Dynamic regulation of histone H3 lysine (K) acetylation and deacetylation during prolonged oxygen deprivation in a champion anaerobe

Reversible Histone Modifications Contribute to the Frozen and Thawed Recovery States of Wood Frog Brains

Epigenetic regulation, notably histone post-translational modification (PTM), has emerged as a major transcriptional control of gene expression during cellular stress adaptation. In the present study, we use an acid extraction method to isolate total histone protein and investigate dynamic changes in 23 well-characterized histone methylations/acetylations in the brains of wood frogs subject to 24-h freezing and subsequent 8-h thawed recovery conditions. Our results identify four histone PTMs (H2BK5ac, H3K14ac, H3K4me3, H3K9me2) and three histone proteins (H1.0, H2B, H4) that were significantly (p < 0.05) responsive to freeze-thaw in freeze-tolerant R. sylvatica brains. Two other permissive modifications (H3R8me2a, H3K9ac) also trended downwards following freezing stress. Together, these data are strongly supportive of the proposed global transcriptional states of hypometabolic freeze tolerance and rebounded thawed recovery. Our findings shed light on the intricate interplay between epigenetic regulation, gene transcription and energy metabolism in wood frogs' adaptive response to freezing stress.

Histone H3 and H4 Modifications Point to Transcriptional Suppression as a Component of Winter Freeze Tolerance in the Gall Fly Eurosta solidaginis

The goldenrod gall fly (Eurosta solidaginis) is a well-studied model of insect freeze tolerance. In situations of prolonged winter subzero temperatures, larvae of E. solidaginis accept ice penetration throughout extracellular spaces while protecting the intracellular environment by producing extreme amounts of glycerol and sorbitol as cryoprotectants. Hypometabolism (diapause) is implemented, and energy use is reprioritized to essential pathways. Gene transcription is one energy-expensive process likely suppressed over the winter, in part, due to epigenetic controls. The present study profiled the prevalence of 24 histone H3/H4 modifications of E. solidaginis larvae after 3-week acclimations to decreasing environmental temperatures (5 °C, -5 °C and -15 °C). Using immunoblotting, the data show freeze-mediated reductions (p < 0.05) in seven permissive histone modifications (H3K27me1, H4K20me1, H3K9ac, H3K14ac, H3K27ac, H4K8ac, H3R26me2a). Along with the maintenance of various repressive marks, the data are indicative of a suppressed transcriptional state at subzero temperatures. Elevated nuclear levels of histone H4, but not histone H3, were also observed in response to both cold and freeze acclimation. Together, the present study provides evidence for epigenetic-mediated transcriptional suppression in support of the winter diapause state and freeze tolerance of E. solidaginis.

Epigenetic underpinnings of freeze avoidance in the goldenrod gall moth, Epiblema scudderiana

The goldenrod gall moth (Epiblema scudderiana) is a cold hardy insect that survives subzero temperatures during the winter by supercooling bodily fluids to approximately -40 °C, allowing the insect to remain unfrozen despite the freezing temperatures. This is characterized by a drastic increase of cryoprotectant glycerol along with widespread downregulation of non-essential genes and processes to conserve cellular energy. This study examined the role of epigenetic enzymes in regulating this freeze-avoidant process across a range of freezing temperatures experienced in nature. Cold and subzero temperature exposure in E. scudderiana resulted in upregulation of select DNA methyltransferase (DNMT) enzymes with concurrent decreases in DNMT activity and no change in activity of the Ten-Eleven Translocation (TET) demethylation enzyme activities. Levels of histone acetyltransferase (HAT) and histone deacetylase (HDAC) activity decreased during cold exposures. The increase in DNMT expression and concurrent decrease in HAT activity suggests a role for DNA methylation to assist with transcriptional suppression. These findings propose that epigenetic regulation of genes and histones underpin the winter survival strategies of this insect.

Oxidative Damage? Not a Problem! The Characterization of Humanin-like Mitochondrial Peptide in Anoxia Tolerant Freshwater Turtles

Mitochondria was long thought to be an "end function" organelle that regulated the metabolic flux and apoptosis in the cell. However, with the discovery of the mitochondrial peptide (MDP) humanin (HN/MTRNR2), the cytoprotective and pro-survival applications of MDPs have taken the forefront of therapeutic and diagnostic research. However, the regulation of humanin-like MDPs in natural model systems that can tolerate lethal environmental and cytotoxic insults remains to be investigated. Red-eared sliders are champion anaerobes that can withstand three continuous months of anoxia followed by rapid bouts of oxygen reperfusion without incurring cellular damage. Freshwater turtles employ extensive physiological and biochemical strategies to combat anoxia, with metabolic rate depression and a global enhancement of antioxidant and cytoprotective pathways being the two most important contributors. The main aim of this study was to uncover and characterize the humanin-homologue in freshwater turtles as well as investigate the differential regulation of humanin in response to short and long-term oxygen deprivation. In this study we have used de novo and homology-based protein modelling to elucidate the putative structure of humanin in red-eared sliders as well as an ELISA and western immunoblotting to confirm the protein abundance in the turtle brain and six peripheral tissues during control, 5 h, and 20 h anoxia (n = 4/group). We found that a humanin-homologue (TSE-humanin) is present in red-eared sliders and it may play a cytoprotective role against oxidative damage.