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首页> 外文期刊>EvoDevo >Nuclear receptors from the ctenophore Mnemiopsis leidyi lack a zinc-finger DNA-binding domain: lineage-specific loss or ancestral condition in the emergence of the nuclear receptor superfamily?
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Nuclear receptors from the ctenophore Mnemiopsis leidyi lack a zinc-finger DNA-binding domain: lineage-specific loss or ancestral condition in the emergence of the nuclear receptor superfamily?

机译：来自ten虫Mnemiopsis leidyi的核受体缺乏锌指DNA结合结构域：核受体超家族的出现会产生谱系特异性损失或祖先条件？

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Background Nuclear receptors (NRs) are an ancient superfamily of metazoan transcription factors that play critical roles in regulation of reproduction, development, and energetic homeostasis. Although the evolutionary relationships among NRs are well-described in two prominent clades of animals (deuterostomes and protostomes), comparatively little information has been reported on the diversity of NRs in early diverging metazoans. Here, we identified NRs from the phylum Ctenophora and used a phylogenomic approach to explore the emergence of the NR superfamily in the animal kingdom. In addition, to gain insight into conserved or novel functions, we examined NR expression during ctenophore development. Results We report the first described NRs from the phylum Ctenophora: two from Mnemiopsis leidyi and one from Pleurobrachia pileus. All ctenophore NRs contained a ligand-binding domain and grouped with NRs from the subfamily NR2A (HNF4). Surprisingly, all the ctenophore NRs lacked the highly conserved DNA-binding domain (DBD). NRs from Mnemiopsis were expressed in different regions of developing ctenophores. One was broadly expressed in the endoderm during gastrulation. The second was initially expressed in the ectoderm during gastrulation, in regions corresponding to the future tentacles; subsequent expression was restricted to the apical organ. Phylogenetic analyses of NRs from ctenophores, sponges, cnidarians, and a placozoan support the hypothesis that expansion of the superfamily occurred in a step-wise fashion, with initial radiations in NR family 2, followed by representatives of NR families 3, 6, and 1/4 originating prior to the appearance of the bilaterian ancestor. Conclusions Our study provides the first description of NRs from ctenophores, including the full complement from Mnemiopsis. Ctenophores have the least diverse NR complement of any animal phylum with representatives that cluster with only one subfamily (NR2A). Ctenophores and sponges have a similarly restricted NR complement supporting the hypothesis that the original NR was HNF4-like and that these lineages are the first two branches from the animal tree. The absence of a zinc-finger DNA-binding domain in the two ctenophore species suggests two hypotheses: this domain may have been secondarily lost within the ctenophore lineage or, if ctenophores are the first branch off the animal tree, the original NR may have lacked the canonical DBD. Phylogenomic analyses and categorization of NRs from all four early diverging animal phyla compared with the complement from bilaterians suggest the rate of NR diversification prior to the cnidarian-bilaterian split was relatively modest, with independent radiations of several NR subfamilies within the cnidarian lineage.
机译：背景技术核受体（NRs）是一种古老的后生转录因子超家族，在调节生殖，发育和能量稳态方面起着至关重要的作用。尽管NRs之间的进化关系在两个著名的动物进化支（氘化口和原生动物）中得到了很好的描述，但是关于早期分离后生动物中NRs多样性的信息报道相对较少。在这里，我们从Ctenophora门中鉴定了NR，并使用了一种植物学方法来探讨NR超家族在动物界的出现。此外，为了深入了解保守或新颖的功能，我们检查了ten突发育过程中的NR表达。结果我们报告了最早描述的Ctenophora门的NRs：两个来自Mnemiopsis leidyi，另一个来自Pleurobrachiapilus。所有的tentenore NRs包含一个配体结合域，并与来自亚家族NR2A（HNF4）的NRs分组。出人意料的是，所有的tentenore NRs缺乏高度保守的DNA结合域（DBD）。 Mnemiopsis的NRs在发育中的尾足动物的不同区域表达。在胃胚形成过程中在内胚层中广泛表达一种。第二种表达最初是在胃胚形成期间在外胚层中，对应于未来触角的区域表达的。随后的表达仅限于顶端器官。对始尾藻，海绵，刺胞动物和原生动物的NR进行系统发育分析，支持以下假设：超家族的扩展是以逐步的方式发生的，首先是NR系列2的辐射，然后是NR系列3、6和1的代表。 / 4在出现双边祖先之前起源。结论我们的研究首次提供了拟南芥的NRs，包括来自Mnemiopsis的完整补体。在所有动物门中，Ctenophores的NR补体种类最少，其代表仅聚集一个亚科（NR2A）。 Ctenophores和海绵具有类似的限制性NR补体，支持以下假设：原始NR是类似HNF4的，并且这些谱系是动物树的前两个分支。在两个石oph科物种中缺少锌指DNA结合结构域表明了两个假说：该结构域可能已在石oph科世系中第二次丢失，或者，如果象鼻虫是动物树的第一个分支，则可能缺少原始的NR规范的DBD。对所有四个早期发散的动物门的NRs的系统生物学分析和分类与双边生物体的补语相比，表明在CNIDIAN-BILITIAN分裂之前，NR的多样化率相对较低，在CNIDIAN谱系中有几个NR亚族的独立辐射。

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