Janssen Ralf, Damen Wim G M
Institute for Genetics, Evolutionary Genetics, University of Cologne, Zülpicher Strasse 47, 50674 Köln, Germany.
Evol Dev. 2008 Mar-Apr;10(2):155-65. doi: 10.1111/j.1525-142X.2008.00223.x.
Heart development exhibits some striking similarities between vertebrates and arthropods, for example in both cases the heart develops as a linear tube from mesodermal cells. Furthermore, the underlying molecular pathways exhibit a significant number of similarities between vertebrates and the fruit fly Drosophila, suggesting a common origin of heart development in the last common ancestor of flies and vertebrates. However, there is hardly any molecular data from other animals. Here we show that many of the key genes are also active in heart development in the spider Cupiennius salei. Spiders belong to the chelicerates and are distantly related to insects with respect to the other arthropods. The tinman/Nkx2.5 ortholog is the first gene to be specifically expressed in the presumptive spider heart, like in flies and vertebrates. We also show that tinman is expressed in a similar way in the beetle Tribolium castaneum. Taken together this demonstrates that tinman has a conserved role in the specification of the arthropod heart. In addition, we analyzed the expression of other heart genes (decapentaplegic, Wnt5, H15, even-skipped, and Mef2 ) in Cupiennius. The expression of these genes suggests that the genetic pathway of heart development may be largely conserved among arthropods. However, a major difference is seen in the earlier expression of the even-skipped gene in the developing spider heart compared with Drosophila, implying that the role of even-skipped in heart formation might have changed during arthropod evolution. The most striking finding, however, is that in addition to the dorsal tissue of the fourth walking leg segment and the opisthosomal segments, we discovered tinman-expressing cells that arise from a position dorsal to the cephalic lobe and that contribute to the anterior dorsal vessel. In contrast to the posterior heart tissue, these cells do not express the other heart genes. The spider heart thus is composed of two distinct populations of cells.
心脏发育在脊椎动物和节肢动物之间展现出一些显著的相似性，例如在这两种情况下，心脏都是从中胚层细胞发育成一条线性管道。此外，脊椎动物和果蝇之间潜在的分子途径存在大量相似之处，这表明在苍蝇和脊椎动物的最后一个共同祖先中，心脏发育有着共同的起源。然而，几乎没有来自其他动物的分子数据。在此我们表明，许多关键基因在蜘蛛栉足蛛的心脏发育中也具有活性。蜘蛛属于螯肢动物，与其他节肢动物中的昆虫亲缘关系较远。tinman/Nkx2.5直系同源基因是第一个在假定的蜘蛛心脏中特异性表达的基因，就像在苍蝇和脊椎动物中一样。我们还表明，tinman在甲虫赤拟谷盗中以类似的方式表达。综上所述，这表明tinman在节肢动物心脏的特化过程中具有保守作用。此外，我们分析了栉足蛛中其他心脏基因（果蝇的decapentaplegic、Wnt5、H15、even-skipped和Mef2）的表达。这些基因的表达表明，心脏发育的遗传途径在节肢动物中可能在很大程度上是保守的。然而，与果蝇相比，even-skipped基因在发育中的蜘蛛心脏中更早表达，这意味着even-skipped在心脏形成中的作用可能在节肢动物进化过程中发生了变化。然而，最惊人的发现是，除了第四步行腿节段和腹部节段的背侧组织外，我们发现了tinman表达细胞，这些细胞起源于头叶背侧的一个位置，并对前背血管有贡献。与心脏后部组织不同，这些细胞不表达其他心脏基因。因此蜘蛛心脏由两个不同的细胞群体组成。
