Hunt P, Wilkinson D, Krumlauf R
Laboratory of Eukaryotic Molecular Genetics, National Institute for Medical Research, Mill Hill, London, UK.
Development. 1991 May;112(1):43-50. doi: 10.1242/dev.112.1.43.
The structures of the face in vertebrates are largely derived from neural crest. There is some evidence to suggest that the form of the facial pattern is determined by the crest, and that it is specified before migration as to the structures that is is able to form. The neural crest is able to control the form of surrounding, non-neural crest tissues by an instructive interaction. Some of this cranial crest is derived from a region of the hindbrain that expresses Hox 2 homeobox genes in an overlapping and segment-restricted pattern. We have found that neurogenic and mesenchymal neural crest expresses Hox 2 genes from its point of origin beside the neural plate, during migration and after migration has ceased and that rhombomeres 3 and 5 do not have any expressing neural crest beside them. Each branchial arch expresses a different combination or code of Hox genes in a segment-restricted way. The surface ectoderm over the arches initially does not express Hox genes, and later adopts an expression pattern that reflects that of neural crest that has come to underlie it. We suggest that initially the neural plate and neural crest are spatially specified, while the surface ectoderm is unpatterned. Subsequently some positional information could be transferred to the surface ectoderm as a result of an interaction with the neural crest. Given that the role of the homologous genes in insects is position specification, and that neural crest is imprinted before migration, we suggest that Hox 2 genes are providing part of this positional information to the neural crest and hence are involved in patterning the structures of the branchial arches.
脊椎动物面部的结构很大程度上源自神经嵴。有证据表明，面部模式的形成由神经嵴决定，并且在迁移之前就已确定其能够形成的结构。神经嵴能够通过一种指导性相互作用来控制周围非神经嵴组织的形态。部分颅神经嵴源自后脑的一个区域，该区域以重叠且受节段限制的模式表达Hox 2同源框基因。我们发现，神经源性和间充质神经嵴在其起源于神经板旁的位置、迁移过程中以及迁移停止后都表达Hox 2基因，并且菱脑节3和5旁边没有任何表达神经嵴。每个鳃弓以节段限制的方式表达不同的Hox基因组合或编码。鳃弓上方的表面外胚层最初不表达Hox基因，后来采用一种反映其下方神经嵴表达模式的表达模式。我们认为，最初神经板和神经嵴在空间上是特定的，而表面外胚层没有模式。随后，由于与神经嵴的相互作用，一些位置信息可能会传递给表面外胚层。鉴于同源基因在昆虫中的作用是位置指定，并且神经嵴在迁移前就已被印记，我们认为Hox 2基因正在为神经嵴提供部分这种位置信息，因此参与了鳃弓结构的模式形成。
