Abstract:
RNA editing alters mRNA sequence and contributes to transcriptome diversity. Because only a handful of functional RNA-editing cases are known, it is debated whether most RNA editing observed is beneficial. Recent studies in squid and octopus reported an unusually large number of A to I editing events, many of which are nonsynonymous and have high editing levels. Such a large dataset provides an opportunity to address the aforementioned debate. We calculated the fraction of sites edited and the median editing level for synonymous editing and non-synonymous editing, respectively. In squid, although the fraction of sites edited is smaller for nonsynonymous editing than for synonymous editing, the median editing level is greater for the former than for the latter. When our analysis is limited to high editing levels (>50%), the fraction of sites edited becomes significantly greater for nonsynonymous editing than synonymous editing. In octopus, both the fraction of sites edited and the median editing level are greater for nonsynonymous editing than for synonymous editing. These patterns suggest adaptive RNA editing at the genomic scale in squid and octopus, but contrast previous findings in humans. We are searching for the potential benefit of widespread RNA editing in cephalopods and studying the evolutionary origin of this phenomenon.