Pauli Thomas, Vedder Lucia, Dowling Daniel, Petersen Malte, Meusemann Karen, Donath Alexander, Peters Ralph S, Podsiadlowski Lars, Mayer Christoph, Liu Shanlin, Zhou Xin, Heger Peter, Wiehe Thomas, Hering Lars, Mayer Georg, Misof Bernhard, Niehuis Oliver
Center of Molecular Biodiversity Research, Zoological Research Museum Alexander Koenig, Adenauerallee 160, 51113, Bonn, Germany.
University of Tübingen, Geschwister-Scholl-Platz, 72074, Tübingen, Germany.
BMC Genomics. 2016 Nov 3;17(1):861. doi: 10.1186/s12864-016-3205-1.
Body plan development in multi-cellular organisms is largely determined by homeotic genes. Expression of homeotic genes, in turn, is partially regulated by insulator binding proteins (IBPs). While only a few enhancer blocking IBPs have been identified in vertebrates, the common fruit fly Drosophila melanogaster harbors at least twelve different enhancer blocking IBPs. We screened recently compiled insect transcriptomes from the 1KITE project and genomic and transcriptomic data from public databases, aiming to trace the origin of IBPs in insects and other arthropods.
Our study shows that the last common ancestor of insects (Hexapoda) already possessed a substantial number of IBPs. Specifically, of the known twelve insect IBPs, at least three (i.e., CP190, Su(Hw), and CTCF) already existed prior to the evolution of insects. Furthermore we found GAF orthologs in early branching insect orders, including Zygentoma (silverfish and firebrats) and Diplura (two-pronged bristletails). Mod(mdg4) is most likely a derived feature of Neoptera, while Pita is likely an evolutionary novelty of holometabolous insects. Zw5 appears to be restricted to schizophoran flies, whereas BEAF-32, ZIPIC and the Elba complex, are probably unique to the genus Drosophila. Selection models indicate that insect IBPs evolved under neutral or purifying selection.
Our results suggest that a substantial number of IBPs either pre-date the evolution of insects or evolved early during insect evolution. This suggests an evolutionary history of insulator binding proteins in insects different to that previously thought. Moreover, our study demonstrates the versatility of the 1KITE transcriptomic data for comparative analyses in insects and other arthropods.
多细胞生物的体型发育在很大程度上由同源异型基因决定。而同源异型基因的表达又部分受绝缘子结合蛋白（IBP）调控。虽然在脊椎动物中仅鉴定出少数几种增强子阻断IBP，但常见的果蝇（黑腹果蝇）至少有十二种不同的增强子阻断IBP。我们筛选了最近从1KITE项目汇编的昆虫转录组以及来自公共数据库的基因组和转录组数据，旨在追踪昆虫和其他节肢动物中IBP的起源。
我们的研究表明，昆虫（六足动物）的最后一个共同祖先已经拥有大量的IBP。具体而言，在已知的十二种昆虫IBP中，至少有三种（即CP190、Su(Hw)和CTCF）在昆虫进化之前就已经存在。此外，我们在早期分支的昆虫目，包括衣鱼目（衣鱼和石蛃）和双尾目（双尾虫）中发现了GAF直系同源物。Mod(mdg4)很可能是新翅类昆虫的衍生特征，而Pita可能是全变态昆虫的进化新特征。Zw5似乎仅限于裂翅果蝇，而BEAF-32、ZIPIC和Elba复合体可能是果蝇属特有的。选择模型表明，昆虫IBP在中性或纯化选择下进化。
我们的结果表明，大量的IBP要么在昆虫进化之前就已存在，要么在昆虫进化早期就已进化。这表明昆虫中绝缘子结合蛋白的进化历史与之前认为的不同。此外，我们的研究证明了1KITE转录组数据在昆虫和其他节肢动物比较分析中的多功能性。
