Morriss-Kay G, Tucket F
Department of Human Anatomy, University of Oxford, England.
J Craniofac Genet Dev Biol. 1991 Oct-Dec;11(4):181-91.
Head-trunk differences are well established in the most primitive vertebrates, and are clear from early developmental stages of all modern forms. The boundary between the two regions is not constant in all vertebrate classes in terms of the number of occipital somites. The occipital region is in some respects a transitional zone, giving rise to trunk-like somitic derivatives in the head. It is also highly specialised, providing a unique population of neural crest cells that are essential for formation of the aorticopulmonary septum (which divides the outflow tract of the heart) in mammals and birds. In the preoccipital hindbrain, rhombomeres represent a segmental structural pattern that is quite distinct from that of the somites, with a segment-specific pattern of gene expression. Expression of some of these genes in mesenchyme close to the primitive streak at earlier stages suggests that this pattern may be established at the time of neural induction. Mammalian embryos have taken cranial specialization further than other classes of vertebrate, particularly in relation to the pattern of development and eventual structural complexity of the forebrain. Mammalian specialisations of craniofacial development are described through references to studies on cranial neurulation, on cranial neural crest cell migration, and on the possible morphogenetic roles of extracellular matrix components.
头与躯干的差异在最原始的脊椎动物中已得到充分证实，并且在所有现代形式的早期发育阶段就很明显。就枕部体节的数量而言，这两个区域之间的边界在所有脊椎动物类别中并非恒定不变。枕部区域在某些方面是一个过渡区，在头部产生类似躯干的体节衍生物。它也高度特化，提供了一群独特的神经嵴细胞，这些细胞对于哺乳动物和鸟类主动脉肺动脉隔（分隔心脏流出道）的形成至关重要。在枕前后脑，菱脑节代表一种与体节截然不同的节段性结构模式，具有特定节段的基因表达模式。其中一些基因在早期靠近原条的间充质中的表达表明，这种模式可能在神经诱导时就已建立。哺乳动物胚胎的颅骨特化比其他脊椎动物类别更进一步，特别是在前脑的发育模式和最终的结构复杂性方面。通过参考关于颅骨神经胚形成、颅骨神经嵴细胞迁移以及细胞外基质成分可能的形态发生作用的研究，描述了颅面发育的哺乳动物特化。
