水平的嵴。正常迁移似乎不是牙源性潜能表达的先决条件，但这确实需要与区域特异性上皮相互作用。有理由推断，在正常发育过程中，进入下颌弓的神经嵴在迁移前或迁移过程中牙源性未被指定，而口腔上皮是最早已知的牙模式部位。
