Mitochondria-derived Small Non-coding RNAs in Extreme Anoxia Tolerance
The FASEB Journal
Mitochondria are critical sensors of oxygen and play a major role in the regulation of the cellular response to oxygen deprivation. Understanding mitochondrial function during transitions into and out of anoxia in species that can tolerate anoxia may lend new insights into the role that mitochondria play in cellular homeostasis in response to fluctuating levels of oxygen. The objective of this study was to examine the potential role of small RNAs in long-term vertebrate anoxia tolerance. Expression patterns of small RNAs were determined using RNAseq in the most anoxia tolerant vertebrate, embryos of the annual killifishAustrofundulus limnaeus. Anoxia tolerance varies during development in this species in a way that allows for the comparison of developmental stages with extreme anoxia tolerance to stages with a more typical vertebrate anoxia tolerance. Embryos of 4 different developmental stages were exposed to anoxia, followed by aerobic recovery, and small RNA expression was determined with Illumina RNAseq under aerobic conditions, anoxia, and during aerobic recovery. A large proportion of the differentially expressed small RNAs were found to be encoded in the mitochondrial genome. About 12% of the unique small RNAs identified were encoded within the mitochondrial genome, and around 20% of the highly differentially expressed RNAs in response to anoxia were mitochondrial in origin. Of the differentially expressed sequences mapping to the mitochondrial genome, small RNAs derived from mitochondrial tRNAs were particularly enriched, with sequences up-regulated during anoxia and aerobic recovery from anoxia. These small RNAs of interest localize to anoxia sensitive tissues, such as the brain and heart, providing further evidence for a potential role in supporting anoxia tolerance. These same small RNAs have been detected in cell cultures derived from A. limnaeus embryos, by RNAseq and in situ hybridization. Cell culture expression patterns corroborated whole-embryo sequence expression patterns. This work highlights a potential new class of small RNAs derived from the mitochondrial genome that may act to mediate and coordinate the physiological response to anoxia in this species. Further understanding the biology of these mitochondrially-derived small RNAs and their role in anoxia tolerance may provide novel insight into combating cellular damage induced by heart attack and stroke, two lethal consequences of heart disease in humans.
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Riggs, C. L., & Podrabsky, J. E. (2017). Mitochondria-derived Small Non-coding RNAs in Extreme Anoxia Tolerance. The FASEB Journal, 31(1 Supplement), 1080-2.