SHM对山羊免疫球蛋白重链表达多样性的影响研究

Somatic Hypermutation Diversity in the Goat Immunoglobulin Heavy Chain Variable Region Repertoire

山羊是重要家畜之一,目前关于其免疫球蛋白基因座的结构和表达多样性机制研究还较少。以西农萨能奶山羊为对象,通过体外克隆其免疫球蛋白重链重组的可变区并与潜在功能胚系基因比对,探究体细胞高突变在山羊免疫球蛋白重链可变区基因表达中的作用和机制。结果表明:山羊免疫球蛋白重链可变区表达过程中体细胞高突变的主要表现形式为碱基突变,插入/缺失突变较少。碱基替换突变偏好发生在A和G碱基,突变频率以A→G最高,其次为G→A和C→T;碱基发生转换的频率高于颠换,嘌呤碱基替换的数目是嘧啶的2倍左右;多数碱基替换发生在体细胞高突变的第二阶段,碱基改变集中在A:T碱基对上。碱基替换突变在可变区不同区域的替换频数表现为CDR2高于CDR1,FR3高于FR1和FR2。碱基的插入/缺失突变主要发生在CDRs,插入/缺失的碱基数目多为3或者3的倍数。总之,山羊免疫球蛋白重链可变区基因在表达过程中存在较为丰富的碱基突变,体细胞高突变是其重链可变区表达谱多样化的重要机制。

Goat is one of the most important livestock animals. Limited knowledge of goat immunoglobulin gene locus structure and expression diversity mechanisms is available. This study focused on the role of somatic hypermutation diversity mechanism in Xinong Saanen Dairy Goat. Based on the recently released goat genome data, the cDNA sequences of rearranged immunoglobulin heavy chain variable region were cloned in vitro and aligned with the potentially functional germline genes. Results showed that goat immunoglobulin heavy chain variable region genes had more preference to process base substitutions than insertion/deletion mutations. The base substitutions preferred occurring in A and G bases. A-to-G tran- stions were the most mutation point and followed by G-to-A and C-to-T. The bases biased for transitions over transversions in rearranged variable region. Substitutions in purnines were two times higher than pyrimidines. Most base mutations took place in the phase two of smatic hypermutation. The mutations located in CDR2 and FR3 were obviously more than the other immunoglobulin domains. A higher frequency of insertions/deletions was found in CDRs with three or multiples of three bases. In conclusion, relatively rich base mutations happened in the process of goat immunoglobulin heavy chain variable region gene expression. The somatic hypermutation was an immportant mechanism contributing to diversify the goat immunoglobulin heavy chain repertoire.