Li Song, Wang Guanjie, Liu Dahai, Liu Qiuming, Hu Guobin
College of Marine Life Sciences, Ocean University of China, Qingdao 266003, China; Institute of Evolution & Marine Biodiversity, Ocean University of China, Qingdao 266003, China.
First Institute of Oceanography, State Oceanic Administration of China, Qingdao 266061, China.
Dev Comp Immunol. 2017 Aug;73:163-168. doi: 10.1016/j.dci.2017.03.021. Epub 2017 Mar 27.
Toll-like receptor 21 (TLR21) is a non-mammalian TLR recognizing unmethylated CpG DNA and considered as a functional homolog of mammalian TLR9. In the present study, a TLR21 gene was cloned from turbot, Scophthalmus maximus, its immune responsive expression was subsequently studied in vivo. The turbot (Sm)TLR21 gene is an intronless gene with a length of 3527 bp and encodes a peptide of 984 amino acids. The deduced protein possesses a signal peptide sequence, a leucine-rich repeat (LRR) domain composed of 16 LRR motifs, a transmembrane (TM) region and a Toll/interleukin-1 receptor (TIR) domain. Phylogenetic analysis grouped it with other teleost TLR21s. Quantitative real-time PCR (qPCR) analysis demonstrated the constitutive expression of SmTLR21 mRNA in all twelve examined tissues with higher levels in the lymphomyeloid-rich tissues like spleen and head kidney. Further, upon stimulation with polyinosinic: polycytidylic acid [poly(I:C)], turbot reddish body iridovirus (TRBIV) and CpG oligodeoxynucleotides (CpG-ODN) 2395, the SmTLR21 mRNA expression was up-regulated in the gills, head kidney, spleen and muscle. The maximum increases of SmTLR21 transcript levels ranged from 1.3 to 8.1-fold and appeared at 3 h to 5 day post-injection depending on different organs and stimuli. These findings suggest that SmTLR21 may play an important role in the immune responses to the infections of a broad range of pathogens that include RNA and DNA viruses and bacteria.
Toll样受体21（TLR21）是一种非哺乳动物的TLR，可识别未甲基化的CpG DNA，被认为是哺乳动物TLR9的功能同源物。在本研究中，从大菱鲆（Scophthalmus maximus）中克隆了TLR21基因，随后在体内研究了其免疫反应性表达。大菱鲆（Sm）TLR21基因是一个无内含子的基因，长度为3527 bp，编码一个由984个氨基酸组成的肽。推导的蛋白质具有信号肽序列、由16个LRR基序组成的富含亮氨酸重复序列（LRR）结构域、跨膜（TM）区域和Toll/白细胞介素-1受体（TIR）结构域。系统发育分析将其与其他硬骨鱼TLR21归为一类。定量实时PCR（qPCR）分析表明，SmTLR21 mRNA在所有12个检测组织中均有组成性表达，在富含淋巴髓样组织如脾脏和头肾中的表达水平较高。此外，在用聚肌苷酸：聚胞苷酸[poly（I:C）]、大菱鲆红体虹彩病毒（TRBIV）和CpG寡脱氧核苷酸（CpG-ODN）2395刺激后，鳃、头肾、脾脏和肌肉中的SmTLR21 mRNA表达上调。SmTLR21转录水平的最大增加幅度为1.3至8.1倍，根据不同器官和刺激，在注射后3小时至5天出现。这些发现表明，SmTLR21可能在对包括RNA和DNA病毒以及细菌在内的多种病原体感染的免疫反应中发挥重要作用。
