家蚕免疫相关基因和信号途径的鉴定和比较分析

家蚕Bombyx mori是一种重要的经济昆虫, 在中国约有5 000年的驯化历史。家蚕分子免疫学方面的最新研究已经初步勾勒出其先天免疫的轮廓。本研究基于更新的家蚕基因组数据, 通过与黑腹果蝇Drosophila melanogaster、冈比亚按蚊Anopheles gambiae、意大利蜜蜂Apis mellifera和赤拟谷盗Tribolium castaneum基因组的比较分析, 鉴定了家蚕21个免疫相关基因家族的218个基因, 其编码产物包括模式识别受体、信号传导因子、效应分子和氧化防御相关的酶类。尽管信号传导因子的序列分化较大, 但系统进化分析显示它们在不同昆虫间呈明显的直系同源关系。相反, 与识别、调制和效应因子相关的基因的序列保守性更高, 但是这些基因家族明显缺乏直系同源基因, 由此推测这些基因是由物种特异的基因复制机制产生的。结果提示家蚕拥有与其他昆虫相同的免疫应答调控的分子机制, 而且家蚕同样可以通过基因复制及其序列分化等方式调节防御策略。

Identification and comparative analysis of immune-related genes and signaling pathways in the silkworm, Bombyx mori

The silkworm,Bombyx mori,has been a domesticated,economically important insect for 5 000 years.Recent accomplishments in molecular immunology have revealed just a preliminary outline for silkworm innate immunity.The acquisition of the updated silkworm genome has enabled a comparative analysis of the silkworm immune-related genes and signaling pathways.In this study,through comparing with the sequenced Drosophila melanogaster,Anopheles gambiae,Apis mellifera and Tribolium castaneum genomes,we identified over 218 genes in the silkworm that fall into 21 families involved in immune defense,including pattern recognition receptors,signaling transducers,effectors and oxidative defense enzymes.Phylogenetic analysis showed that the signal transducers have remarkable orthologous relationships between different insect species in spite of the divergent sequences.In contrast,gene families associated with recognition,modulation and effectors exhibit more significant sequence conservation.However,the orthologs of these families are remarkably absent,presumably attributable to the lineage-specific gene duplication.Our results suggest that common mechanisms may be responsible for innate-immunity responses to pathogens via signaling pathways in the silkworm.Furthermore,hosts may adjust their defensive strategies by gene duplication and sequence divergence to kill pathogens.