Engineering Research Center of Ecology and Agricultural Use of Wetland (Ministry of Education), Yangtze University, Jingzhou, 434024, PR China; Guangxi Key Laboratory of Marine Biotechnology, Guangxi Institute of Oceanology, Beihai, 536006, PR China.
Engineering Research Center of Ecology and Agricultural Use of Wetland (Ministry of Education), Yangtze University, Jingzhou, 434024, PR China.
Fish Shellfish Immunol. 2019 Jan;84:572-586. doi: 10.1016/j.fsi.2018.10.055. Epub 2018 Oct 23.
The CXC chemokine receptors (CXCRs) play critical roles in innate and adaptive immune systems. In this study, six Asian swamp eel (Monopterus albus) CXCRs (MaCXCR1-4) were identified and their molecular characterization and expression patterns were analyzed. The open reading frames (ORFs) of MaCXCR1a, MaCXCR1b, MaCXCR2, MaCXCR3a, MaCXCR3b, and MaCXCR4 were 1074 bp (base pairs), 1080 bp, 1125 bp, 1146 bp, 1083 bp, and 1140 bp, and encoded proteins of 357 aa (amino acids), 359 aa, 374 aa, 381 aa, 360 aa, and 379 aa, respectively. All these CXCRs have seven conserved transmembrane domains and four cysteines (with the exception of MaCXCR3b). Multiple sequence alignment revealed that the MaCXCRs possess a typical G-protein receptor family 1 signature and a DRY motif. There are also one to four potential N-glycosylation sites in the extracellular regions of the MaCXCRs, mainly distributed in the N-terminus and extracellular hydrophilic loop (ECL) 2 region. Phylogenetic analysis demonstrated that the MaCXCRs were clustered together with homologous proteins from other fish. Taken together with the amino acid identity and similarity analysis, these results suggested that the MaCXCRs are conserved with other homologous genes, in which CXCR4 is more conserved than CXCR1-3. The MaCXCRs loci showed conserved synteny among teleost fish, and we found that human CXCR1 shares a common ancestor with fish CXCR1a. MaCXCRs were constitutively expressed in a wide range of tissues (especially in immune-related tissues) with different expression levels, suggesting that the MaCXCRs have different roles in un-stimulated tissues, and may play vital roles under normal conditions. MaCXCRs showed different fold changes in the spleen after Aeromonas veronii and polyinosinic-polycytidylic acid (poly I:C) challenge, which suggested that MaCXCR1a and MaCXCR3a have longer antiviral activities compared with their antibacterial functions, and that MaCXCR1b possesses stronger antiviral than antibacterial activity. MaCXCR4 may play vital roles during bacterial and viral infection; however, MaCXCR2 has relatively small effect in antibacterial and antiviral responses. The differential responses of these genes to bacteria and poly I:C implied the differences in the mechanisms of defense against viruses and bacteria.
CXC 趋化因子受体（CXCRs）在先天和适应性免疫系统中发挥着关键作用。本研究中，鉴定了 6 种亚洲鳗鲡（Monopterus albus）CXCRs（MaCXCR1-4），并分析了它们的分子特征和表达模式。MaCXCR1a、MaCXCR1b、MaCXCR2、MaCXCR3a、MaCXCR3b 和 MaCXCR4 的开放阅读框（ORFs）分别为 1074bp、1080bp、1125bp、1146bp、1083bp 和 1140bp，编码的蛋白质分别为 357aa、359aa、374aa、381aa、360aa 和 379aa。所有这些 CXCR 都具有七个保守的跨膜结构域和四个半胱氨酸（MaCXCR3b 除外）。多重序列比对显示，MaCXCRs 具有典型的 G 蛋白受体家族 1 特征和 DRY 基序。MaCXCRs 的细胞外区域还存在 1 到 4 个潜在的 N-糖基化位点，主要分布在 N 端和细胞外亲水环（ECL）2 区域。系统进化分析表明，MaCXCRs 与来自其他鱼类的同源蛋白聚集在一起。与氨基酸同源性和相似性分析相结合，这些结果表明，MaCXCRs 与其他同源基因一样保守，其中 CXCR4 比 CXCR1-3 更保守。MaCXCRs 基因座在硬骨鱼类中表现出保守的同线性，我们发现人类 CXCR1 与鱼类 CXCR1a 具有共同的祖先。MaCXCRs 在广泛的组织（尤其是免疫相关组织）中持续表达，表达水平不同，这表明 MaCXCRs 在未受刺激的组织中具有不同的作用，并且在正常情况下可能发挥重要作用。在鳗鲡受到鳗弧菌和聚肌胞（poly I:C）刺激后，MaCXCRs 在脾脏中的表达发生了不同的变化，这表明 MaCXCR1a 和 MaCXCR3a 具有比其抗菌功能更长的抗病毒活性，而 MaCXCR1b 具有比抗菌活性更强的抗病毒活性。MaCXCR4 可能在细菌和病毒感染过程中发挥重要作用；然而，MaCXCR2 在抗细菌和抗病毒反应中的作用相对较小。这些基因对细菌和 poly I:C 的不同反应表明，它们在防御病毒和细菌方面的机制存在差异。
