Hunt P, Whiting J, Nonchev S, Sham M H, Marshall H, Graham A, Cook M, Allemann R, Rigby P W, Gulisano M
Lab of Eukaryotic Molecular Genetics, MRC-National Institute for Medical Research, Mill Hill, London, UK.
Dev Suppl. 1991;Suppl 2:63-77.
In this study we have examined the expression of murine Hox homeobox containing genes by in situ hybridisation in the branchial region of the head. Genes from the Hox complexes display segmentally restricted domains of expression in the developing hindbrain, which are correlated with similar restricted domains in the neural crest and surface ectoderm of the branchial arches. Comparison of related genes from the different clusters shows that subfamily members are expressed in identical rhombomeres and branchial arches. These patterns suggest a combinatorial system for specifying regional variation in the head, which we refer to as a Hox code. The Hox genes also display dynamic dorso-ventral (D-V) restrictions in the developing neural tube which mirror the timing and spatial distributions of the birth of major classes of neurons in the CNS. Genes in the Hox-2 cluster all have a similar D-V distribution that differs from that of genes from the other Hox clusters, and suggests that members of a subfamily may be used to specify positional values to different subsets of cells at the same axial level. These results are discussed in terms of a system for patterning the branchial regions of the vertebrate head, and evolution of head structures. We have also examined aspects of the transcriptional regulation of Hox-2 genes in transgenic mice using a lacZ reporter gene. We have been able to reconstruct the major pattern of the Hox-2.6 gene on the basis of identical expression of the transgene and the endogenous gene with respect to timing, spatial restrictions and tissue-specific distributions. Deletion analysis has enabled us to identify three regions involved in generating this pattern. Two of these regions have the properties of enhancers which are capable of imposing spatially-restricted domains of expression on heterologous promoters. We have generated similar Hox-lacZ fusions that reconstruct the highly restricted patterns of the Hox-2.1 and Hox-2.8 genes in the developing nervous system, supporting our in situ analysis and the idea of a Hox code. These transgenic experiments are a useful step in examining regulation in the Hox cascade.
在本研究中，我们通过原位杂交技术检测了含小鼠Hox同源框基因在头部鳃区的表达情况。来自Hox复合体的基因在发育中的后脑呈现出节段性受限的表达域，这与鳃弓神经嵴和表面外胚层中类似的受限域相关。对不同基因簇中相关基因的比较表明，亚家族成员在相同的菱脑节和鳃弓中表达。这些模式提示了一种用于确定头部区域差异的组合系统，我们称之为Hox编码。Hox基因在发育中的神经管中也表现出动态的背腹（D-V）限制，这反映了中枢神经系统中主要神经元类群诞生的时间和空间分布。Hox-2基因簇中的基因都具有相似的D-V分布，这与其他Hox基因簇中的基因不同，表明一个亚家族的成员可能用于为同一轴水平上不同细胞亚群指定位置值。我们从脊椎动物头部鳃区的模式形成系统以及头部结构的进化方面对这些结果进行了讨论。我们还利用lacZ报告基因研究了转基因小鼠中Hox-2基因的转录调控方面。基于转基因和内源基因在时间、空间限制和组织特异性分布方面的相同表达，我们已经能够重建Hox-2.6基因的主要模式。缺失分析使我们能够确定参与产生这种模式的三个区域。其中两个区域具有增强子的特性，能够在异源启动子上施加空间受限的表达域。我们构建了类似的Hox-lacZ融合体，它们在发育中的神经系统中重建了Hox-2.1和Hox-2.8基因的高度受限模式，支持了我们的原位分析以及Hox编码的观点。这些转基因实验是研究Hox级联调控的有益步骤。
