Wang Xifeng, Wang Peng, Wang Renping, Wang Chaolin, Bai Jianhui, Ke Cuncun, Yu Di, Li Kongpan, Ma Yonghe, Han Haitang, Zhao Yaofeng, Zhou Xin, Ren Liming
Beijing Advanced Innovation Center for Food Nutrition and Human Health, College of Food Science and Nutritional Engineering, China Agricultural University, Beijing, 100193, People's Republic of China.
State Key Laboratory of Agrobiotechnology, College of Biological Sciences, National Engineering Laboratory for Animal Breeding, China Agricultural University, Beijing, People's Republic of China.
Dev Comp Immunol. 2018 Aug;85:31-43. doi: 10.1016/j.dci.2018.01.009. Epub 2018 Mar 21.
All jawed vertebrates have four T cell receptor (TCR) chains that are expressed by thymus-derived lymphocytes and play a major role in animal immune defence. However, few studies have investigated the TCR chains of crocodilians compared with those of birds and mammals, despite their key evolutionary position linking amphibians, reptiles, birds and mammals. Here, employing an Alligator sinensis genomic bacterial artificial chromosome (BAC) library and available genome data, we characterized the genomic organization, evolution and expression of TRB and TRG loci in Alligator sinensis. According to the sequencing data, the Alligator sinensis TRB locus spans approximately 500 Kb of genomic DNA containing two D-J-C clusters and 43 V gene segments and is organized as Vβ-pJβ1-pCβ1-pDβ1-Dβ2- Jβ2-Cβ2-Vβ, whereas the TRG locus spans 115 Kb of DNA genomic sequence consisting of 18 V gene segments, nine J gene segments and one C gene segment and is organized in a classical translocon pattern as Vγ-Jγ-Cγ. Moreover, syntenic analysis of TRB and TRG chain loci suggested a high degree of conserved synteny in the genomic regions across mammals, birds and Alligator sinensis. By analysing the cloned TRB/TRG cDNA, we identified the usage pattern of V families in the expressed TRB and TRG. An analysis of the junctions of the recombined VJ revealed the presence of N and P nucleotides in both expressed TRB and TRG sequences. Phylogenetic analysis revealed that TRB and TRG loci possess distinct evolutionary patterns. Most Alligator sinensis V subgroups have closely related orthologues in chicken and duck, and a small number of Alligator sinensis V subgroups have orthologues in mammals, which supports the hypothesis that crocodiles are the closest relatives of birds and mammals. Collectively, these data provide insights into TCR gene evolution in vertebrates and improve our understanding of the Alligator sinensis immune system.
所有有颌脊椎动物都有四条T细胞受体（TCR）链，由胸腺来源的淋巴细胞表达，并在动物免疫防御中发挥主要作用。然而，与鸟类和哺乳动物相比，对鳄鱼TCR链的研究较少，尽管它们在连接两栖动物、爬行动物、鸟类和哺乳动物方面具有关键的进化地位。在这里，我们利用中华鳄基因组细菌人工染色体（BAC）文库和现有的基因组数据，对中华鳄TRB和TRG基因座的基因组组织、进化和表达进行了表征。根据测序数据，中华鳄TRB基因座跨越约500 Kb的基因组DNA，包含两个D-J-C簇和43个V基因片段，其组织形式为Vβ-pJβ1-pCβ1-pDβ1-Dβ2-Jβ2-Cβ2-Vβ，而TRG基因座跨越115 Kb的DNA基因组序列，由18个V基因片段九、个J基因片段和一个C基因片段组成，以经典的转座子模式组织为Vγ-Jγ-Cγ。此外，TRB和TRG链基因座的共线性分析表明，在哺乳动物、鸟类和中华鳄的基因组区域中存在高度保守的共线性。通过分析克隆的TRB/TRG cDNA，我们确定了表达的TRB和TRG中V家族的使用模式。对重组VJ连接处的分析表明，在表达的TRB和TRG序列中都存在N和P核苷酸。系统发育分析表明，TRB和TRG基因座具有不同的进化模式。大多数中华鳄V亚组在鸡和鸭中有密切相关的直系同源物，少数中华鳄V亚组在哺乳动物中有直系同源物，这支持了鳄鱼是鸟类和哺乳动物最亲近亲属的假设。总的来说，这些数据为脊椎动物TCR基因的进化提供了见解，并增进了我们对中华鳄免疫系统的理解。
