马氏珠母贝C1qDC基因家族成员的鉴定及表达分析

Identification and expression patterns of members of the C1qDC gene family in Pinctada fucata

含C1q结构域蛋白(C1q domain containing,C1qDC)是经典补体途径的起始分子,能够识别免疫复合物,启动补体系统经典途径。本研究基于马氏珠母贝(Pinctada fucata)全基因组测序数据,结合生物信息学方法对C1qDC基因进行了鉴定,同时对其系统进化关系、序列结构、基序组成、染色体定位和基因家族成员的表达水平进行了分析。结果显示,从马氏珠母贝全基因组数据中共鉴定出285个C1qDC基因;根据系统进化关系聚集为5个亚类,不均匀分布在14条染色体上;所有C1qDC序列均含有保守基序1。比较转录组数据分析显示,在溶藻弧菌(Vibrio alginolyticus)攻毒4 h后,马氏珠母贝C1qDC基因家族中有56个基因在血细胞中的表达水平发生了显著变化。其中,上调表达基因32个,下调表达基因24个。实时荧光定量PCR检测结果表明,随机挑选的8个C1qDC基因的表达模式与转录组数据一致。本研究结果为进一步解析马氏珠母贝C1qDC基因的进化模式及其在贝类免疫应答中的调控作用提供了理论基础。

The complement system is an evolutionary and crucial component of the innate immune response,which is key to detecting and removing invading pathogens.C1q-domain-containing proteins(C1qDC),as the first subcomponent of the classical pathway in the complement system,can bind immune complexes and activate the classical pathway.Although recent advances in many species have reported the characterization and functional roles of C1qDC in innate immunity,systematic knowledge of C1qDC is still lacking in Pinctada fucata.In this study,the phylogenetic relationship,sequence structure,motif composition,chromosome location,and expression pattern of identified C1qDC genes from the sequencing data of the whole genome of P.fucata were analyzed.The results showed that 285 C1qDC genes were identified and divided into five groups.C1qDC genes have been studied in many species,but the transcript number varies greatly among different species.In previous studies,232,335,and 476 C1qDC genes were identified in Mytilus galloprovincialis,Crassostrea gigas,and Crassostrea virginica,respectively.The transcript numbers are far more than that of C1qDC genes in fish and humans,and this is likely related to the lack of adaptive immunity of invertebrates and a weak ability of bivalves to resist adverse external environment and pathogens.The massive gene family expansion has occurred in bivalve evolution and is also common in the bivalve genomes.Structure analysis revealed that all the C1qDC proteins of P.fucata contained motif 1 and were randomly distributed on 14 chromosomes.Additionally,68 pairs of tandem duplication and one pair of segmental duplication events were found.The higher synonymous substitution rate relative to the non-synonymous rate observed in P.fucata evoked C1qDC genes to evolve under purification selection.Some C1qDC genes showed high levels of polymorphism and were driven by selective pressure to fight off the noxious pathogens.Adaptive evolution of sequence polymorphism likely reflected the coevolution or interplay of host and pathogen.Recent research showed that C1qDC mainly functions as a pattern recognition receptor to mediate cell phagocytosis and agglutination via directly interacting with the receptor on the cell outer membrane.According to the transcriptome data,56 C1qDC genes(32 upregulated and 24 downregulated)were significantly differentially expressed after the Vibrio alginolyticus challenge.Additionally,real-time PCR was implemented for eight randomly selected C1qDC genes,and agreement was confirmed between the high-throughput sequencing and real-time PCR data.The expression of the C1qDC genes increased in the hemocytes of P.fucata,which indicated that C1qDC might be involved in the immune response related to V.alginolyticus infection.These results provide a theoretical basis for further analysis of the evolutionary pattern of the C1qDC genes and the regulatory roles in the immune response in bivalves.