Proteomics of cryoprotective dehydration in Megaphorura arctica Tullberg 1876 (Onychiuridae: Collembola)

The springtail Megaphorura arctica survives extremely high osmolality of body fluids during drought

The springtail Megaphorura arctica Tullberg 1876 is widespread in the arctic and subarctic regions where it can be abundant along beaches. This species survives winters using cryoprotective dehydration as a cold tolerance strategy during which it becomes drastically dehydrated. Several studies have investigated the physiological responses associated with water loss of M. arctica under exposure to freezing temperatures, but little is known of the dynamics of body water and hemolymph osmolality when subjected to gradually increasing drought stress at temperatures above the freezing point. Therefore, an experiment was conducted in which M. arctica was subjected to relative humidities (RH) decreasing from fully saturated conditions to ca. 89%RH over a period of 30 days. During the experiment water content of springtails decreased from about 3 to ca. 0.5 mg mg^-1 dry weight. Alongside with water loss, trehalose concentrations increased from nearly nothing to 0.12 mg mg^-1 dry weight, which contributed to an increase in hemolymph osmolality from ca. 250 mOsm to at least 7 Osm. All springtails survived water loss down to 0.7 mg mg^-1 dry weight and hemolymph osmolality of ca. 4 Osm, and about 60% of the springtails survived with only 0.5 mg water mg^-1 dry weight and osmolality of ca. 7 Osm. At this level of dehydration, Differential Scanning Calorimetry analysis showed that most, but not all, osmotically active water was lost. It is discussed that the extensive dehydration must be associated with high concentrations of salts potentially causing denaturation and precipitation of cellular proteins. M. arctica is remarkably tolerant of dehydration, but because it does not endure loss of the osmotically inactive water it cannot be categorized as a truly anhydrobiotic species.

The physiological role of fat body and muscle tissues in response to cold stress in the tropical cockroach Gromphadorhina coquereliana

Protective mechanisms against cold stress are well studied in terrestrial and polar insects; however, little is known about these mechanisms in tropical insects. In our study, we tested if a tropical cockroach Gromphadorhina coquereliana, possesses any protective mechanisms against cold stress. Based on the results of earlier studies, we examined how short-term (3 h) cold (4°C) influences biochemical parameters, mitochondrial respiration activity, and the level of HSPs and aquaporins expression in the fat body and leg muscles of G. coquereliana. Following cold exposure, we found that the level of carbohydrates, lipids and proteins did not change significantly. Nevertheless, we observed significant changes in mitochondrial respiration activity. The oxygen consumption of resting (state 4) and phosphorylating (state 3) mitochondria was altered following cold exposure. The increase in respiratory rate in state 4 respiration was observed in both tissues. In state 3, oxygen consumption by mitochondria in fat body was significantly lower compared to control insects, whereas there were no changes observed for mitochondria in muscle tissue. Moreover, there were cold-induced changes in UCP protein activity, but the changes in activity differed in fat body and in muscles. Additionally, we detected changes in the level of HSP70 and aquaporins expression. Insects treated with cold had significantly higher levels of HSP70 in fat body and muscles. On the other hand, there were lower levels of aquaporins in both tissues following exposure to cold. These results suggest that fat body play an important role in protecting tropical insects from cold stress.

Molecular snapshot of an intracellular freezing event in an Antarctic nematode

The Antarctic nematode, Panagrolaimus sp. DAW1 (formerly called Panagrolaimus davidi), is the best documented example of an organism able to survive intracellular ice formation in all of its compartments. Not only is it able to survive such extreme physiological disruption, but it is able to produce progeny once thawed from such a state. In addition, under slower rates, or less extreme degrees, of cooling, its body remains unfrozen and the vapour pressure difference between the supercooled body fluids and the surrounding ice leads to a process termed cryoprotective dehydration. In contrast to a fairly large body of work in building up our molecular understanding of cryoprotective dehydration, no comparable work has been undertaken on intracellular freezing. This paper describes an experiment subjecting cultures of Panagrolaimus sp. DAW1 to a range of temperatures including a rapid descent to -10 °C, in a medium just prior to, and after, freezing. Through deep sequencing of RNA libraries we have gained a snapshot of which genes are highly abundant when P. sp. DAW1 is undergoing an intracellular freezing event. The onset of freezing correlated with a high production of genes involved in cuticle formation and subsequently, after 24 h in a frozen state, protease production. In addition to the mapping of RNA sequencing, we have focused on a select set of genes arising both from the expression profiles, as well as implicated from other cold tolerance studies, to undertake qPCR. Among the most abundantly represented transcripts in the RNA mapping is the zinc-metalloenzyme, neprilysin, which also shows a particularly strong upregulated signal through qPCR once the nematodes have frozen.

Molecular analysis of the cold tolerant Antarctic nematode, Panagrolaimus davidi

Isolated and established in culture from the Antarctic in 1988, the nematode Panagrolaimus davidi has proven to be an ideal model for the study of adaptation to the cold. Not only is it the best-documented example of an organism surviving intracellular freezing but it is also able to undergo cryoprotective dehydration. As part of an ongoing effort to develop a molecular understanding of this remarkable organism, we have assembled both a transcriptome and a set of genomic scaffolds. We provide an overview of the transcriptome and a survey of genes involved in temperature stress. We also explore, in silico, the possibility that P. davidi will be susceptible to an environmental RNAi response, important for further functional studies.

Response to cold acclimation in diapause pupae of Hyles euphorbiae (Lepidoptera: Sphingidae): candidate biomarker identification using proteomics

The distribution range of Hyles euphorbiae covers distinct climates across the Palaearctic. Previous investigations showed a correlation between mitochondrial DNA identity of populations and climatic conditions related to winter; however, the lack of biomarkers hampers investigations to test whether geographically distinct populations do show specific molecular responses to low temperatures or whether they possess specific genetic identity at loci functionally related to cold response. The present study was designed to identify candidate protein biomarkers and biological processes that are associated with cold acclimation of overwintering H. euphorbiae diapause pupae. Specimens taken from a single central European population were gradually cooled from 20 °C to -2 °C over 36 days and 12 differentially abundant proteins were identified. In addition, DeepSuperSAGE sequencing technology was applied to study differentially regulated genes. There was incongruence between differentially abundant proteins and differentially expressed genes, but functional characteristics of regulated proteins and analyses of gene ontology term enrichment among differentially regulated genes pointed to activation of the same biological processes, e.g. oxidative stress response. As proteins represent biologically active molecules, candidate biomarkers derived from proteomics are considered well suited to explore intraspecific patterns of local adaptation to different climates.

Identification of differential expressed proteins and characterization their mRNA expression in thermally stressed Apostichopus japonicus

In this study, we present a comparative proteomic analysis of the global protein expression changes in sea cucumber after 7 days exposure at 25°C. Using two-dimensional electrophoresis followed by MALDI-TOF MS/MS, 27 protein spots with significant differences in abundance were identified and characterized. The identified proteins belonged primarily to the following four functional categories: cytoskeletal, material and energy metabolism, calcium homeostasis and extracellular matrix. The mRNA expression levels of 7 differentially expressed proteins were further assessed by qRT-PCR. The expression levels of 6 genes, including collagen, ATP synthase, major yolk protein, ferritin, nectin and protein disulfide isomerase showed significant differences under thermal stress, and among them, only two genes-ATP synthase and major yolk protein-showed consistent levels of protein and mRNA expression. Our results offer insight into the complex changes in protein turnover during higher temperature exposure in sea cucumber.

Global and comparative proteomic profiling of overwintering and developing mountain pine beetle, Dendroctonus ponderosae (Coleoptera: Curculionidae), larvae

BACKGROUND

Mountain pine beetles, Dendroctonus ponderosae Hopkins (Coleoptera: Curculionidae), are native to western North America, but have recently begun to expand their range across the Canadian Rocky Mountains. The requirement for larvae to withstand extremely cold winter temperatures and potentially toxic host secondary metabolites in the midst of their ongoing development makes this a critical period of their lives.

RESULTS

We have uncovered global protein profiles for overwintering mountain pine beetle larvae. We have also quantitatively compared the proteomes for overwintering larvae sampled during autumn cooling and spring warming using iTRAQ methods. We identified 1507 unique proteins across all samples. In total, 33 proteins exhibited differential expression (FDR < 0.05) when compared between larvae before and after a cold snap in the autumn; and 473 proteins exhibited differential expression in the spring when measured before and after a steady incline in mean daily temperature. Eighteen proteins showed significant changes in both autumn and spring samples.

CONCLUSIONS

These first proteomic data for mountain pine beetle larvae show evidence of the involvement of trehalose, 2-deoxyglucose, and antioxidant enzymes in overwintering physiology; confirm and expand upon previous work implicating glycerol in cold tolerance in this insect; and provide new, detailed information on developmental processes in beetles. These results and associated data will be an invaluable resource for future targeted research on cold tolerance mechanisms in the mountain pine beetle and developmental biology in coleopterans.

Insect cold hardiness: metabolic, gene, and protein adaptation1This review is part of a virtual symposium on recent advances in understanding a variety of complex regulatory processes in insect physiology and endocrinology, including development, metabolism, cold hardiness, food intake and digestion, and diuresis, through the use of omics technologies in the postgenomic era

Winter survival for thousands of species of insects relies on adaptive strategies for cold hardiness. Two basic mechanisms are widely used (freeze avoidance by deep supercooling and freeze tolerance where insects endure ice formation in extracellular fluid spaces), whereas additional strategies (cryoprotective dehydration, vitrification) are also used by some polar species in extreme environments. This review assesses recent research on the biochemical adaptations that support insect cold hardiness. We examine new information about the regulation of cryoprotectant biosynthesis, mechanisms of metabolic rate depression, role of aquaporins in water and glycerol movement, and cell preservation strategies (chaperones, antioxidant defenses and metal binding proteins, mitochondrial suppression) for survival over the winter. We also review the new information coming from the use of genomic and proteomic screening methods that are greatly widening the scope for discovery of genes and proteins that support winter survival.