疱疹病毒其微型核糖核酸演化

Abstract

微型核糖核酸含有約二十到三十個核苷酸，它於 1993 年線蟲發育研究中被 發現。往後十幾年間，它陸續的在其他有機體中被發現。微型核糖核酸可藉由與 目標訊息核糖核酸互補結合進而降解或抑制其轉譯。第一個病毒微型核糖核酸於 2004 年發現之後，許多種病毒也接著被發現有微型核糖核酸。先前研究指出病 毒會利用微型核糖核酸調控其本身與宿主基因表現以創造出有利的生存環境和 躲避宿主免疫系統追補。此外，另有親緣研究指出，病毒有部分基因是從宿主基 因體中補捉的。因此，合理地懷疑病毒的微型核糖核酸或許也是由這種方式得來。 為了回答這問題，我從微型核糖核酸資料庫(miRBase)收集所有病毒的微型核糖 核酸以及比較它們的位置，發現病毒的基因內容、同源基因排列和微型核糖核酸 位置有高度相似，不過微型核糖核酸數量和序列卻不儘相同。其理由可能是不同 病毒獨立地在利用宿主表現基因時，連帶由其身上取得微型核糖核酸；也有可能 是不同病毒由共祖那共同繼承微型核糖核酸之後隨機累積變異而成。為了釐清病 毒微型核糖核酸起源，更多的序列包含預測的微型核糖核酸都需要廣泛被收集分 析，而本研究則提供了在病毒微型核糖核酸演化上較新的分析方式和思考。

MicroRNA (miRNA), a small RNA containing only twenty to thirty nucleotides, was discovered in a developmental study of Caenorhabditis elegans in 1993. During the next decades, a lot of these small RNAs were found in many other organisms. By binding to their target messenger RNAs, miRNA could generate degradation or translational inhibition of their target sequences. The first viral miRNA was reported in 2004. Much research on the identification or function of miRNAs has been conducted in variety of viruses. One of these research findings is that viruses would use their miRNAs to regulate both viral and host gene expression. In this way, they could build a suitable environment and avoid the immune system in their hosts. Viral genes were proposed to originate from host genomes in previous phylogenetic studies of viruses. Hence, it is reasonable to speculate that viruses might obtain their miRNAs in the same way. To answer this question, I collected all viral miRNAs on the experimental verified miRNA database (miRBase) and compared the locations of these miRNAs in the viral genomes. I found that two closely related viruses could have similar genome contents, gene order, and even the location of cluster of miRNAs. However, the number and sequences of the miRNAs in the two clusters are completely different. Two hypotheses were therefore proposed. First, different viruses captured different miRNAs independently from their hosts while they employing their hosts' gene expression machinery. Alternatively, these miRNAs could be generated by accumulating enormous nucleotide substitutions after the two viruses were diverged from their common ancestor. To verify these two hypotheses, more miRNAs sequences, including predicted data, should be collected and analyzed. This study may give an insight into viral evolution in host-virus interaction.