Living without Oxygen: Anoxia-Responsive Gene Expression and Regulation

Abstract

Many species of marine mollusks demonstrate exceptional capacities for long term survival without oxygen. Analysis of gene expression under anoxic conditions, including the subsequent translational responses, allows examination of the functional mechanisms that support and regulate natural anaerobiosis and permit noninjurious transitions between aerobic and anoxic states. Identification of stress-specific gene expression can provide important insights into the metabolic adaptations that are needed for anoxia tolerance, with potential applications to anoxia-intolerant systems. Various methods are available to do this, including high throughput microarray screening and construction and screening of cDNA libraries. Anoxia-responsive genes have been identified in mollusks; some have known functions in other organisms but were not previously linked with anoxia survival. In other cases, completely novel anoxia-responsive genes have been discovered, some that show known motifs or domains that hint at function. Selected genes are expressed at different times over an anoxia-recovery time course with their transcription and translation being actively regulated to ensure protein expression at the optimal time. An examination of transcript status over the course of anoxia exposure and subsequent aerobic recovery identifies genes, and the proteins that they encode, that enhance cell survival under oxygen-limited conditions. Analysis of data generated from non-mainstream model systems allows for insight into the response by cells to anoxia stress.

Evidence for cell cycle suppression and microRNA regulation of cyclin D1 during anoxia exposure in turtles

“…The supernatant was removed, and tubes were allowed to dry for 10-15 min and then resuspended in 50 μL diethyl pyrocarbonate (DEPC)-treated H 2 O. RNA quality was assessed by the 260/280 nm ratio as well as gel electrophoresis on a 1% agarose gel stained with 2x Sybr Green I (Cat# S7563; Invitrogen) to check for integrity of the 18S and 28S rRNA bands. All RNA samples were diluted to 1 μg/μL using DEPC-treated ddH 2 and stored at -20°C. MicroRNA specific reverse transcription was performed as previously described in reference 40.…”

“…1 Oxygen deprivation has severe consequences for cellular energy production, and for intolerant species, even small fluctuation in oxygen availability can be lethal. 2 Turtles are able to achieve this impressive facultative anaerobiosis using mechanisms including: (1) strong metabolic rate suppression, (2) a high capacity for glycolytic energy production and (3) effective methods for dealing with end products (acid buffering, lactate storage in shell). 3,4 Molecular mechanisms of metabolic rate depression include a global suppression of energy-utilizing processes and a reprioritization of ATP use to support cell functions that are vital for the red-eared slider turtle (Trachemys scripta elegans) has a well-developed natural tolerance for oxygen deprivation that derives from biochemical adaptations, including anoxia-induced suppression of metabolic rate.…”

“…3 Reversible phosphorylation of proteins has proven to be one such regulatory mechanism that exerts wide-ranging control over metabolism under anoxia. [1][2][3] Interestingly, the characteristics of microRNA regulation toward mRNA transcripts also fulfills these requirements and may, therefore, be key to both translational suppression and transcript storage in the anoxic state.…”

Effects of temperature and cadmium exposure on the mitochondria of oysters (Crassostrea virginica) exposed to hypoxia and subsequent reoxygenation

“…In oyster, several isoforms of uncoupling proteins are expressed but do not appear to contribute to physiological proton leak (Cherkasov et al, 2007a;Sokolova and Sokolov, 2005) indicating that other molecular mechanisms (such as activities of substrate transporters or cation pumps) may be involved in regulating the mitochondrial proton conductance. Regardless of their exact molecular mechanisms, elevated proton conductance and enhanced capacity of phosphorylation and substrate oxidation subsystems can preserve aerobic capacity and protect mitochondrial integrity of oysters during periodic hypoxia/reoxygenation in the coastal and estuarine habitats, especially if coupled with the hypoxia-induced upregulation of antioxidants such as shown in other intertidal mollusks (English and Storey, 2003;Hermes-Lima et al, 1998;Larade and Storey, 2009;Pannunzio and Storey, 1998). …”

The effects of hypoxia on active ionic transport processes in the gill epithelium of hyperregulating crab, Carcinus maneas

“…Invertebrate survival during Č. Lucu, A. Ziegler Comparative Biochemistry and Physiology, Part A 211 (2017) 61-68 hypoxia is made possible primarily by ATP conservation (Larade and Storey, 2009;Gorr et al, 2006). During this state the most energetically expensive cellular functions, such as the Na + /K + pump, are drastically suppressed,thereby reducing overall ATP consumption to match the concomitant decline in ATP supply and achieving a balanced homeostasis (Boutilier and St. Pierre, 2000;Hochachka and Somero, 2002;Gorr et al, 2006).…”