State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province 430072, China.
University of Chinese Academy of Sciences, Beijing 100049, China.
J Immunol. 2018 Dec 1;201(11):3329-3342. doi: 10.4049/jimmunol.1800553. Epub 2018 Nov 2.
In vertebrates, intron-containing and intronless type I IFN genes have recently been reported in amphibian model species and s. However, whether intronless type I IFNs in amphibians are the ancestral genes of type I IFNs in amniotes or just represent the independent divergence in amphibians is unknown or even uninvestigated. In this study, both intron-containing and intronless type I IFN genes, as well as their receptor genes, were identified in the Tibetan frog The evidence obtained from homology, synteny, phylogeny, and divergence time showed that intronless type I IFN genes in and in might have arisen from two independent retroposition events occurred in these two lineages, and the retrotransposition causing the generation of intronless type I IFN genes in amniotes is another independent event beyond the two in amphibians. It can then be proposed that intronless type I IFNs in and may not be the ancestral genes of intronless type I IFNs in amniotes but may just represent two independent bifurcations in the amphibian lineage. Furthermore, both intronless and intron-containing type I IFNs in showed strong ability in inducing the expression of IFN-stimulated genes and the strong antiviral activity against frog virus 3. The present study thus provides the evolutionary evidence to support the independent retroposition hypothesis for the occurrence of intronless type I IFN genes in amphibians and contributes to a functional understanding of type I IFNs in this group of vertebrates.
在脊椎动物中，最近在两栖动物模型物种[1]和[2]中报道了含有内含子和无内含子的 I 型 IFN 基因。然而，两栖动物中的无内含子 I 型 IFN 是羊膜动物中 I 型 IFN 的祖先基因，还是仅仅代表两栖动物中的独立分化，目前尚不清楚，甚至尚未研究。在这项研究中，在西藏青蛙[3]中鉴定了含有内含子和无内含子的 I 型 IFN 基因及其受体基因。同源性、基因同线性、系统发育和分歧时间的证据表明，[3]和[4]中的无内含子 I 型 IFN 基因可能是这两个谱系中两次独立反转录事件的结果，而导致羊膜动物中无内含子 I 型 IFN 基因产生的反转录事件是两栖动物中两次之外的另一个独立事件。因此，可以提出，[3]和[4]中的无内含子 I 型 IFN 可能不是羊膜动物中无内含子 I 型 IFN 的祖先基因，而可能只是两栖动物谱系中的两个独立分支。此外，[3]中的无内含子和含内含子的 I 型 IFN 都表现出强烈诱导 IFN 刺激基因表达和强烈抗蛙病毒 3 的抗病毒活性。本研究因此提供了进化证据，支持了两栖动物中无内含子 I 型 IFN 基因发生的独立反转录假说，并有助于对这一类脊椎动物中 I 型 IFN 的功能理解。
