The role of DNA methylation during anoxia tolerance in a freshwater turtle (Trachemys scripta elegans)

Abstract

Oxygen deprivation is a lethal stress that only a few animals can tolerate for extended periods. This study focuses on analyzing the role of DNA methylation in aiding natural anoxia tolerance in a champion vertebrate anaerobe, the red-eared slider turtle (Trachemys scripta elegans). We examined the relative expression and total enzymatic activity of four DNA methyltransferases (DNMT1, DNMT2, DNMT3a and DNMT3b), two methyl-binding domain proteins (MBD1 and MBD2), and relative genomic levels of 5-methylcytosine under control, 5 h anoxic, and 20 h anoxic conditions in liver, heart, and white skeletal muscle (n = 4, p < 0.05). In liver, protein expression of DNMT1, DNMT2, MBD1, and MBD2 rose significantly by two- to fourfold after 5 h anoxic submergence compared to normoxic-control conditions. In heart, 5 h anoxia submergence resulted in a 1.4-fold increase in DNMT3a levels and a significant decrease in MBD1 and MBD2 levels to ~30 % of control values. In white muscle, DNMT3a and DNMT3b increased threefold and MBD1 levels increased by 50 % in response to 5 h anoxia. Total DNMT activity rose by 0.6-2.0-fold in liver and white muscle and likewise global 5mC levels significantly increased in liver and white muscle under 5 and 20 h anoxia. The results demonstrate an overall increase in DNA methylation, DNMT protein expression and enzymatic activity in response to 5 and 20 h anoxia in liver and white muscle indicating a potential downregulation of gene expression via this epigenetic mechanism during oxygen deprivation.

Hibernation impacts lysine methylation dynamics in the 13‐lined ground squirrel, Ictidomys tridecemlineatus

“…Since the actions of KMTs on numerous proteins are known to regulate a plethora of cellular mechanisms (Biggar & Li, ), it is not likely that the role of protein methylation in regulating hypometabolism is exclusive to mammalian hibernation. Indeed, studies by our lab of lower vertebrate models of hypometabolism have recently shown that differential lysine methylation of both histone and nonhistone proteins as well as altered KMT activities and protein levels were components of anoxia tolerance by freshwater turtles ( Trachemys scriptaelegans ) and freezing survival by wood frogs ( Rana sylvatica ; Hawkins & Storey, ; Wijenayake & Storey, ). Interestingly, histone methylation modifications that are typically associated with active transcription were downregulated during freezing whereas those that act as transcriptional repressors were left intact.…”

“…Hawkins Wijenayake & Storey, 2016). Interestingly, histone methylation modifications that are typically associated with active transcription were downregulated during freezing whereas those that act as transcriptional repressors were left intact.…”

Epigenetic Underpinnings of Freeze Tolerance in the Goldenrod Gall Fly Eurosta Solidaginis and the Goldenrod Gall Moth Epiblema Scudderiana

“…Therefore, it follows that epigenetic mechanisms could underpin the reordering and suppression of transcription and other cellular processes during hypometabolic states. Indeed, this has been supported by a wide body of empirical evidence in numerous and diverse organisms (Padilla et al, 2002;Morin and Storey, 2006;Krivoruchko and Storey, 2013;Alvarado et al, 2014;Storey, 2015;Wijenayake and Storey, 2015;Zhao et al, 2015).…”

“…The vast majority (~60-70%) of DNA methylation occurs at CpG sites; these are regions of DNA where cytosine and guanine nucleotides are adjacent to each other separated by a phosphodiester bond. However certain regions containing an atypically high density of CpG sites, called CpG islands, are comparably unmethylated and become highly differentially methylated in different tissues in response to environmental stimuli (Bird, 2002;Wijenayake and Storey, 2015;Alvarado et al, 2014;Howlett and McGee, 2016). DNA methylation is necessary for normal patterns of gene expression and can result in permanent phenotypic modification as indicated by the critical role of this modification in tissue differentiation early in embryonic development and by the fact that aberrant patterns of DNA methylation are common biomarkers of cancer.…”

Regulation of DNA damage repair in response to freezing and anoxia in the wood frog, Rana sylvatica

“…many species insects, arthropods and others dig underground to place themselves below the frost line whereas others retreat underwater for the winter. The red-eared slider turtle (Trachemys scripta elegans) is an example of a reptile that finds a thermal buffered environment to survive the cold, as they overwinter under ice-locked lakes and ponds as their freeze avoidance strategy (Wijenayake and Storey, 2016). Other species that cannot avoid exposure to subzero environments instead produce their own antifreeze, producing high levels of cryoprotectants (such as sorbitol, glycerol, ribitol, mannitol, glucose, trehalose, etc.…”