Nodal paralogues underlie distinct mechanisms for visceral left-right asymmetry in reptiles and mammals
Nodal paralogues underlie distinct mechanisms for visceral left-right asymmetry in reptiles and mammals
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DOI：
10.1038/s41559-019-1072-2
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发表时间：
2020-01-06
影响因子：
16.8
通讯作者：
Hamada, Hiroshi
中科院分区：
文献类型：
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作者：
Kajikawa, Eriko;Horo, Uzuki;Hamada, Hiroshi
脊椎动物的左右对称是在发育过程中通过不同的机制建立起来的，包括运动的纤毛。在这里，作者展示了两个没有活动纤毛的爬行动物胚胎的左右组织者的节旁链的不对称表达。在小鼠、青蛙和斑马鱼的早期胚胎发生过程中，由左右组织者（LRO）的运动纤毛产生的单向流体流动打破了左右对称。然而，鸡胚不需要活动纤毛来破坏L-R对称。脊椎动物中L-R对称破缺机制的多样性以及非哺乳动物羊膜动物中这种对称破缺的触发机制尚不清楚。本文研究了马达加斯加地壁虎和中国软壳龟两种爬行动物的L-R不对称是如何建立的。这两种爬行动物似乎都没有活动的纤毛。在爬行动物胚胎中，LRO上的节点基因的表达被发现是不对称的，这与依赖纤毛进行L-R模式的脊椎动物（如小鼠）形成鲜明对比。来源于古老基因重复的两个节点基因的同源基因在纤毛依赖和纤毛独立的脊椎动物中被保留和表达差异。这两个节点的表达在侧板中胚层受到类似的控制，但在LRO受到不同的调控。因此，我们对爬行动物胚胎的深入分析表明，哺乳动物和非哺乳动物羊膜动物采用不同的策略，依赖于不同的节点旁系，使LRO上的节点活动不对称。
Left-right symmetry in vertebrates is established during development by different mechanisms, including motile cilia. Here, the authors show asymmetric expression of a Nodal paralogue in the left-right organizer in two reptilian embryos, which do not have motile cilia.Unidirectional fluid flow generated by motile cilia at the left-right organizer (LRO) breaks left-right (L-R) symmetry during early embryogenesis in mouse, frog and zebrafish. The chick embryo, however, does not require motile cilia for L-R symmetry breaking. The diversity of mechanisms for L-R symmetry breaking among vertebrates and the trigger for such symmetry breaking in non-mammalian amniotes have remained unknown. Here we examined how L-R asymmetry is established in two reptiles, Madagascar ground gecko and Chinese softshell turtle. Both of these reptiles appear to lack motile cilia at the LRO. The expression of the Nodal gene at the LRO in the reptilian embryos was found to be asymmetric, in contrast to that in vertebrates such as mouse that are dependent on cilia for L-R patterning. Two paralogues of the Nodal gene derived from an ancient gene duplication are retained and expressed differentially in cilia-dependent and cilia-independent vertebrates. The expression of these two Nodal paralogues is similarly controlled in the lateral plate mesoderm but regulated differently at the LRO. Our in-depth analysis of reptilian embryos thus suggests that mammals and non-mammalian amniotes deploy distinct strategies dependent on different Nodal paralogues for rendering Nodal activity asymmetric at the LRO.