Probing the Physiological Role of RNA A-to-I Editing–Regulation of Editing Frequency by Heat Shock

• Main Authors: Hong-Ming Wang, 王鴻銘
• Other Authors: Hurng-Wern, Huang
• Format: Others
• Language: zh-TW
• Published: 2008
• Online Access: http://ndltd.ncl.edu.tw/handle/kdcs8r

碩士 === 國立中山大學 === 生物醫學研究所 === 96 === RNA editing had been considered as a rare exception to the central dogma of molecular biology in which the mRNA truthfully carries genetic code from nucleus to the ribosome for translation. However, researches in the last five years have revealed numerous, widespread RNA A-to-I editing sites in human genome. Although the effects of these editing events require further study, this finding strongly suggests RNA editing occurs frequently, and affects large number of genes. By selectively modifying a few sequences of a gene, RNA editing allows a cell to produce a population of proteins with different properties from a single gene. The major question of this thesis study is whether such editing event is actually dynamically regulated when the cellular physiological processes have to be adjusted in response to changing environment. A previous study screening for Drosophila mutants defected in hypoxia and heat tolerance discovered a hypnos-2 mutant strain which was later found to be defective in dADAR, the drosophila gene encoding the A-to-I editing enzyme, supporting the hypothesis that cells/organisms response to stressful environment by dADAR-mediated RNA editing. Two directions are used to approach how Drosophila uses A-to-I editing to adapt “heat” environment stress. First, whether the expression pattern of dADAR changes after heat shock was investegated. The result showed the dADAR gene exon 7 self-editing frequency was decreased by heat shock, thus possibly enhances dADAR activity after heat shock processing. Moreover it is worth noting that the isoform without -1 exon transcript were obviously up-regulated, and transcript with -1 sequence is relatively down-regulated. On the other hand, no significant changes in the dADAR mRNA expression levels and in the degrees of two dADAR promoters activity were observed. Second, the changes of editing frequency of 30 known A-to-I editing sites were investigated. Generally the editing frequency of majority editing sites changed after heat shock. Therefore, the dADAR activity, the dADAR gene transcript expression alternations, and A-to-I editing frequency of dADAR target genes did change after heat shock, supporting the notion that change of RNA editing pattern is a mechanism for organism to adapt to drastic environmental change. However, how the edited protein isoforms contribute to heat resistance requires further investigation.