Damen W G, Tautz D
Zoologisches Institut der Universität München, Luisenstrasse 14, D-80333 München, Germany.
Dev Genes Evol. 1998 Dec;208(10):586-90. doi: 10.1007/s004270050218.
The class 3 Hox gene orthologue in insects, zerknüllt (zen), is not expressed along the anterior-posterior axis, but only in extra-embryonic tissues, suggesting that it has lost its function as a normal Hox gene. To analyse whether this loss of Hox gene function has already occurred in a basal arthropod lineage, we have isolated a Hox3 orthologue from the spider Cupiennius salei. In contrast to the insect zen sequences, which have a highly diverged homeobox, the spider Hox3 gene orthologue, Cs-Hox3, shows a high sequence similarity to the class 3 Hox genes of other phyla, including chordates. In situ hybridization in early embryos shows that it is expressed in a continuous region covering the pedipalp segment and the four leg-bearing segments. This expression pattern suggests a Hox-gene-like function for Cs-Hox3. On the other hand, the expression pattern does not strictly follow the colinearity rule, as it overlaps fully with the expression domain of the class 1 orthologue of the spider, Cs-lab. Still, our data suggest that the ancestor of the arthropods must have had a class 3 Hox gene with a function in anterior-posterior axis specification and that this function has been lost in the lineage leading to the insects.
昆虫中第3类同源异型基因直系同源物zerknüllt（zen）并非沿前后轴表达，而是仅在胚外组织中表达，这表明它已丧失作为正常同源异型基因的功能。为了分析同源异型基因功能的这种丧失是否已在基础节肢动物谱系中发生，我们从蜘蛛Cupiennius salei中分离出了一个Hox3直系同源物。与具有高度分化同源异型框的昆虫zen序列不同，蜘蛛Hox3基因直系同源物Cs - Hox3与包括脊索动物在内的其他门的第3类同源异型基因具有高度的序列相似性。早期胚胎的原位杂交显示，它在一个连续区域表达，该区域覆盖触肢节段和四个具腿节段。这种表达模式表明Cs - Hox3具有类似同源异型基因的功能。另一方面，这种表达模式并不严格遵循共线性规则，因为它与蜘蛛第1类直系同源物Cs - lab的表达域完全重叠。尽管如此，我们的数据表明节肢动物的祖先必定具有一个在前后轴特化中起作用的第3类同源异型基因，并且该功能在导致昆虫的谱系中已经丧失。
