title: Intronless and intron-containing type I IFN genes coexist in amphibian Xenopus tropicalis: Insights into the origin and evolution of type I IFNs in vertebrates.
abstract: Type I IFNs are considered to be the core IFN species in vertebrates because of their predominant antiviral effects. But, a puzzling question remains to be answered, as to how intronless type I IFN genes in amniotes might have evolved from intron-containing type I IFN genes in fish and amphibians. In this study, intronless and intron-containing type I IFNs were found in the amphibian model, Xenopus tropicalis, with a total of sixteen and five genes, respectively. The intronless IFNs can be divided into three subgroups, and the intron-containing ones into two subgroups, implying that a retroposition event might have occurred in amphibians, resulting in the generation of intronless type I IFN genes. Two models were tentatively proposed to explain the evolution of type I IFNs in vertebrates: in model A, fish should possess the most primitive multi-exon-containing type I IFNs, and intronless type I IFN genes in amphibians are the ancestor of modern intronless type I IFNs in amniotes; in model B, intronless type I IFN genes in X. tropicalis may just represent an independent bifurcation in this species or probably in amphibians, and intronless type I IFN genes in amniotes may have arisen from another retroposition event occurred in a transition period even when reptiles were diverged from amphibians. It is considered that the model B can reflect the current knowledge on the occurrence of intronless and intron-containing type I IFN genes in vertebrate lineages. This study thus contributes to a better understanding of the origin and evolution of type I IFNs in vertebrates, and of the occurrence of intronless I IFNs in higher vertebrates.
authors: 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.
authors: Zhen
authors: Z
authors: Gan
authors: State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province, 430072, China.
authors: Shan Nan
authors: SN
authors: Chen
authors: College of Fisheries, Jimei University, Xiamen, Fujian Province, 361021, China.
authors: Bei
authors: B
authors: Huang
authors: 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.
authors: Jing
authors: J
authors: Hou
authors: State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan, Hubei Province, 430072, China. Electronic address: pinnie@ihb.ac.cn.
authors: Pin
authors: P
authors: Nie
mesh_terms: D029845:Amphibian Proteins / Q000235:genetics*; D000818:Animals; D005075:Biological Evolution; D019143:Evolution, Molecular; D007370:Interferon Type I / Q000235:genetics*; D007438:Introns / Q000235:genetics*; D008954:Models, Biological; D010802:Phylogeny; D011995:Recombination, Genetic; D018626:Retroelements / Q000235:genetics; D059467:Transcriptome; D014981:Xenopus / Q000235:genetics* / Q000276:immunology*
chemical_list: D029845:Amphibian Proteins; D007370:Interferon Type I; D018626:Retroelements
keywords: Intron-containing type I IFN; Intronless type I IFN; Retroposition event; Type I IFN; Xenopus tropicalis