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首页> 外文期刊>American Zoologist >Cnidarians reveal intermediate stages in the evolution of Hox clusters and axial complexity
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Cnidarians reveal intermediate stages in the evolution of Hox clusters and axial complexity

机译：鸟类学家揭示了Hox团簇进化和​​轴向复杂性的中间阶段

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Across major phylogenetic comparisons, the evolution of Hox clusters generally parallels the evolution of axial complexity. Sponges lack a fixed primary body axis and regional axial differentiation. Correspondingly, sponges appear to lack a Hox cluster. Bilaterian animals are characterized, at least primitively, by the presence of an anterior-posterior axis. In many bilaterians, the anterior-posterior axis is finely subdivided into morphologically distinct regions; e.g., consider the many distinct vertebrae of the human vertebral column or tile many distinct body segments of the fruitfly. This axial complexity is encoded in part, by the genes of the Hox cluster. Bilaterians possess from seven to upwards of forty Hox genes which sort into four monophyletic classes (anterior, group-3, central, and posterior). Cnidarians (e.g., sea anemones) display an intermediate stage of axial complexity. Unlike sponges, they possess a fixed primary body axis, known as the oral-aboral axis, with a distinct head, body column, and foot. However, the primary axis of cnidarians lacks the degree of axial differentiation found in vertebrates or insects. Cnidarians possess distinct anterior and posterior Hox genes. Cnidarians appear to lack group-3 or central Hox genes. Southern mapping experiments in the sea anemone, Nematostella indicate linkage between an anterior Hox gene, an even-skipped ortholog, and a posterior Hox gene. The linkage of eve to a Hox gene, a condition previously described in a coral, is found in vertebrates but apparently absent in insects. Cnidarians hold the potential to reveal important intermediate stages in the evolution of Hox clusters and axial complexity.
机译：在主要的系统发育比较中，Hox簇的演化通常与轴向复杂性的演化平行。海绵缺乏固定的主体轴和区域轴向差异。相应地，海绵似乎缺少Hox簇。双语动物的特征至少在最初就以前后轴的存在为特征。在许多双语者中，前后轴被细分为形态上不同的区域。例如，考虑人类椎骨的许多不同的椎骨或平铺果蝇的许多不同的身体部分。这种轴向复杂性部分地由Hox簇的基因编码。双语者拥有从7个到多达40个Hox基因，这些基因分为四个单系类别（前部，第3组，中央和后部）。念珠菌（例如海葵）处于轴向复杂性的中间阶段。与海绵不同，它们具有固定的主体轴（称为口腔轴线），并具有明显的头部，身体柱和脚。然而，刺胞的主轴缺乏在脊椎动物或昆虫中发现的轴向分化程度。笔者拥有独特的前后Hox基因。念珠菌似乎缺乏第3组或中央Hox基因。在海葵Nematostella中进行的Southern制图实验表明，前Hox基因，均匀跳过的直向同源物和后Hox基因之间存在关联。平安夜与以前在珊瑚中描述过的Hox基因的联系在脊椎动物中发现，但在昆虫中却不存在。猎人有潜力揭示Hox团簇的进化和轴向复杂性的重要中间阶段。

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