Intact cluster and chordate-like expression of ParaHox genes in a sea star.
Intact cluster and chordate-like expression of ParaHox genes in a sea star.
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DOI：
10.1186/1741-7007-11-68
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发表时间：
2013-06-27
期刊：
影响因子：
5.4
通讯作者：
Arnone MI
中科院分区：
文献类型：
--
作者：
Annunziata R;Martinez P;Arnone MI
ParaHox基因被认为是形成几个双边分类群肠道模式的主要角色。虽然这是这些转录因子发挥的基本作用，但它们的活性并不局限于内胚层，还延伸到外胚层和中胚层组织。ParaHox组由三个基因组成：GSX、XLOX和CDX。在一些分类群中(主要是脊索动物，但在某种程度上，在原口动物中也是如此)，这三个基因被排列成一个基因组簇，其方式类似于更知名的Hox基因。海胆拥有完整的ParaHox基因，但它们都分散在整个基因组中，这种排列可能代表了所有棘皮动物的原始状态。为了了解这组基因的进化史，我们克隆并鉴定了所有ParaHox基因，研究了它们的表达模式，并在棘皮动物早期分支类群的一个成员--小行星Patiria mini ata中确定了它们的基因组位置。我们在小型拟青霉基因组中鉴定了三个ParaHox同源基因。另两个PmLox和PmCDx在胚胎发育过程中表达，位于内胚层和外胚层的限制性结构域中。对Patiria细菌人工染色体(BAC)文库的筛选导致了包含这三个基因的克隆的鉴定。PmGsx和PmLox的转录方向与PmCDx基因在簇内的转录方向相反。对P.mini ata ParaHox基因的鉴定揭示了这样一个事实，即这些基因聚集在基因组中，与已报道的棘球藻类相反。由于在脊索动物和多毛类中分别报道了一个完整的簇或至少一个部分簇的存在，很明显，在棘皮动物中，海胆改变了原来的双边排列。此外，海星ParaHox的表达结构域显示出海胆中没有的脊索状特征，证实了在海胆中，随着进化时间的推移，各个基因的基因表达动态及其可能的调控相互作用已经明显改变。
The ParaHox genes are thought to be major players in patterning the gut of several bilaterian taxa. Though this is a fundamental role that these transcription factors play, their activities are not limited to the endoderm and extend to both ectodermal and mesodermal tissues. Three genes compose the ParaHox group: Gsx, Xlox and Cdx. In some taxa (mostly chordates but to some degree also in protostomes) the three genes are arranged into a genomic cluster, in a similar fashion to what has been shown for the better-known Hox genes. Sea urchins possess the full complement of ParaHox genes but they are all dispersed throughout the genome, an arrangement that, perhaps, represented the primitive condition for all echinoderms. In order to understand the evolutionary history of this group of genes we cloned and characterized all ParaHox genes, studied their expression patterns and identified their genomic loci in a member of an earlier branching group of echinoderms, the asteroid Patiria miniata. We identified the three ParaHox orthologs in the genome of P. miniata. While one of them, PmGsx is provided as maternal message, with no zygotic activation afterwards, the other two, PmLox and PmCdx are expressed during embryogenesis, within restricted domains of both endoderm and ectoderm. Screening of a Patiria bacterial artificial chromosome (BAC) library led to the identification of a clone containing the three genes. The transcriptional directions of PmGsx and PmLox are opposed to that of the PmCdx gene within the cluster. The identification of P. miniata ParaHox genes has revealed the fact that these genes are clustered in the genome, in contrast to what has been reported for echinoids. Since the presence of an intact cluster, or at least a partial cluster, has been reported in chordates and polychaetes respectively, it becomes clear that within echinoderms, sea urchins have modified the original bilaterian arrangement. Moreover, the sea star ParaHox domains of expression show chordate-like features not found in the sea urchin, confirming that the dynamics of gene expression for the respective genes and their putative regulatory interactions have clearly changed over evolutionary time within the echinoid lineage.
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