人類環型核醣核酸之偵測及其生理功能之探討

Abstract

環型核醣核酸(circRNA)是一種在結構上頭尾相連的核醣核酸序列，過去學界普遍認為在哺乳類細胞中不具功能，同時含量稀少。然而，近年由於次世代定序技術之發展，使得以高通量定序檢視細胞中表現出來之大部分核醣核酸之實驗(RNA-seq) 成為可能。致使近年多樣研究中所提供證據顯示，環型核醣核酸在人類與及哺乳類動物細胞中普遍存在，同時其中數個個案於後轉錄機制中扮演著調控腳色，已經獲得證實。這項證據顯示，此類環型核醣酸之作用為天然的微型核醣核酸海綿體(sponge)，具有吸取細胞中微型核醣核酸之功能。有鑑於此種分子結構之重要性，學生首先建構了公共資料庫，以便收集各國實驗研究所報告之環型核醣核酸。並且，從過去已發表公佈之定序實驗中，重新確認了新的環型核醣核酸之存在。另外，利用雙聚類分析的演算方法，從這些收集而來的資料中，微型核醣核酸了人類組織中個別表現之特殊環型核醣核酸。同時，也利用短片斷續列主體分析，配合雙聚類分析，探討了核醣核酸結合型蛋白，與環型核醣核酸之生成機制的關聯性。最後，經由這些分析的結果，學生發現了在七千多種人類基因中，存在一種特殊現象：在這些基因的序列中所產生的環型核醣核酸，會作為海綿體，調控某些微型核醣核酸之表現，而這些受到調控的微型核醣核酸，又已經在過去的研究中被証實過，會調控作為環型核醣核酸之根源的基因。學生發現此調控機制於人類體內存在。因其於基因調控上有如吞食自身的啣尾蛇一般，故稱此現象為環型核醣核酸中之「噬身之蛇型競爭內生調控迴圈」。

Emerging evidence indicates that Circular RNAs (circRNAs) exert post-transcriptional regulation of gene expression. A subclass of circRNA was found enriched with miRNA target sites. This evidence suggest that this kind of circRNA functions as natural miRNA sponge. Noticing the potential impacts of circular RNA research, a database was developed. In this database, CircNet, reported circRNAs and provide information of putative circRNA-miRNA interaction were collected. Meanwhile, novel circRNAs through retroactive sourced samples were identified. The correlation of RNA binding protein and circRNA was further explored through motif analysis and biclustering. Tissue specific expression profiling of circRNAs was also conducted. Finally, through these analysis, in 7,025 genes, putatively circRNA sponged miRNA had been experimentally verified targeting circRNA host gene were found. From this observation, the existence of the competitive endogenous relationship of circRNAs and miRNAs targeting their host genes can be observed. Given the self-regulation and self-induction nature of these circRNAs, this kind of phenomenon was hereby called Ouroboros Resembling Competitive Endogenous Loop (ORCEL) in circular RNAs.