Dynamic regulation of histone arginine methylation in anoxic freshwater turtles.

Reversible depression of transcriptional and translational processes are commonly exhibited during animal hypometabolic responses, including the anoxia tolerance of freshwater red-eared slider (Trachemys scripta elegans) turtles. Recent evidence has implicated histone lysine methylation and acetylation in transcriptional regulation of red-eared sliders under anoxic conditions, however investigation into other epigenetic mechanisms, like arginine methylation, are currently lacking. Here, we examine the relative expression of the protein arginine methyltransferase (PRMT) family, known methyl-arginine “erasers” and methyl-arginine binding TUDOR proteins in T.s. elegans liver across 5-hour and 20-hour anoxic conditions. We also use histone isolates to profile the relative abundance of core histone proteins and putative histone methyl-arginine modifications. Numerous proteins involved in arginine methylation were responsive (p < 0.05) to anoxia. Elevated steady-state protein levels were observed for the monomethyltransferase PRMT7 and deiminase PADI4 across both anoxic conditions. On the contrary, symmetric dimethyl-arginine (SDMA)-producing PRMT5 and SDMA-binding SND1 were lowered from 5-hour and 20-hour anoxic exposures. Suggested roles for dynamic PRMT8, PRMT9 and JMJD1A expression under specific anoxic conditions are also discussed. At the histone level, linker histone H1.0 was raised 2.1 ± 0.3-fold after 5 h while the transcriptionally permissive PTM H3R8me2a was reduced to 63 ± 11% of controls after 20 h, both suggestive of gene silencing during anoxia. This work adds an additional layer to the epigenetic framework and indicates arginine methylation in hypometabolic anoxia tolerance of freshwater turtles.