Evolution, divergence and loss of the Nodal signalling pathway: new data and a synthesis across the Bilateria
Evolution, divergence and loss of the Nodal signalling pathway: new data and a synthesis across the Bilateria
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DOI：
10.1387/ijdb.140133cg
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发表时间：
2014-01-01
影响因子：
0.7
通讯作者：
Hejnol, Andreas
中科院分区：
文献类型：
--
作者：
Grande, Cristina;Maria Martin-Duran, Jose;Hejnol, Andreas
自从发现 TGF-β 信号分子 Nodal 及其下游效应子 Pitx 在软体动物和后口动物之间建立不对称性方面具有平行作用以来，关于该信号通路在整个两侧对称动物中的保守程度的争论一直在持续。进一步的分类单元采样对于了解动物中这一信号通路的进化和分歧至关重要。通过基因组和转录组挖掘，我们证实了 nodal 和 Pitx 在一系列其他动物类群中的存在，但它们的存在尚未被描述。原位杂交用于显示这些基因在腕足动物和涡虫中的胚胎表达。我们发现，nodal 和 Pitx 基因在螺旋纲中广泛保守，并且 nodal 很可能在 Acoelomorpha 分化后出现在双边对称茎谱系中。此外，在腕足动物横向中，节点和 Pitx mRNA 似乎都以不对称方式表达。在检查的非后口动物基因组资源中没有发现左撇子直向同源物存在的证据。 Nodal 表达在许多螺旋谱系中是不对称的，表明 Nodal/Pitx 级联在两侧对称动物中建立不对称性可能具有祖先作用。
Since the discovery that the TGF-beta signalling molecule Nodal and its downstream effector Pitx have a parallel role in establishing asymmetry between molluscs and deuterostomes the debate over the degree to which this signalling pathway is conserved across the Bilateria as a whole has been ongoing. Further taxon sampling is critical to understand the evolution and divergence of this signalling pathway in animals. Using genome and transcriptome mining we confirmed the presence of nodal and Pitx in a range of additional animal taxa for which their presence has not yet been described. In situ hybridization was used to show the embryonic expression of these genes in brachiopods and planarians. We show that both nodal and Pitx genes are broadly conserved across the Spiralia, and nodal likely appeared in the Bilaterian stem lineage after the divergence of the Acoelomorpha. Furthermore, both nodal and Pitx mRNA appears to be expressed in an asymmetric fashion in the brachiopod Terebratalia transverse. No evidence for the presence of a Lefty ortholog could be found in the non-deuterostome genomic resources examined. Nodal expression is asymmetric in a number of spiralian lineages, indicating a possible ancestral role of the Nodal/Pitx cascade in the establishment of asymmetries across the Bilateria.