mRNA m6A methylation in wood frog brain is maintained during freezing and anoxia

Abstract

Freeze tolerance is an adaptive strategy that wood frogs (Rana sylvatica) use to survive the subzero temperatures of winter. It is characterized by a variety of metabolic and physiological changes that facilitate successful freezing and anoxia. As both mRNA regulation and posttranslation protein modification have been implicated in freeze tolerance, we hypothesized that posttranslational RNA regulation is also involved in coordinating freeze-thaw cycles and metabolic rate depression. As such, we investigated the most abundant RNA modification, adenosine methylation (N6-methyladenosine; m6A) in wood frog brains during 24 h periods of freezing and anoxia. This was followed by an examination of levels of RNA methyltransferases, demethyltransferases, and the readers of RNA methylation. Despite relative levels of methylation on mRNA remaining constant throughout freezing and anoxia, a significant increase in relative abundance of m6A methyltransferases METTL3 and METTL14 was observed. In addition, we investigated the effect of m6A RNA methylation on mRNA triaging to stress granules and report a significant increase in stress granule markers TIAR and TIA-1 in both freezing and anoxia. Our findings are the first report of RNA posttranslational regulation during metabolic rate depression in the wood frog brain and suggest that the dynamic RNA methylation observed is not directly linked to mRNA regulation during periods of extreme metabolic reorganization, warranting future investigations.