Challenges during diapause and anhydrobiosis: Mitochondrial bioenergetics and desiccation tolerance (original) (raw)
Related papers
Physiological and Biochemical Zoology, 2013
Diapause embryos were collected from ovigerous females of Artemia franciscana at the Great Salt Lake, Utah, and were synchronized to within 4 h of release. Respiration rate for these freshly released embryos across a subsequent 26-d time course showed a rapid decrease during the first several days followed thereafter by a much slower decline. The overall metabolic depression was estimated to be greater than 99%. However, proton conductance of mitochondria isolated from diapause and postdiapause embryos was identical. Because proton leak is apparently not downregulated during diapause, mitochondrial membrane potential is likely compromised because of the very low metabolic rate observed for diapause embryos. Given that trehalose is the primary fuel used by these embryos, we measured metabolic intermediates along the catabolic pathway from trehalose to acetyl-CoA for both diapause and postdiapause (active) embryos in order to identify sites of metabolic inhibition. Comparison of product-to-substrate ratios for sequential enzymatic steps revealed inhibition during diapause at trehalase, hexokinase, pyruvate kinase, and pyruvate dehydrogenase. Measurements of ATP, ADP, and AMP allowed calculations of substantial decreases in ATP : ADP ratio and in adenylate energy charge during diapause. The phosphorylation of site 1 for pyruvate dehydrogenase (PDH) subunit E1a was higher in diapause embryos than in postdiapause embryos, which is consistent with PDH inhibition during diapause. Taken together, our findings indicate that restricted substrate availability to mitochondria for oxidative phosphorylation contributes to downregulating metabolic rate during diapause.
Metabolism and gene expression during diapause in athropods
2007
Arthropods may enter diapause to escape environmental insult. Diapause is an endogenously controlled dormant state defined by developmental arrest and species-specific physiological changes (e.g., metabolic depression and upregulation of compounds that protect cell structure and function). Although physiological changes have been documented for a number of species in diapause, biochemical and molecular regulation of diapause remains largely unexplained. Aerobic metabolism in diapause, Artemia franciscana, embryos is reduced up to 92 % compared with post-diapause embryos. Differences in isolated mitochondria are insufficient to account for respiratory depression because mitochondria in diapause embryos are structurally similar to mitochondria in post-diapause embryos. Respiratory control ratios and P:O flux ratios of mitochondria from diapause embryos are equal to or higher than those of mitochondria from postdiapause embryos. State 3 and state 4 respiration rates on pyruvate are equivalent in the two stages, and mitochondria isolated from diapause embryos show a moderate, 15-27 % reduction with succinate. Cytochrome c oxidase activity is 53 % lower in diapause embryos, but the minimal impact on mitochondrial respiration appears to be due to the 31 % excess of COX capacity in these embryos. Allonemobius socius embryos enter diapause 3-4 d post-oviposition as indicated by their morphology and DNA embryo-1. There is not an acute downregulation of metabolism during diapause in this species. Diapause embryos consume O 2 at the same rate as morphologically similar non-diapause embryos. Diapause and non-diapause embryos exhibit unusually high [AMP]/[ATP] and low [ATP]/[ADP] during early embryogenesis, suggesting that these embryos may be hypoxic early in development. However, superfusing 3 d embryos with O 2 enriched air only partially relieves the hypoxic state, which indicates the unusual energy status is an ontogenetic feature not fully explained by oxygen limitation. vi Subtractive hybridization and qPCR identified 6 genes predicted to regulate diapause entry in A. socius. Reptin, TFDp2, CYP450, AKR are significantly upregulated in pre-diapause embryos, and ACLY and Capthesin B-like protease are downregulated compared to non-diapause embryos. The need for genes upregulated in pre-diapause embryos appears to be transient as these genes are substantially downregulated 10 d after diapause entry. Taken together, these studies provide an integrative examination of mechanisms underlying diapause entry in arthropods.
Regulation of embryonic diapause inArtemia: Environmental and physiological signals
The journal of experimental zoology, 1987
Environmental cues terminating embryonic diapause and a potential regulatory mechanism involving depressed pH were investigated in the encysted embryos of the brine shrimp, Artemia Two species, Artemia franciscana and Artemia monica, were used for this comparative study. To determine if alteration of intracellular pH (pHJ can terminate diapause, the pHi of diapause cysts was manipulated by exposure to NH3 and COZ. Alkalinization did not result in activation of cysts from either species but acidification activated A. franciscana cysts. A. monica did not respond to acidification. The pHi of aerobic diapausing embryos was determined using 31P nuclear magnetic resonance spectroscopy. During diapause, embryos from both species had pHi's similar to those reported for activated (nondiapause) embryos, indicating that diapause is not imposed by depressed pHi, as is the case during suppression of metabolism under anaerobic conditions. Diapause embryos were exposed to varying conditions of temperature, salinity, and oxygen to determine what conditions are necessary to break diapause. A. franciscana cysts were activated by cold temperature or salinities above 2.0 M NaC1, while A. monica cysts only responded to cold temperature. The availability of oxygen did not influence either population's ability to terminate diapause. The results are discussed with respect to each population's environment and potential mechanisms of diapause regulation.
Marine Environmental Research, 2008
Spatial and temporal increases of hypoxia in estuaries are of major environmental concern. Since mitochondria consume most of the oxygen in the cell, we examined the potential role of mitochondrial gene and protein expression in adaptation to chronic hypoxia in the grass shrimp Palaemonetes pugio. Grass shrimp were exposed to DO levels slightly above and below the critical pO 2 , 1.8 mg/L, for P. pugio, and hypoxia-induced alterations in gene expression were screened using custom cDNA macroarrays. Mitochondrial gene expression was not affected by exposure to moderate hypoxia (2.5 mg/L DO). However, chronic exposure to severe hypoxia (1.5 mg/L DO) for 7 days resulted in an increase of transcription of genes present in the mitochondrial genome (including 16S rRNA and Ccox 1), together with up-regulation of genes
Molecular Anhydrobiology: Identifying Molecules Implicated in Invertebrate Anhydrobiosis
Integrative and Comparative Biology, 2005
SYNOPSIS. Studies in anhydrobiotic plants have defined many genes which are upregulated during desiccation, but comparable studies in invertebrates are at an early stage. To develop a better understanding of invertebrate anhydrobiosis, we have begun to characterise dehydration-inducible genes and their proteins in anhydrobiotic nematodes and bdelloid rotifers; this review emphasises recent findings with a hydrophilic nematode protein. Initial work with the fungivorous nematode Aphelenchus avenae led to the identification of two genes, both of which were markedly induced on slow drying (90-98% relative humidity, 24 hr) and also by osmotic stress, but not by heat or cold or oxidative stresses. The first of these genes encodes a novel protein we have named anhydrin; it is a small, basic polypeptide, with no counterparts in sequence databases, which is predicted to be natively unstructured and highly hydrophilic. The second is a member of the Group 3 LEA protein family; this and other families of LEA proteins are widely described in plants, where they are most commonly associated with the acquisition of desiccation tolerance in maturing seeds. Like anhydrin, the nematode LEA protein, Aav-LEA-1, is highly hydrophilic and a recombinant form has been shown to be unstructured in solution. In vitro functional studies suggest that Aav-LEA-1 is able to stabilise other proteins against desiccation-induced aggregation, which is in keeping with a role of LEA proteins in anhydrobiosis. In vivo, however, Aav-LEA-1 is apparently processed into smaller forms during desiccation. A processing activity was found in protein extracts of dehydrated, but not hydrated, nematodes; these shorter polypeptides are also active anti-aggregants and we hypothesise that processing LEA protein serves to increase the number of active molecules available to the dehydrating animal. Other LEA-like proteins are being identified in nematodes and it seems likely therefore that they will play a major role in the molecular anhydrobiology of invertebrates, as they are thought to do in plants.