Sequence and Expression Analysis of Interferon Regulatory Factor 10 (IRF10) in Three Diverse Teleost Fish Reveals Its Role in Antiviral Defense

Background
Interferon regulatory factor (IRF) 10 was first found in birds and is present in the genome of other tetrapods (but not humans and mice), as well as in teleost fish. The functional role of IRF10 in vertebrate immunity is relatively unknown compared to IRF1-9. The target of this research was to clone and characterize the IRF10 genes in three economically important fish species that will facilitate future evaluation of this molecule in fish innate and adaptive immunity.
Molecular Characterization of IRF10 in Three Fish Species
In the present study, a single IRF10 gene was cloned in grass carp Ctenopharyngodon idella and Asian swamp eel Monopterus albus, and two, named IRF10a and IRF10b, in rainbow trout Oncorhynchus mykiss. The fish IRF10 molecules share highest identities to other vertebrate IRF10s, and have a well conserved DNA binding domain, IRF-associated domain, and an 8 exon/7 intron structure with conserved intron phase. The presence of an upstream ATG or open reading frame (ORF) in the 5’-untranslated region of different fish IRF10 cDNA sequences suggests potential regulation at the translational level, and this has been verified by in vitro transcription/translation experiments of the trout IRF10a cDNA, but would still need to be validated in fish cells.
Expression Analysis of IRF10 In Vivo and In Vitro
Both trout IRF10 paralogues are highly expressed in thymus, blood and spleen but are relatively low in head kidney and caudal kidney. Trout IRF10b expression is significantly higher than IRF10a in integumentary tissues i.e. gills, scales, skin, intestine, adipose fin and tail fins, suggesting that IRF10b may be more important in mucosal immunity. The expression of both trout IRF10 paralogues is up-regulated by recombinant IFN-γ. The expression of the IRF10 genes is highly induced by Poly I:C in vitro and in vivo, and by viral infection, but is less responsive to peptidoglycan and bacterial infection, suggesting an important role of fish IRF10 in antiviral defense.

Background
干扰素调节因子（Interferon regulatory factor, IRF）10最早在鸟类中被发现，存在于其他四足动物（但人类和小鼠除外）以及硬骨鱼的基因组中。相较于IRF1-9，IRF10在脊椎动物免疫中的功能作用尚不清楚。本研究的目标是在三种经济鱼类中克隆并鉴定IRF10基因，为后续评估该分子在鱼类先天免疫与适应性免疫中的功能提供研究基础。

Molecular Characterization of IRF10 in Three Fish Species
本研究中，我们从草鱼（Ctenopharyngodon idella）和亚洲沼泽鳗（Monopterus albus）中克隆得到单个IRF10基因，而在虹鳟（Oncorhynchus mykiss）中则克隆得到两个IRF10旁系同源基因，分别命名为IRF10a和IRF10b。鱼类IRF10分子与其他脊椎动物的IRF10同源性最高，且具备高度保守的DNA结合结构域、IRF相关结构域，以及具有保守内含子相位的8外显子/7内含子结构。不同鱼类IRF10 cDNA的5'非翻译区存在上游ATG起始密码子或开放阅读框（open reading frame, ORF），提示其存在翻译水平调控的潜力，该结论已通过虹鳟IRF10a cDNA的体外转录翻译实验得到验证，但仍需在鱼类细胞中进一步确认。

Expression Analysis of IRF10 In Vivo and In Vitro
两种虹鳟IRF10旁系同源基因均在胸腺、血液与脾脏中高表达，而在头肾和尾肾中表达量相对较低。在体被组织（即鳃、鳞片、皮肤、肠道、脂鳍与尾鳍）中，虹鳟IRF10b的表达量显著高于IRF10a，提示IRF10b可能在黏膜免疫中发挥更为关键的作用。两种虹鳟IRF10旁系同源基因的表达均可被重组干扰素-γ（recombinant IFN-γ）上调。IRF10基因的表达在体内外均可被聚肌胞苷酸（Poly I:C）与病毒感染显著诱导，但对肽聚糖和细菌感染的响应较弱，这表明鱼类IRF10在抗病毒防御中具有重要功能。