Vogels R, Charité J, de Graaff W, Deschamps J
Hubrecht Laboratory, The Netherlands Institute for Developmental Biology, Utrecht.
Development. 1993 May;118(1):71-82. doi: 10.1242/dev.118.1.71.
The Hox genes have been proved to be instrumental in establishing the positional identity of cells along the embryonic anteroposterior (A-P) axis. Studying the regulation of these genes is a first step toward elucidating the molecular basis of regionalization during embryogenesis. We report here on the identification of cis-acting elements controlling the expression of Hoxb-7 (Hox-2.3). We show that elements driving A-P restricted gene expression are located within the 3.5 kb proximal upstream sequences of the Hoxb-7 gene. A deletion analysis provides evidence for at least three cis-acting control elements upstream from Hoxb-7, and for cooperative interactions between some of these elements in generating the A-P restricted transgenic pattern. One element, conferring by itself Hox-like expression boundaries to the transgene, has been studied in more detail and found to act in an orientation-and promoter-dependent manner. Together the 3.5 kb sequences proximal to Hoxb-7 mediate A-P restricted Hoxb-7/lacZ gene expression in a domain showing rostral boundaries more posterior than those of Hoxb-7. The evolution throughout embryogenesis of the expression pattern of a transgene carrying these sequences has been analysed and shown to mimick that of the endogenous gene, except for a slight delay in the initial expression. We conclude that the transgenes that we tested, spanning a total of 27 kb genomic sequences, do not reproduce all the features of the Hoxb-7 expression pattern. The differences in expression between Hoxb-7 and the transgenes may reveal an aspect of the Hox regulation for which either remote cis-acting control elements and/or gene clustering is required. Additional features that may have favoured maintenance of clustered organisation during evolution are partial overlap of transcription units with the regulatory regions of the neighbouring genes, and cis-regulatory interactions between multiple Hox genes: not only do cis-acting control elements of the Hoxb-7 gene map in the 3' untranslated sequences of the Hoxb-8 (Hox-2.4) gene, but our experiments suggest that Hoxb-7 control sequences modulate expression of the Hoxb-8 gene as well.
已证明Hox基因在沿胚胎前后（A-P）轴建立细胞的位置身份方面发挥着重要作用。研究这些基因的调控是阐明胚胎发育过程中区域化分子基础的第一步。我们在此报告对控制Hoxb-7（Hox-2.3）基因表达的顺式作用元件的鉴定。我们表明，驱动A-P限制基因表达的元件位于Hoxb-7基因3.5 kb近端上游序列内。缺失分析为Hoxb-7上游至少三个顺式作用控制元件以及其中一些元件在产生A-P限制转基因模式中的协同相互作用提供了证据。对一个元件进行了更详细的研究，该元件自身赋予转基因类似Hox的表达边界，发现其以方向和启动子依赖的方式起作用。Hoxb-7近端的3.5 kb序列共同介导了Hoxb-7/lacZ基因在一个区域内的A-P限制表达，该区域显示出比Hoxb-7更靠后的前端边界。对携带这些序列的转基因表达模式在整个胚胎发育过程中的演变进行了分析，结果表明除了初始表达略有延迟外，其模仿了内源基因的表达模式。我们得出结论，我们测试的转基因跨越总共27 kb的基因组序列，并未重现Hoxb-7表达模式的所有特征。Hoxb-7与转基因之间表达的差异可能揭示了Hox调控的一个方面，对此可能需要远距离顺式作用控制元件和/或基因成簇。在进化过程中可能有利于维持成簇组织的其他特征包括转录单位与相邻基因调控区域的部分重叠以及多个Hox基因之间的顺式调控相互作用：不仅Hoxb-7基因的顺式作用控制元件定位在Hoxb-8（Hox-2.4）基因的3'非翻译序列中，而且我们的实验表明Hoxb-7控制序列也调节Hoxb-8基因的表达。
