基于miRNA的演化研究昆虫的起源和早期分化

昆虫的起源和早期分化问题一直悬而未决，形态学和分子系统学研究对六足动物原尾纲、弹尾纲、双尾纲与昆虫纲的亲缘关系争论不休，对昆虫早期无翅类（石蛃和衣鱼）和古翅类（蜉蝣和蜻蜓）的分化历程也难以解析。由于新的miRNA家族在物种分化中不断获得，保守的miRNA家族很少二次丢失，miRNA几乎不会趋同演化，且成熟序列高度保守，因此从miRNA演化的角度探讨进化问题是新的突破点。本研究拟选取六足动物以及其它节肢动物代表类群，深度测序small RNA，结合已有基因组信息，注释每个类群的miRNA，发现已知的miRNA，并预测新的miRNA，分析miRNA家族在节肢动物中的获得、丢失和复制，miRNA cluster的演化和miRNA前体序列的变异，揭示六足动物miRNA的演化规律和类群特异miRNA的发生节点，求证使用miRNA研究六足动物系统发生的有效性，为昆虫的起源和早期分化提供全新的有力证据。

The origin and early split of insects are very important issues which remain still unclear. Based on morphological and molecular phylogenetic studies, the relationships of four hexapod groups (Protura, Collembola, Diplura and Insecta) are hotly debated, and the monophyly of wingless insects (Archaeognatha and Zygentoma), as well as the relationships between early winged insects (Ephemeroptera and Odonata) are difficult to determine. Exploring evolutionary questions from the perspective of miRNA evolution is a new breakthrough, because the novel miRNA families are continuously obtained during the species divergence, the conserved miRNA families are rarely lost secondarily, miRNAs are almost impossible to evolve convergently, and the mature miRNA sequences are highly conserved. By using high throughput deep sequencing of small RNAs (sRNA), and analyzing miRNA genes in known arthropod genomes, this study will establish the repertoire and evolutionary dynamics of miRNAs in the representative lineages of Protura, Collembola, Diplura and Insecta, as well as the representative taxa of other arthropods. By analyzing the gain and loss of miRNA families, the evolution of miRNA families and miRNA gene clusters, as well as the phylogenetic tree based on the miRNA precursor sequences in arthropods, the study aims to find the group-specific miRNAs, reveal the evolutionary pattern of miRNAs in hexapods, confirm the validity and reliability of miRNAs on the hexapod phylogeny, and provide brand new and robust evidences for the origin and early split of insects.