Suspended animation,diapause and quiescence

Developing organisms require nutrients to support cell division vital for growth and development. An adaptation to stress, used by many organisms, is to reversibly enter an arrested state by reducing energy-requiring processes, such as development and cell division. This “wait it out” approach to survive stress until the environment is conductive for growth and development is used by many metazoans. Much is known about the molecular regulation of cell division, metazoan development and responses to environmental stress. However, how these biological processes intersect is less understood. Here, we review studies conducted in Caenorhabditis elegans that investigate how stresses such as oxygen deprivation (hypoxia and anoxia), exogenous chemicals or starvation affect cellular processes in the embryo, larvae or adult germline. Using C. elegans to identify how stress signals biological arrest can help in our understanding of evolutionary pressures as well as human health-related issues.     

Evidence for shallow‐water ‘Upper Kellwasser’ anoxia in the Frasnian–Famennian reefs of Alberta,Canada

The Frasnian–Famennian extinction witnessed the global devastation of both level‐bottom and reef communities in low latitudes. Marine extinctions in offshore level‐bottom communities are associated with two widespread, transgressive, anoxic ‘Kellwasser Events’ that support an anoxia–extinction link. Typical Kellwasser facies of bituminous limestones and shales are not obviously recorded in shallow‐water settings, and thus, it is unclear whether anoxia played a role in reef losses. We evaluate geochemical, petrographic and facies evidence for oxygen restriction from an extremely shallow‐water carbonate platform in Alberta. Sequence stratigraphy places the Frasnian–Famennian boundary at a sequence boundary that tops a laminated mudstone and interrupts carbonate platform deposition. Two transgressive pulses have been identified, one of which is associated with the second, major transgression of T‐R cycle IId of the Devonian eustatic sea‐level curve. Geochemical proxies indicate that these transgressions were accompanied by influx of dysoxic or anoxic waters. Organic carbon and U enrichment in the Frasnian, particularly just below the Frasnian–Famennian boundary, points to episodic dysoxic conditions that probably persisted into the basal Famennian and were coincidental with the global Upper Kellwasser Event. This study provides the first evidence for the smoking gun of an anoxia‐driven extinction in very shallow waters, implicating this potent killer in the demise of the Devonian reefs.     

Palaeoenvironmental changes across the Permian/Triassic boundary at Shangsi (N. Sichuan,China)

The section at Shangsi in Sichuan contains one of the most detailed and best records of events during the Permian/Triassic (P/T) mass extinction. Continuous deep water deposition is only punctuated by a minor shallowing in the late Changxingian. The micritic mudstones and wackestones of the Changxingian Dalong Formation contain abundant ammonoids and radiolaria and diverse and common benthic taxa (mostly bivalves and brachiopods) in a thoroughly bioturbated sediment. The presence of a well developed tiered burrow profile is just one line of evidence for a fully oxygenated water column in the late Permian. The faunal crisis occurs in the top few decimetres of the Dalong Formation and severely affected all groups (benthos, nekton and plankton). The extinction coincides precisely with the development of anaerobic and dysaerobic facies. The basal Triassic sediments of the Feixanguan Formation are thinnly‐bedded or laminated silicic marls and contain pyrite and several levels of elevated organic carbon concentrations. The fauna is restricted to rare ammonoids and a few bedding planes covered in Claraia. The presence of abundant coccoid cyanobacteria in these sediments may indicate an unusually simple trophic web in the early Triassic seas as these picoautotrophs are normally grazed by zooplankton, they are rarely directly incorporated into seafloor sediment. The recent discovery of black shales in P/T pelagic sediments of Japan indicates that the anoxic event also affected deep ocean waters and further strengthens the link between extinction and anoxia.     

Penehyclidine hydrochloride protects against anoxia/reoxygenation injury in cardiomyocytes through ATP‐sensitive potassium channels,and the Akt/GSK‐3β and Akt/mTOR signaling pathways

Penehyclidine hydrochloride (PHC) can protect against myocardial ischemia/reperfusion (I/R) injury. However, the possible mechanisms of PHC in anoxia/reoxygenation (A/R)‐induced injury in H9c2 cells remain unclear. In the present study, H9c2 cells were pretreated with PI3K/Akt inhibitor LY294002, ATP‐sensitive K⁺ (KATP) channel blocker 5‐hydroxydecanoate (5‐HD), PHC, or KATP channel opener diazoxide (DZ) before subjecting to A/R injury. Cell viability and cell apoptosis were determined by cell counting kit‐8 assay and annexin V/PI assay, respectively. Myocardial injury was evaluated by measuring creatine kinase (CK) and lactate dehydrogenase (LDH) activities. Intracellular Ca²⁺ levels, reactive oxygen species (ROS) generation, mitochondrial membrane potential (ΔΨ_m), and mitochondrial permeability transition pore (mPTP) were measured. The levels of cytoplasmic/mitochondrial cytochrome c (Cyt‐C), Bax, Bcl‐2, cleaved caspase‐3, KATP channel subunits (Kir6.2 and SUR2A), and the members of the Akt/GSK‐3β and Akt/mTOR signaling pathways were determined by western blotting. We found that PHC preconditioning alleviated A/R‐induced cell injury by increasing cell viability, reducing CK and LDH activities, and inhibiting cell apoptosis. In addition, PHC preconditioning ameliorated intracellular Ca²⁺ overload and ROS production, accompanied by inhibition of both mPTP opening and Cyt‐C release into cytoplasm, and maintenance of ΔΨ_m. Moreover, PHC preconditioning activated mitochondrial KATP channels, and modulated the Akt/GSK‐3β and Akt/mTOR signaling pathways. Similar effects were observed upon treatment with DZ. Pretreatment with LY294002 or 5‐HD blocked the beneficial effects of PHC. These results suggest that the protective effects of PHC preconditioning on A/R injury may be related to mitochondrial KATP channels, as well as the Akt/GSK‐3β and Akt/mTOR signaling pathways.     

Anoxia,acidosis, and intergenic interactions selectively regulate methionine sulfoxide reductase transcriptions in mouse embryonic stem cells

Methionine sulfoxide reductases (Msr) belong to a gene family that contains one MsrA and three MsrBs (MsrB1, MsrB2, and MsrB3). We have identified all four of the genes that are expressed in mouse embryonic stem cell cultures. The vital cellular functions of the Msr family of genes are to protect cells from oxidative damage by enzymatically reducing the oxidized sulfide groups of methionine residues in proteins from the sulfoxide form (? SO) back to sulfide thus restoring normal protein functions as well as reducing intracellular reactive oxygen species (ROS). We have performed studies on the Msr family genes to examine the regulation of gene expression. Our studies using real‐time RT‐PCR and Western blotting have shown that expression levels of the four Msr family genes are under differential regulation by anoxia/reoxygenation treatment, acidic culture conditions and interactions between MsrA and MsrB. Results from these in vitro experiments suggest that although these genes function as a whole in oxidative stress protection, each one of the Msr genes could be responsive to environmental stimulants differently at the tissue level. J. Cell. Biochem. 112: 98–106, 2011. © 2010 Wiley‐Liss, Inc.     

Overgrowth on ammonite conchs: environmental implications for the Lower Toarcian Posidonia Shale

Ammonites of the south–west German Posidonia Shale (Early Toarcian) are occasionally overgrown by bivalves, brachiopods or serpulids. Attachment to both sides of the conchs in some specimens suggests attachment during the ammonite's lifetime, with a pseudoplanktic mode of life for the epizoans. However, dense overgrowth restricted to the upper surface of some ammonite shells indicates post–mortem colonization. Our study shows that apart from oxygen supply as a main factor controlling benthic colonization, substrate consistency also played an important part. Unfavourable living conditions prevailed during deposition of the organic–rich sediments, excluding macrofauna in the benthic environment. However, less than 0.1 per cent of the ammonite conchs found during the excavation show overgrowth, indicating that pseudoplanktonism was an infrequently adopted strategy for inhabiting surface waters.     

Evidence for anaerobic metabolism in the larval tiger beetle, Phaeoxantha klugii (Col. Cicindelidae) from a Central Amazonian floodplain (Brazil)

Abstract. The tiger beetle, Phaeoxantha klugii Chaudoir, survives the annual inundation period in Central Amazonian floodplains as a third‐instar larvae submerged in the soil at approximately 29 °C for up to 3.5 months. Previous studies showed an exceptional anoxia resistance in these larvae and this study investigates whether they perform anaerobiosis. Larvae collected in the field were exposed to a pure nitrogen atmosphere for 0–9 days in the laboratory. The content of lactate, alanine, free sugars and glycogen is analysed in surviving larvae. Lactate and alanine contents rise during anoxia from around 1.5 and 7 to 6–14 and 15–22 µmol g^?1 fresh mass, respectively, providing evidence for anaerobic metabolism. Both compounds show a steep increase during the first 12 h and a tendency to rise further with increasing duration of anoxic conditions, indicating a significant metabolic depression within the first day. Content of free sugars and glycogen varies greatly between individuals and ranges from 0.08–2.5 and 0.05–2.9 mg g^?1 fresh mass, respectively. Whether glycogen is used as metabolic substrate for anaerobiosis could not be verified. The findings for free sugars indicate that larvae apparently maintain the ability to regulate the level of glucose and/or trehalose even after 9 days of anoxia.     

Oxygen concentrations inside the traps of the carnivorous plants Utricularia and Genlisea (Lentibulariaceae)

BACKGROUND AND AIMS: Species of Utricularia and Genlisea (Lentibulariaceae) are carnivorous, capturing small prey in traps which are physiologically very active, with abundant quadrifid and bifid glands. Traps of Utricularia have walls composed of two cell layers, and are filled with water. Diverse communities of commensal microorganisms often live inside the traps. Genlisea forms long, hollow subterranean traps of foliar origin, growing in anoxic wet substrate. Knowledge of the O(2) concentrations inside Utricularia and Genlisea traps is vital for understanding their physiological functioning and conditions for the life of commensals. To test the hypothesis that prey are killed by anoxia inside the traps, and to measure respiration of traps, [O(2)] was measured in the fluid in mature traps of these species. METHODS: Oxygen concentration and electrical redox potential were measured using a small Clark-type oxygen sensor and a miniature platinum electrode, respectively, in the fluid of excised and intact traps of six aquatic Utricularia species and in Genlisea hispidula traps. KEY RESULTS: Steady-state [O(2)] in the traps of both genera always approached zero (median 0.0-4.7 microm). The [O(2)] decreased after electrodes were inserted into Utricularia traps at a rate which ranged from 0.09 to 1.23 mm h(-1) and was lower in traps of irradiated and intact shoots with higher [O(2)] in shoot tissues. Redox potential ranged from -24 to -105 mV in the traps, confirming the very small or zero [O(2)]. CONCLUSIONS: Very small or zero [O(2)], effectively anoxia, is demonstrated in Utricularia and Genlisea traps. This is probably below the critical [O(2)] for prey survival, and causes captured prey to die of suffocation. Internal trap glands and trap commensals are considered to be adapted to facultative anoxia interrupted by limited periods of higher [O(2)] after firings.