Pre-bilaterian origins of the Hox cluster and the Hox code: evidence from the sea anemone, Nematostella vectensis.
Pre-bilaterian origins of the Hox cluster and the Hox code: evidence from the sea anemone, Nematostella vectensis.
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DOI：
10.1371/journal.pone.0000153
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发表时间：
2007-01-24
期刊：
影响因子：
3.7
通讯作者：
Finnerty JR
中科院分区：
文献类型：
--
作者：
Ryan JF;Mazza ME;Pang K;Matus DQ;Baxevanis AD;Martindale MQ;Finnerty JR
Hox基因对两侧对称动物的许多形态创新至关重要。然而，早期的Hox进化仍然模糊不清。系统发育，发育和基因组分析的刺胞海葵Nematostella vectensis挑战最近声称，Hox代码是一个bilaterian发明，没有“真正的”Hox基因存在于刺胞门。系统发育分析的18个Hox相关基因从Nematostella确定推定的Hox 1，Hox 2，和Hox 9+基因。竞争假说之间的统计比较支持这些发现，包括明确考虑替代拓扑结构所隐含的基因损失。20个Hox相关基因的原位杂交研究表明，多个Hox基因表达在不同的区域沿着初级身体轴，支持存在一个前双侧Hox代码。此外，几个Hox基因表达的嵌套结构域沿着第二身体轴，表明在“背腹”图案的作用。一个簇的前部和后部的Hox基因，以及ParaHox基因簇进化之前的刺胞动物两侧分裂。有证据表明，这些集群是由一系列串联的基因复制事件形成的，并在双侧对称的共同祖先的初级和次级身体轴的模式中发挥了作用。刺胞动物和两侧动物在大约5.7亿至7亿年前有着共同的祖先，因此，它们都来自于共同的身体结构。我们的工作揭示了在这两个不同的谱系中发现的几个保守的遗传成分。这一发现与假设一致，即在刺胞动物和两侧动物的共同祖先中建立的一套发育规则今天仍然在起作用。
Hox genes were critical to many morphological innovations of bilaterian animals. However, early Hox evolution remains obscure. Phylogenetic, developmental, and genomic analyses on the cnidarian sea anemone Nematostella vectensis challenge recent claims that the Hox code is a bilaterian invention and that no “true” Hox genes exist in the phylum Cnidaria. Phylogenetic analyses of 18 Hox-related genes from Nematostella identify putative Hox1, Hox2, and Hox9+ genes. Statistical comparisons among competing hypotheses bolster these findings, including an explicit consideration of the gene losses implied by alternate topologies. In situ hybridization studies of 20 Hox-related genes reveal that multiple Hox genes are expressed in distinct regions along the primary body axis, supporting the existence of a pre-bilaterian Hox code. Additionally, several Hox genes are expressed in nested domains along the secondary body axis, suggesting a role in “dorsoventral” patterning. A cluster of anterior and posterior Hox genes, as well as ParaHox cluster of genes evolved prior to the cnidarian-bilaterian split. There is evidence to suggest that these clusters were formed from a series of tandem gene duplication events and played a role in patterning both the primary and secondary body axes in a bilaterally symmetrical common ancestor. Cnidarians and bilaterians shared a common ancestor some 570 to 700 million years ago, and as such, are derived from a common body plan. Our work reveals several conserved genetic components that are found in both of these diverse lineages. This finding is consistent with the hypothesis that a set of developmental rules established in the common ancestor of cnidarians and bilaterians is still at work today.
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