Axial Patterning and diversification in the Cnidaria predate the Hox system
Axial Patterning and diversification in the Cnidaria predate the Hox system
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DOI：
10.1016/j.cub.2006.03.036
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发表时间：
2006-05-09
期刊：
影响因子：
9.2
通讯作者：
Miller, David J.
中科院分区：
文献类型：
--
作者：
Kamm, Kai;Schierwater, Bernd;Miller, David J.
在动物界，Hox基因以集群的形式组织，其基因组组织反映了它们在前/后（A/P）轴上的核心作用[1-7]。虽然在双边动物的共同祖先中存在一组Hox基因，但这一系统的起源尚不清楚（参见b[8]）。根据两种与双胞门最接近的现存门的代表——Nematostella海葵和hydromedusa Eleutheria海葵的新数据，我们认为刺胞门早于Hox系统的进化。虽然类似Hox的基因存在于一系列刺胞动物中，但其中许多是相似的，并且在线虫属和刺线虫属中都没有Hox集群的存在。除了独立复制的基因外，刺胞动物的基因是不连锁的，在一些情况下，两侧有非hox基因。此外，刺胞动物基因的表达模式与Hox模式不一致。我们得出结论，刺胞门/两侧门的分裂发生在确定的Hox系统发展之前。现存刺胞动物在形态和发育特征上的惊人变化表明，在动物王国中Hox系统和形态多样性之间没有必然的联系，一个规范的Hox系统并不是轴向模式的强制要求。
Across the animal kingdom, Hox genes are organized in clusters whose genomic organization reflects their central roles in patterning along the anterior/posterior (A/P) axis [1-7]. While a cluster of Hox genes was present in the bilaterian common ancestor, the origins of this system remain unclear (cf. [8]). With new data for two representatives of the closest extant phylum to the Bilateria, the sea anemone Nematostella and the hydromedusa Eleutheria, we argue here that the Cnidaria predate the evolution of the Hox system. Although Hox-like genes are present in a range of cnidarians, many of these are paralogs and in neither Nematostella nor Eleutheria is an equivalent of the Hox cluster present. With the exception of independently duplicated genes, the cnidarian genes are unlinked and in several cases are flanked by non-Hox genes. Furthermore, the cnidarian genes are expressed in patterns that are inconsistent with the Hox paradigm. We conclude that the Cnidaria/Bilateria split occurred before a definitive Hox system developed. The spectacular variety in morphological and developmental characteristics shown by extant cnidarians demonstrates that there is no obligate link between the Hox system and morphological diversity in the animal kingdom and that a canonical Hox system is not mandatory for axial patterning.