ArHsp22, a developmentally regulated small heat shock protein produced in diapause-destined Artemia embryos, is stress inducible in adults

Integrating ATAC-Seq and RNA-Seq Reveals the Signal Regulation Involved in the Artemia Embryonic Reactivation Process

Embryonic diapause is a common evolutionary adaptation observed across a wide range of organisms. Artemia is one of the classic animal models for diapause research. The current studies of Artemia diapause mainly focus on the induction and maintenance of the embryonic diapause, with little research on the molecular regulatory mechanism of Artemia embryonic reactivation. The first 5 h after embryonic diapause breaking has been proved to be most important for embryonic reactivation in Artemia. In this work, two high-throughput sequencing methods, ATAC-seq and RNA-seq, were integrated to study the signal regulation process in embryonic reactivation of Artemia at 5 h after diapause breaking. Through the GO and KEGG enrichment analysis of the high-throughput datasets, it was showed that after 5 h of diapause breaking, the metabolism and regulation of Artemia cyst were quite active. Several signal transduction pathways were identified in the embryonic reactivation process, such as G-protein-coupled receptor (GPCR) signaling pathway, cell surface receptor signaling pathway, hormone-mediated signaling pathway, Wnt, Notch, mTOR signaling pathways, etc. It indicates that embryonic reactivation is a complex process regulated by multiple signaling pathways. With the further protein structure analysis and RT-qPCR verification, 11 GPCR genes were identified, in which 5 genes function in the embryonic reactivation stage and the other 6 genes contribute to the diapause stage. The results of this work reveal the signal transduction pathways and GPCRs involved in the embryonic reactivation process of Artemia cysts. These findings offer significant clues for in-depth research on the signal regulatory mechanisms of the embryonic reactivation process and valuable insights into the mechanism of animal embryonic diapause.

ArHsp90 is important in stress tolerance and embryo development of the brine shrimp, Artemia franciscana

Females of the extremophile crustacean, Artemia franciscana, either release motile nauplii via the ovoviviparous pathway or encysted embryos (cysts) via the oviparous pathway. Cysts contain an abundant amount of the ATP-independent small heat shock protein that contributes to stress tolerance and embryo development, however, little is known of the role of ATP-dependent molecular chaperone, heat shock protein 90 (Hsp90) in the two processes. In this study, a hsp90 was cloned from A. franciscana. Characteristic domains of ArHsp90 were simulated from the deduced amino acid sequence, and 3D structures of ArHsp90 and Hsp90s of organisms from different groups were aligned. RNA interference was then employed to characterize ArHsp90 in A. franciscana nauplii and cysts. The partial knockdown of ArHsp90 slowed the development of nauplius-destined, but not cyst-destined embryos. ArHsp90 knockdown also reduced the survival and stress tolerance of nauplii newly released from A. franciscana females. Although the reduction of ArHsp90 had no effect on the development of diapause-destined embryos, the resulting cysts displayed reduced tolerance to desiccation and low temperature, two stresses normally encountered by A. franciscana in its natural environment. The results reveal that Hsp90 contributes to the development, growth, and stress tolerance of A. franciscana, an organism of practical importance as a feed source in aquaculture.

Prolonged ecological changes can affect morphometrics and gene expression profile? Focusing on Hsp-70 and NLHS-induced Hsp-70 of Artemia urmiana

BACKGROUND

In recent years, many aquatic ecosystems, including Urmia Lake, have undergone severe ecological tensions. This lake, the largest natural habitat of the brine shrimp Artemia urmiana, has progressively desiccated and its salinity has dramatically increased over the last three decades. In the face of the long period environmental stresses, understanding the adaptation and ecological plasticity mechanisms is the most interesting challenges in genetic and applied ecology. These mechanisms may probably be driven by inducing expression of some genes involved in adaptation such as Hsp-70 and also adjusting morphological parameters. But they are yet to be understood. Hence, the present work aimed to study the mechanisms, along with testing the hypothesis that non-lethal heat shocked nauplii originating from drought period can evoke Hsp-70 expression more than those from rainy period.

METHODS

This study measured and analyzed morphometrical characters of adult male and female Artemia urmiana over three decades. Then, the influence of three-decade ecological crisis on Hsp-70 and non-lethal heat shock (NLHS)-induced Hsp-70 expression levels of nauplii of Artemia urmiana habiting Urmia Lake using Real-time PCR technique, based on cyst collections in 1994 (rainy period) to 2020 (drought period), was evaluated.

RESULTS

The morphometrics results showed that the morphological characters were significantly shrunk in 2020 compared to 1994 (CI 95%, p < 0.05). Furthermore, our results depicted that, Hsp-70 expression level was significantly upregulated in response to the prolonged ecological crisis, (CI 95%, P < 0.0001), and also interestingly, the nauplii exposed to longe-term ecological crisis (belong to 2020) were able to increase Hsp-70 expression more than other ones in response to environmental stressors including heat.

CONCLUSIONS

The present results showed the involvement of Hsp-70 in the adaptation of Artemia urmiana to long term ecological alteration at the cost of shrinking morphometric parameters.

Effect of Different Culture Conditions on Gene Expression Associated With Cyst Production in Populations of Artemia franciscana

Artemia franciscana inhabits hypersaline environments in the Americas and has a well-adapted reproductive system that allows it to survive in these extreme conditions, represented by the production of diapause cysts (oviparous reproduction). This reproduction mode is controlled by numerous genes that are expressed in response to different environmental stressors, enabling this species to avoid population extinction. However, to date, the expression of these genes has not been sufficiently studied to clarify their levels in response to a combination of different environmental factors under controlled conditions. We analyzed the expression of eight genes related to oviparous reproduction (SGEG, Arp-CBP, artemin, BRCA1, p8, ArHsp21, ArHsp22, and p26) to determine their association with cyst production in two populations of A. franciscana with contrasting phenotypes, one with high (Barro Negro, BNE, Chile) and one with low (San Francisco Bay, SFB, United States) cyst production. Populations were cultured under controlled conditions of salinity (SAL, 35 and 75 ppt), photoperiod (PHO, 12L:12D and 24L:00D), iron concentration (IC, 0[Fe] and 5[Fe]), and microalgae diet (DIE; Dunaliella tertiolecta (DUN) and Tetraselmis suecica (TETRA)). Sixteen treatments were performed by combining the two conditions of each of the four factors. Data on nine reproductive parameters per female were recorded, including the percent of offspring encysted (%) (POE). The gene expression levels were analyzed by semiquantitative RT-PCR. The mean POE was significantly greater in BNE than in SFB (32.40 versus 12.74%, Mann-Whitney's test, p < 0.05). Significantly upregulated expression of seven genes in BNE (more than twofold, p < 0.05) was observed in 38.28% of the treatments (e.g., DUN-75ppt-12L:12D-5[Fe] and TETRA-35ppt-12L:12D-5[Fe]). In SFB, seven genes showed significant differential expression, but most were downregulated in 29.69% of the treatments (e.g., DUN-75ppt-12L:12D-0[Fe] and DUN-75ppt-24L:00D-0[Fe]). Multiple regression analyses indicated that in BNE, five genes (SGEG, artemin, Arp-CBP, p8, and BRCA1) and three environmental factors (DIE, SAL, and IC) were important predictor variables for the POE response variable given that all of them were included in the highest-ranking models. In SFB, only two genes (ArHsp21 and artemin) and one environmental factor (SAL) were important explanatory variables in the highest-ranking models. It was concluded that the BNE population presented a characteristic gene expression pattern that differed from that of the SFB population. This pattern might be related to the marked oviparous reproduction of the BNE population. This gene expression pattern could be useful for monitoring the reproductive mode leading to diapause in Artemia and to assist with intensive cyst production in pond systems.

Transcriptomic analysis elucidates the molecular processes associated with hydrogen peroxide-induced diapause termination in Artemia-encysted embryos

Treatment with hydrogen peroxide (H₂O₂) raises the hatching rate through the development and diapause termination of Artemia cysts. To comprehend the upstream genetic regulation of diapause termination activated by exterior H₂O₂ elements, an Illumina RNA-seq analysis was performed to recognize and assess comparative transcript amounts to explore the genetic regulation of H₂O₂ in starting the diapause termination of cysts in Artemia salina. We examined three groupings treated with no H₂O₂ (control), 180 μM H₂O₂ (low) and 1800 μM H₂O₂ (high). The results showed a total of 114,057 unigenes were identified, 41.22% of which were functionally annotated in at least one particular database. When compared to control group, 34 and 98 differentially expressed genes (DEGs) were upregulated in 180 μM and 1800 μM H₂O₂ treatments, respectively. On the other hand, 162 and 30 DEGs were downregulated in the 180 μM and 1800 μM H₂O₂ treatments, respectively. Cluster analysis of DEGs demonstrated significant patterns among these types of 3 groups. GO and KEGG enrichment analysis showed the DEGs involved in the regulation of blood coagulation (GO: 0030193; GO: 0050818), regulation of wound healing (GO:0061041), regulation of hemostasis (GO: 1900046), antigen processing and presentation (KO04612), the Hippo signaling pathway (KO04391), as well as the MAPK signaling pathway (KO04010). This research helped to define the diapause-related transcriptomes of Artemia cysts using RNA-seq technology, which might fill up a gap in the prevailing body of knowledge.

Structure, gene expression, and putative functions of crustacean heat shock proteins in innate immunity

Heat shock proteins (HSPs) are molecular chaperones with critical roles in the maintenance of cellular proteostasis. HSPs, which regulate protein folding and refolding, assembly, translocation, and degradation, are induced in response to physiological and environmental stressors. In recent years, HSPs have been recognized for their potential role in immunity; in particular, these proteins elicit a variety of immune responses to infection and modulate inflammation. This review focuses on delineating the structural and functional roles of crustacean HSPs in the innate immune response. Members of crustacean HSPs include high molecular weight HSPs (HSP90, HSP70, and HSP60) and small molecular weight HSPs (HSP21 and HSP10). The sequences and structures of these HSPs are highly conserved across various crustacean species, indicating strong evolutionary links among this group of organisms. The expression of HSP-encoding genes across different crustacean species is significantly upregulated upon exposure to a wide range of pathogens, emphasizing the important role of HSPs in the immune response. Functional studies of crustacean HSPs, particularly HSP70s, have demonstrated their involvement in the activation of several immune pathways, including those mediating anti-bacterial resistance and combating viral infections, upon heat exposure. The immunomodulatory role of HSPs indicates their potential use as an immunostimulant to enhance shrimp health for control of disease in aquaculture.

Short-term cold stress and heat shock proteins in the crustacean Artemia franciscana

In their role as molecular chaperones, heat shock proteins (Hsps) mediate protein folding thereby mitigating cellular damage caused by physiological and environmental stress. Nauplii of the crustacean Artemia franciscana respond to heat shock by producing Hsps; however, the effects of cold shock on Hsp levels in A. franciscana have not been investigated previously. The effect of cold shock at 1 °C followed by recovery at 27 °C on the amounts of ArHsp90, Hsp70, ArHsp40, and ArHsp40-2 mRNA and their respective proteins in A. franciscana nauplii was examined by quantitative PCR (qPCR) and immunoprobing of western blots. The same Hsp mRNAs and proteins were also quantified during incubation of nauplii at their optimal growth temperature of 27 °C. qPCR analyses indicated that the abundance of ArHsp90, Hsp70, and ArHsp40 mRNA remained relatively constant during both cold shock and recovery and was not significantly different compared with levels at optimal temperature. Western blotting revealed that ArHsp90, ArHsp40, and ArHsp40-2 were generally below baseline, but at detectable levels during the 6 h of cold shock, and persisted in early recovery stages before declining. Hsp70 was the only protein that remained constant in quantity throughout cold shock and recovery. By contrast, all Hsps declined rapidly during 6 h when nauplii were incubated continuously at 27 °C optimal temperature. Generally, the amounts of ArHsp90, ArHsp40, and ArHsp40-2 were higher during cold shock/recovery than those during continuous incubation at 27 °C. Our data support the conclusion that low temperature preserves Hsp levels, making them available to assist in protein repair and recovery after cold shock.

Mechanisms of Desiccation Tolerance: Themes and Variations in Brine Shrimp, Roundworms, and Tardigrades

Water is critical for the survival of most cells and organisms. Remarkably, a small number of multicellular animals are able to survive nearly complete drying. The phenomenon of anhydrobiosis, or life without water, has been of interest to researchers for over 300 years. In this review we discuss advances in our understanding of protectants and mechanisms of desiccation tolerance that have emerged from research in three anhydrobiotic invertebrates: brine shrimp (Artemia), roundworms (nematodes), and tardigrades (water bears). Discovery of molecular protectants that allow each of these three animals to survive drying diversifies our understanding of desiccation tolerance, and convergent themes suggest mechanisms that may offer a general model for engineering desiccation tolerance in other contexts.

Characteristics, dynamics and mechanisms of actions of some major stress-induced biomacromolecules; addressing Artemia as an excellent biological model

Stress tolerance is one of the most prominent and interesting topics in biology since many macro- and micro-adaptations have evolved in resistant organisms that are worth studying. When it comes to confronting various environmental stressors, the extremophile Artemia is unrivaled in the animal kingdom. In the present review, the evolved molecular and cellular basis of stress tolerance in resistant biological systems are described, focusing on Artemia cyst as an excellent biological model. The main purpose of the review is to discuss how the structure and physicochemical characteristics of protective factors such as late embryogenesis abundant proteins (LEAPs), small heat shock proteins (sHSPs) and trehalose are related to their functions and by which mechanisms, they exert their functions. In addition, some metabolic depressors in Artemia encysted embryos are also mentioned, indirectly playing important roles in stress tolerance. Importantly, a great deal of attention is given to the LEAPs, exhibiting distinctive folding behaviors and mechanisms of actions. For instance, molecular shield function, chaperone-like activity, moonlighting property, sponging and snorkeling capabilities of the LEAPs are delineated here. Moreover, the molecular interplay between some of these factors is mentioned, leading to their synergistic effects. Interestingly, Artemia life cycle adapts to environmental conditions. Diapause is the defense mode of this life cycle, safeguarding Artemia encysted embryos against various environmental stressors. Communicated by Ramaswamy H. Sarma.

The synthesis of diapause-specific molecular chaperones in embryos of Artemia franciscana is determined by the quantity and location of heat shock factor 1 (Hsf1)

The crustacean, Artemia franciscana, displays a complex life history in which embryos either arrest development and undertake diapause as cysts or they develop into swimming nauplii. Diapause entry is preceded during embryogenesis by the synthesis of specific molecular chaperones, namely the small heat shock proteins p26, ArHsp21, and ArHsp22, and the ferritin homolog, artemin. Maximal synthesis of diapause-specific molecular chaperones is dependent on the transcription factor, heat shock factor 1 (Hsf1), found in similar amounts in cysts and nauplii newly released from females. This investigation was performed to determine why, if cysts and nauplii contain comparable amounts of Hsf1, only cyst-destined embryos synthesize diapause-specific molecular chaperones. Quantification by qPCR and immunoprobing of Western blots, respectively, demonstrated that hsf1 mRNA and Hsf1 peaked by day 2 post-fertilization in embryos that were developing into cysts and then declined. hsf1 mRNA and Hsf1 were present in nauplii-destined embryos on day 2 post-fertilization, but in much smaller amounts than in cyst-destined embryos, and they increased in quantity until release of nauplii from females. Immunofluorescent staining revealed that the amount of Hsf1 in nuclei was greatest on day 4 post-fertilization in cyst-destined embryos but could not be detected in nuclei of nauplius-destined embryos at this time. The differences in quantity and location of Hsf1 explain why embryos fated to become cysts and eventually enter diapause synthesize p26, ArHsp21, ArHsp22, and artemin, whereas nauplius-destined embryos do not produce these molecular chaperones.

Knockdown of the small heat-shock protein p26 by RNA interference modifies the diapause proteome of Artemia franciscana

Embryos of the crustacean Artemia franciscana may arrest as gastrulae, forming cysts that enter diapause, which is a state of reduced metabolism and enhanced stress tolerance. Diapausing cysts survive physiological stresses for years due, in part, to molecular chaperones. p26, a small heat-shock protein, is an abundant diapause-specific molecular chaperone in cysts, and it affects embryo development and stress tolerance. p26 is therefore thought to influence many proteins in cysts, and this study was undertaken to determine how the loss of p26 by RNA interference (RNAi) affects the diapause proteome of A. franciscana. The proteome was analyzed by shot-gun proteomics coupled to differential isotopic labeling and tandem mass spectrometry. Proteins in the diapause proteome included metabolic enzymes, antioxidants, binding proteins, structural proteins, transporters, translation factors, receptors, and signal transducers. Proteins within the diapause proteome either disappeared or were reduced in amount when p26 was knocked down, or conversely, proteins appeared or increased in amount. Those proteins that disappeared may be p26 substrates, whereas the synthesis of those proteins that appeared or increased may be regulated by p26. This study provides the first global characterization of the diapause proteome of A. franciscana and demonstrates that the sHsp p26 influences proteome composition.

Stress tolerance in diapausing embryos of Artemia franciscana is dependent on heat shock factor 1 (Hsf1)

Embryos of the crustacean, Artemia franciscana, may undergo oviparous development, forming encysted embryos (cysts) that are released from females and enter diapause, a state of suppressed metabolism and greatly enhanced stress tolerance. Diapause-destined embryos of A. franciscana synthesize three small heat shock proteins (sHsps), p26, ArHsp21 and ArHsp22, as well as artemin, a ferritin homologue, all lacking in embryos that develop directly into nauplii. Of these diapause-specific molecular chaperones, p26 and artemin are important contributors to the extraordinary stress tolerance of A. franciscana cysts, but how their synthesis is regulated is unknown. To address this issue, a cDNA for heat shock factor 1 (Hsf1), shown to encode a protein similar to Hsf1 from other organisms, was cloned from A. franciscana. Hsf1 was knocked down by RNA interference (RNAi) in nauplii and cysts of A. franciscana. Nauplii lacking Hsf1 died prematurely upon release from females, showing that this transcription factor is essential to the survival of nauplii. Diapause cysts with diminished amounts of Hsf1 were significantly less stress tolerant than cysts containing normal levels of Hsf1. Moreover, cysts deficient in Hsf1 possessed reduced amounts of p26, ArHsp21, ArHsp22 and artemin, revealing dependence on Hsf1 for expression of their genes and maximum stress tolerance. The results demonstrate an important role for Hsf1, likely in concert with other transcription factors, in the survival and growth of A. franciscana and in the developmentally regulated synthesis of proteins responsible for the stress tolerance of diapausing A. franciscana cysts.

An inter-subunit disulfide bond of artemin acts as a redox switch for its chaperone-like activity

Encysted embryos of Artemia are among the most stress-resistant eukaryotes partly due to the massive amount of a cysteine-rich protein termed artemin. High number of cysteine residues in artemin and their intramolecular spatial positions motivated us to investigate the role of the cysteine residues in the chaperone-like activity of artemin. According to the result of Ellman's assay, there are nine free thiols (seven buried and two exposed) and one disulfide bond per monomer of artemin. Subsequent theoretical analysis of the predicted 3D structure of artemin confirmed the data obtained by the spectroscopic study. Native and reduced/modified forms of artemin were also compared with respect to their efficiency in chaperoning activity, tertiary structure, and stability. Since the alkylation and reduction of artemin diminished its chaperone activity, it appears that its chaperoning potential depends on the formation of intermolecular disulfide bond and the presence of cysteine residues. Comparative fluorescence studies on the structure and stability of the native and reduced protein revealed some differences between them. Due to the redox-dependent functional switching of artemin from the less to more active form, it can be finally suggested as a redox-dependent chaperone.

The Molecular Chaperone Artemin Efficiently Blocks Fibrillization of TAU Protein In Vitro

Objective

Aggregation of the TAU proteins in the form of neurofibrillary tangles (NFTs) in the brain is a common risk factor in tauopathies including Alzheimer’s disease (AD). Several strategies have been implemented to target NFTs, among which chaperones, which facilitate the proper folding of proteins, appear to hold great promise in effectively inhibiting TAU polymerization. The aim of this study was to analyze the impact of the chaperone Artemin on TAU aggregation in vitro.

Materials and Methods

In this experimental study, recombinant TAU- or Artemin proteins were expressed in E.coli bacteria, and purified using ion-exchange and affinity chromatography. Sodium dodecyl sulfate-poly acrylamide gel electrophoresis (SDS-PAGE) was used to run the extracted proteins and check their purity. Heparin was used as an aggregation inducer. The interaction kinetics of TAU aggregation and disassembly was performed using thioflavin T (ThT) fluorescence analysis and circular dichroism (CD) spectroscopy.

Results

Ion-exchange and affinity chromatography yielded highly pure TAU and Artemin proteins for subsequent analyses. In addition, we found that heparin efficiently induced TAU fibrillization 48 hours post-incubation, as evidenced by ThT assay. Importantly, Artemin was observed to effectively block the aggregation of both physiologic- and supra- physiologic TAU concentrations in a dose-dependent manner, as judged by ThT and CD spectroscopy analyses.

Conclusion

Our collective results show, for the first time, that the chaperone Artemin could significantly inhibit aggregation of the TAU proteins in a dose-dependent manner, and support Artemin as a potential potent blocker of TAU aggregation in people with AD.

NMR-based untargeted metabolomic study of hydrogen peroxide-induced development and diapause termination in brine shrimp

Artemia diapause has been extensively studied in embryonic biology for a long time. It has been demonstrated that hydrogen peroxide (H₂O₂) can increase the hatching rate in the development and diapause termination of Artemia cysts. This study used an untargeted ¹H NMR-based metabolomic approach to explore the physiological regulation of H₂O₂ in initiating the development and terminating the diapause of Artemia cysts. This experiment was divided into two parts. In the first part, we analyzed three groups with or without H₂O₂ as control-0h, control-5h and H₂O₂ (180μM)-5h; in the second part, after 7-d incubation, the non-hatching cysts were treated with different H₂O₂ concentrations as low as 180μM and as high 1800μM. The results showed that arginine and proline metabolism were up-regulated after 5h, and H₂O₂ up-regulated valine, leucine and isoleucine biosynthesis in the development of cysts. In the second part, low H₂O₂ (180μM) showed alanine, aspartate and glutamate metabolism, but high H₂O₂ (1800μM) also up-regulated arginine and proline metabolism, as in the control group without H₂O₂ stimulus. These results suggest that enough H₂O₂ can catalyze cell transcription and translation in Artemia cysts, and it improves the cell growth rate, thus allowing embryo cells to grow again.

The avian-specific small heat shock protein HSP25 is a constitutive protector against environmental stresses during blastoderm dormancy

Small heat shock proteins (sHSPs) range in size from 12 to 42 kDa and contain an α-crystalline domain. They have been proposed to play roles in the first line of defence against various stresses in an ATP-independent manner. In birds, a newly oviposited blastoderm can survive several weeks in a dormant state in low-temperature storage suggesting that blastoderm cells are basically tolerant of environmental stress. However, sHSPs in the stress-tolerant blastoderm have yet to be investigated. Thus, we characterised the expression and function of sHSPs in the chicken blastoderm. We found that chicken HSP25 was expressed especially in the blastoderm and was highly upregulated during low-temperature storage. Multiple alignments, phylogenetic trees, and expression in the blastoderms of Japanese quail and zebra finch showed homologues of HSP25 were conserved in other avian species. After knockdown of chicken HSP25, the expression of pluripotency marker genes decreased significantly. Furthermore, loss of function studies demonstrated that chicken HSP25 is associated with anti-apoptotic, anti-oxidant, and pro-autophagic effects in chicken blastoderm cells. Collectively, these results suggest avian HSP25 could play an important role in association with the first line of cellular defences against environmental stress and the protection of future embryonic cells in the avian blastoderm.

Mechanisms of animal diapause: recent developments from nematodes, crustaceans, insects, and fish

Life cycle delays are beneficial for opportunistic species encountering suboptimal environments. Many animals display a programmed arrest of development (diapause) at some stage(s) of their development, and the diapause state may or may not be associated with some degree of metabolic depression. In this review, we will evaluate current advancements in our understanding of the mechanisms responsible for the remarkable phenotype, as well as environmental cues that signal entry and termination of the state. The developmental stage at which diapause occurs dictates and constrains the mechanisms governing diapause. Considerable progress has been made in clarifying proximal mechanisms of metabolic arrest and the signaling pathways like insulin/Foxo that control gene expression patterns. Overlapping themes are also seen in mechanisms that control cell cycle arrest. Evidence is emerging for epigenetic contributions to diapause regulation via small RNAs in nematodes, crustaceans, insects, and fish. Knockdown of circadian clock genes in selected insect species supports the importance of clock genes in the photoperiodic response that cues diapause. A large suite of chaperone-like proteins, expressed during diapause, protects biological structures during long periods of energy-limited stasis. More information is needed to paint a complete picture of how environmental cues are coupled to the signal transduction that initiates the complex diapause phenotype, as well as molecular explanations for how the state is terminated. Excellent examples of molecular memory in post-dauer animals have been documented in Caenorhabditis elegans It is clear that a single suite of mechanisms does not regulate diapause across all species and developmental stages.

Study of model systems to test the potential function of Artemia group 1 late embryogenesis abundant (LEA) proteins

Embryos of the brine shrimp, Artemia franciscana, are genetically programmed to develop either ovoviparously or oviparously depending on environmental conditions. Shortly upon their release from the female, oviparous embryos enter diapause during which time they undergo major metabolic rate depression while simultaneously synthesize proteins that permit them to tolerate a wide range of stressful environmental events including prolonged periods of desiccation, freezing, and anoxia. Among the known stress-related proteins that accumulate in embryos entering diapause are the late embryogenesis abundant (LEA) proteins. This large group of intrinsically disordered proteins has been proposed to act as molecular shields or chaperones of macromolecules which are otherwise intolerant to harsh conditions associated with diapause. In this research, we used two model systems to study the potential function of the group 1 LEA proteins from Artemia. Expression of the Artemia group 1 gene (AfrLEA-1) in Escherichia coli inhibited growth in proportion to the number of 20-mer amino acid motifs expressed. As well, clones of E. coli, transformed with the AfrLEA-1 gene, expressed multiple bands of LEA proteins, either intrinsically or upon induction with isopropyl-β-thiogalactoside (IPTG), in a vector-specific manner. Expression of AfrLEA-1 in E. coli did not overcome the inhibitory effects of high concentrations of NaCl and KCl but modulated growth inhibition resulting from high concentrations of sorbitol in the growth medium. In contrast, expression of the AfrLEA-1 gene in Saccharomyces cerevisiae did not alter the growth kinetics or permit yeast to tolerate high concentrations of NaCl, KCl, or sorbitol. However, expression of AfrLEA-1 in yeast improved its tolerance to drying (desiccation) and freezing. Under our experimental conditions, both E. coli and S. cerevisiae appear to be potentially suitable hosts to study the function of Artemia group 1 LEA proteins under environmentally stressful conditions.

Stress tolerance during diapause and quiescence of the brine shrimp, Artemia

Oviparously developing embryos of the brine shrimp, Artemia, arrest at gastrulation and are released from females as cysts before entering diapause, a state of dormancy and stress tolerance. Diapause is terminated by an external signal, and growth resumes if conditions are permissible. However, if circumstances are unfavorable, cysts enter quiescence, a dormant stage that continues as long as adverse conditions persist. Artemia embryos in diapause and quiescence are remarkably resistant to environmental and physiological stressors, withstanding desiccation, cold, heat, oxidation, ultraviolet radiation, and years of anoxia at ambient temperature when fully hydrated. Cysts have adapted to stress in several ways; they are surrounded by a rigid cell wall impermeable to most chemical compounds and which functions as a shield against ultraviolet radiation. Artemia cysts contain large amounts of trehalose, a non-reducing sugar thought to preserve membranes and proteins during desiccation by replacing water molecules and/or contributing to vitrification. Late embryogenesis abundant proteins similar to those in seeds and other anhydrobiotic organisms are found in cysts, and they safeguard cell organelles and proteins during desiccation. Artemia cysts contain abundant amounts of p26, a small heat shock protein, and artemin, a ferritin homologue, both ATP-independent molecular chaperones important in stress tolerance. The evidence provided in this review supports the conclusion that it is the interplay of these protective elements that make Artemia one of the most stress tolerant of all metazoan organisms.

Group 1 LEA proteins contribute to the desiccation and freeze tolerance of Artemia franciscana embryos during diapause

Water loss either by desiccation or freezing causes multiple forms of cellular damage. The encysted embryos (cysts) of the crustacean Artemia franciscana have several molecular mechanisms to enable anhydrobiosis-life without water-during diapause. To better understand how cysts survive reduced hydration, group 1 late embryogenesis abundant (LEA) proteins, hydrophilic unstructured proteins that accumulate in the stress-tolerant cysts of A. franciscana, were knocked down using RNA interference (RNAi). Embryos lacking group 1 LEA proteins showed significantly lower survival than control embryos after desiccation and freezing, or freezing alone, demonstrating a role for group 1 LEA proteins in A. franciscana tolerance of low water conditions. In contrast, regardless of group 1 LEA protein presence, cysts responded similarly to hydrogen peroxide (H2O2) exposure, indicating little to no function for these proteins in diapause termination. This is the first in vivo study of group 1 LEA proteins in an animal and it contributes to the fundamental understanding of these proteins. Knowing how LEA proteins protect A. franciscana cysts from desiccation and freezing may have applied significance in aquaculture, where Artemia is an important feed source, and in the cryopreservation of cells for therapeutic applications.

Intracellular localization of group 3 LEA proteins in embryos of Artemia franciscana

Late embryogenesis abundant (LEA) proteins are accumulated by anhydrobiotic organisms in response to desiccation and improve survivorship during water stress. In this study we provide the first direct evidence for the subcellular localizations of AfrLEA2 and AfrLEA3m (and its subforms) in anhydrobiotic embryos of Artemia franciscana. Immunohistochemistry shows AfrLEA2 to reside in the cytoplasm and nucleus, and the four AfrLEA3m proteins to be localized to the mitochondrion. Cellular locations are supported by Western blots of mitochondrial, nuclear and cytoplasmic fractions. The presence of LEA proteins in multiple subcellular compartments of A. franciscana embryos suggests the need to protect biological structures in many areas of a cell in order for an organism to survive desiccation stress, and may explain in part why a multitude of different LEA proteins are expressed by a single organism.

Three Heat Shock Protein Genes from Bactrocera (Tetradacus) minax Enderlein: Gene Cloning, Characterization, and Association with Diapause

Bactrocera (Tetradacus) minax Enderlein is a major pest to wild and cultivated species of citrus. Bactrocera minax produces one generation per year with a long pupal diapause period of over 6 months, which hinders efforts to obtain vast numbers of insects under standard room conditions. Determining the mechanisms of diapause is significantly important for obtaining large quantities of these insects. To characterize the heat shock protein (Hsp) genes of B. minax and to unravel their potential contribution to diapause, we performed 3' and 5' RACE to isolate the complementary DNA (cDNA) sequences, bioinformatics to examine the phylogenetic relationships, and real-time quantitative PCR to detect the expression patterns of three Hsp genes during various developmental stages. These results represent the first characterization of the three Hsp genes of B. minax; the open reading frames of Bmhsp23, Bmhsp70, and Bmhsp90 were 510, 1,911, and 1,089 bp, encoding 170, 636, and 363 amino acids, respectively. BmHsp70 and BmHsp90 displayed high identity to previously identified Hsp70 and Hsp90 genes, respectively. BmHsp23 displayed varying similarity, from 28 to 83%, to previously identified small Hsps. Bmhsp23 messenger RNA (mRNA) expression was found to be upregulated during diapause initiation, maintenance, and termination. Bmhsp70 mRNA expression peaked during diapause initiation. Bmhsp90 mRNA expression remained at a relatively low level during deep diapause. Our present results suggest that Bmhsp70 might play an important role in diapause initiation, while Bmhsp23 in diapause initiation and maintenance and Bmhsp90 in diapause regulation. These results improve our understanding of the mechanism of diapause in B. minax at the molecular level.

Quantification of cellular protein expression and molecular features of group 3 LEA proteins from embryos of Artemia franciscana

Late embryogenesis abundant (LEA) proteins are highly hydrophilic, low complexity proteins whose expression has been correlated with desiccation tolerance in anhydrobiotic organisms. Here, we report the identification of three new mitochondrial LEA proteins in anhydrobiotic embryos of Artemia franciscana, AfrLEA3m_47, AfrLEA3m_43, and AfrLEA3m_29. These new isoforms are recognized by antibody raised against recombinant AfrLEA3m, the original mitochondrial-targeted LEA protein previously reported from these embryos; mass spectrometry confirms all four proteins share sequence similarity. The corresponding messenger RNA (mRNA) species for the four proteins are readily amplified from total complementary DNA (cDNA) prepared from embryos. cDNA sequences of the four mRNAs are quite similar, but each has a stretch of sequence that is absent in at least one of the others, plus multiple single base pair differences. We conclude that all four mitochondrial LEA proteins are products of independent genes. Each possesses a mitochondrial targeting sequence, and indeed Western blots performed on extracts of isolated mitochondria clearly detect all four isoforms. Based on mass spectrometry and sodium dodecyl sulfate polyacrylamide gel electrophoresis migration, the cytoplasmic-localized AfrLEA2 exists primarily as a homodimer in A. franciscana. Quantification of protein expression for AfrLEA2, AfrLEA3m, AfrLEA3m_43, and AfrLEA3m_29 as a function of development shows that cellular concentrations are highest in diapause embryos and decrease during development to low levels in desiccation-intolerant nauplius larvae. When adjustment is made for mitochondria matrix volume, the effective concentrations of cytoplasmic versus mitochondrial group 3 LEA proteins are similar in vivo, and the values provide guidance for the design of in vitro functional studies with these proteins.

Artemin, a diapause-specific chaperone, contributes to the stress tolerance of Artemia franciscana cysts and influences their release from females

Females of the crustacean Artemia franciscana produce either motile nauplii or gastrula stage embryos enclosed in a shell impermeable to nonvolatile compounds and known as cysts. The encysted embryos enter diapause, a state of greatly reduced metabolism and profound stress tolerance. Artemin, a diapause-specific ferritin homolog in cysts has molecular chaperone activity in vitro. Artemin represents 7.2% of soluble protein in cysts, approximately equal to the amount of p26, a small heat shock protein. However, there is almost twice as much artemin mRNA in cysts as compared with p26 mRNA, suggesting that artemin mRNA is translated less efficiently. RNA interference employing the injection of artemin double-stranded RNA into the egg sacs of A. franciscana females substantially reduced artemin mRNA and protein in cysts. Decreasing artemin diminished desiccation and freezing tolerance of cysts, demonstrating a role for this protein in stress resistance. Knockdown of artemin increased the time required for complete discharge of a brood of cysts carried within a female from a few hours up to 4 days, an effect weakened in successive broods. Artemin, an abundant molecular chaperone, contributes to stress tolerance of A. franciscana cysts while influencing their development and/or exit from females.

Functional differentiation of small heat shock proteins in diapause-destined Artemia embryos

Encysted embryos of Artemia franciscana cease development and enter diapause, a state of metabolic suppression and enhanced stress tolerance. The development of diapause-destined Artemia embryos is characterized by the coordinated synthesis of the small heat shock proteins (sHsps) p26, ArHsp21 and ArHsp22, with the latter being stress inducible in adults. The amounts of sHsp mRNA and protein varied in Artemia cysts, suggesting transcriptional and translational regulation. By contrast to p26, knockdown of ArHsp21 by RNA interference had no effect on embryo development. ArHsp21 provided limited protection against stressors such as desiccation and freezing but not heat. ArHsp21 may have a non-essential or unidentified role in cysts. Injection of Artemia adults with amounts of ArHsp22 double-stranded RNA less than those used for other sHsps killed females and males, curtailing the analysis of ArHsp22 function in developing embryos and cysts. The results indicate that diapause-destined Artemia embryos synthesize varying amounts of sHsps as a result of differential gene expression and mRNA translation and also suggest that these sHsps have distinctive functions.

Effect of artemin on structural transition of β-lactoglobulin

Encysted embryos of Artemia are exceptionally resistant to severe environmental stress. This resistance is thought to depend in part on the existence of a protein termed artemin. There is only little information about the function of artemin. It has been reported artemin is a thermostable protein with RNA-binding ability. In addition, it reduces the extent of aggregation significantly and enhances the efficiency of refolding and activity recovery of carbonic anhydrase and horseradish peroxidase. In this study, the effect of artemin purified from Artemia urmiana on bovine β-lactoglobulin (BLG) and its α-helical intermediate state has been evaluated by circular dichroism and intrinsic and extrinsic fluorescence spectroscopy. The results obtained in aqueous buffer show, artemin decreases the compactness of BLG structure and causes to the exposure of some hydrophobic groups. The results also indicate artemin has an inhibitory effect on β-sheet→α-helix transition in the secondary structure of β-lactoglobulin. Since this transition occurs during unfolding of β-lactoglobulin, it seems artemin influences on the folding pathway of β-lactoglobulin. This structural effect of artemin can result from its high surface hydrophobicity. Consequently, it is expected that artemin has chaperoning potency because of its effect on the folding of BLG.

Xeroprotectants for the stabilization of biomaterials

With the advancement of science and technology, it is crucial to have effective preservation methods for the stable long-term storage of biological material (biomaterials). As an alternative to cryopreservation, various techniques have been developed, which are based on the survival mechanism of anhydrobiotic organisms. In this sense, it has been found that the synthesis of xeroprotectants can effectively stabilize biomaterials in a dry state. The most widely studied xeroprotectant is trehalose, which has excellent properties for the stabilization of certain proteins, bacteria, and biological membranes. There have also been attempts to apply trehalose to the stabilization of eukaryotic cells but without conclusive results. Consequently, a xeroprotectant or method that is useful for the stable drying of a particular biomaterial might not necessarily be suitable for another one. This article provides an overview of recent advances in the use of new techniques to stabilize biomaterials and compare xeroprotectants with other more standard methods.

Small heat shock protein expression and functions during development

The expression of small heat shock proteins is tightly regulated during development in multiple organisms. As housekeeping proteins, small heat shock proteins help protect cells from apoptosis, stabilize the cytoskeleton and contribute to proteostasis. Consistently, depletion of one small heat shock protein is usually not detrimental due to a certain level of redundancy between the functions of each small heat shock protein. However, while their stress-induced expression is regulated by heat shock factors, their constitutive expression is under the control of other specific transcription factors, suggesting the existence of very specialized functions. This review focuses on the expression patterns and functions of small heat shock proteins in various organisms during development. This article is part of a Directed Issue entitled: Small HSPs in physiology and pathology.

LEA proteins during water stress: not just for plants anymore

Late embryogenesis abundant (LEA) proteins are extremely hydrophilic proteins that were first identified in land plants. Intracellular accumulation is tightly correlated with acquisition of desiccation tolerance, and data support their capacity to stabilize other proteins and membranes during drying, especially in the presence of sugars like trehalose. Exciting reports now show that LEA proteins are not restricted to plants; multiple forms are expressed in desiccation-tolerant animals from at least four phyla. We evaluate here the expression, subcellular localization, biochemical properties, and potential functions of LEA proteins in animal species during water stress. LEA proteins are intrinsically unstructured in aqueous solution, but surprisingly, many assume their native conformation during drying. They are targeted to multiple cellular locations, including mitochondria, and evidence supports that LEA proteins stabilize vitrified sugar glasses thought to be important in the dried state. More in vivo experimentation will be necessary to fully unravel the multiple functional properties of these macromolecules during water stress.

Heat shock protein expression during stress and diapause in the marine copepod Calanus finmarchicus

Calanoid copepods, such as Calanus finmarchicus, are a key component of marine food webs. C. finmarchicus undergo a facultative diapause during juvenile development, which profoundly affects their seasonal distribution and availability to their predators. The current ignorance of how copepod diapause is regulated limits understanding of copepod population dynamics, distribution, and ecosystem interactions. Heat shock proteins (Hsps) are a superfamily of molecular chaperones characteristically upregulated in response to stress conditions and frequently associated with diapause in other taxa. In this study, 8 heat shock proteins were identified in C. finmarchicus C5 copepodids (Hsp21, Hsp22, p26, Hsp90, and 4 forms of Hsp70), and expression of these transcripts was characterized in response to handling stress and in association with diapause. Hsp21, Hsp22, and Hsp70A (cytosolic subfamily) were induced by handling stress. Expression of Hsp70A was also elevated in shallow active copepodids relative to deep diapausing copepodids, which may reflect induction of this gene by varied stressors in active animals. In contrast, expression of Hsp22 was elevated in deep diapausing animals; Hsp22 may play a role both in short-term stress responses and in protecting proteins from degradation during diapause. Expression of most of the Hsps examined did not vary in response to diapause, perhaps because the diapause of C. finmarchicus is not associated with the extreme environmental conditions (e.g., freezing and desiccation) experienced by many other taxa, such as overwintering insects or Artemia cysts.

The structural stability and chaperone activity of artemin, a ferritin homologue from diapause-destined Artemia embryos, depend on different cysteine residues

Diapause-destined embryos of the crustacean, Artemia franciscana, accumulate large amounts of an oligomeric, heat-stable, molecular chaperone termed artemin, a cysteine-enriched ferritin homologue. In this study, cysteines 22, 61, 166, and 172 of artemin were substituted with alanines, respectively yielding ArtC22A, ArtC61A, ArtC166A, and ArtC172A. Wild-type and modified artemins were synthesized in transformed bacteria and purified. As measured by heat-induced denaturation of citrate synthase in vitro, each substitution reduced chaperone activity, with ArtC172A the least active. Protein modeling indicated that C172 is close to a region of surface hydrophobicity, also present in ferritin, suggesting that this site contributes to chaperone activity. Only slight differences in oligomer molecular mass were apparent between artemin variants, but ArtC22A and ArtC61A displayed significantly reduced thermostability, perhaps due to the disruption of an inter-subunit disulphide bridge. In contrast, ArtC172A was thermostable, reflecting the location of C172 on the oligomer surface and that it contributes minimally to artemin stabilization. To our knowledge, this is the initial study of structure/function relationships within a ferritin homologue of importance in diapause and the first to indicate that a defined region of hydrophobicity contributes to artemin and ferritin chaperoning.

Determination in oocytes of the reproductive modes for the brine shrimp Artemia parthenogenetica

The brine shrimp, Artemia, reproduces either oviparously, producing encysted embryos (diapause cysts), or ovoviviparously, producing free-swimming nauplii. Environmental factors, such as photoperiod, have been applied to control the reproduction mode of Artemia, but when the determination of a reproductive mode occurs remains unknown. We analysed the differential gene expression between oocytes from oviparous and ovoviviparous Artemia reared under different photoperiods. A total of 692 qualified cDNA clones were obtained by subtractive hybridization, 327 of which matched GenBank® Nucleotide Sequence Database entries. Gene expressions of 44 cDNAs (representing 56 clones) were analysed in oocytes using real-time PCR. Among these genes, 11 (21 clones) were significantly (P<0.05) up-regulated and 7 (9 clones) down-regulated in Artemia oocytes that subsequently enter diapause. Remarkably, known diapause-related proteins such as ArHsp22 (Artemia heat-shock protein 22) and chitin-binding proteins are found to be already differentially expressed. Furthermore, RNAi (RNA interference) knockdown of a differentially expressed gene, polo-like kinase 1, in oocyte of ovoviviparous Artemia led to the production of white embryos rather than free-swimming nauplii. In summary, our results provide evidence at the molecular level that the reproductive mode of Artemia is already determined at the oocyte stage of their life cycle.

Truncation attenuates molecular chaperoning and apoptosis inhibition by p26, a small heat shock protein from Artemia franciscana

The small heat shock proteins (sHSPs), which prevent irreversible protein denaturation and inhibit apoptosis, consist of an amino-terminus, the canonical α-crystallin domain, and a carboxy-terminal extension. It remains difficult, however, to define sHSP structure-function relationships and with this in mind p26, an sHSP from the crustacean Artemia franciscana, was truncated by deletion mutagenesis. Wild-type p26 cDNA and three truncated variants inserted into the eukaryotic expression vector pcDNA3.1/HisC were used to generate stably transfected 293H cells. p26 shielded transfected cells against death upon exposure to heat and oxidative stress. Truncation reduced chaperone activity, with cells synthesizing the p26 α-crystallin domain being the least resistant. Wild-type p26 inhibited apoptosis in transfected cells, with protection against oxidation-generated apoptosis being more effective than that against heat-induced apoptosis. Truncation reduced p26 apoptotic inhibitory activity, with the α-crystallin domain again being the least effective. The results show that a crustacean sHSP functions effectively in mammalian cells, demonstrating interchangeability of these proteins between distantly related organisms and indicating similarities in their mechanisms of action. Moreover, maximal activity was observed for full-length p26, indicating that structural elements required for chaperone activity and apoptosis inhibition reside throughout the protein.

Diapause termination and development of encysted Artemia embryos: roles for nitric oxide and hydrogen peroxide

Encysted embryos (cysts) of the brine shrimp Artemia undergo diapause, a state of profound dormancy and enhanced stress tolerance. Upon exposure to the appropriate physical stimulus diapause terminates and embryos resume development. The regulation of diapause termination and post-diapause development is poorly understood at the molecular level, prompting this study on the capacity of hydrogen peroxide (H(2)O(2)) and nitric oxide (NO) to control these processes. Exposure to H(2)O(2) and NO, the latter generated by the use of three NO generators, promoted cyst development, emergence and hatching, effects nullified by catalase and the NO scavenger 2-phenyl-4,4,5,5,-tetramethylimidazoline-1-oxyl 3-oxide (PTIO). The maximal effect of NO and H(2)O(2) on cyst development was achieved by 4 h of exposure to either chemical. NO was effective at a lower concentration than H(2)O(2) but more cysts developed in response to H(2)O(2). Promotion of development varied with incubation conditions, indicating for the first time a population of Artemia cysts potentially arrested in post-diapause and whose development was activated by either H(2)O(2) or NO. A second cyst sub-population, refractory to hatching after prolonged incubation, was considered to be in diapause, a condition broken by H(2)O(2) but not NO. These observations provide clues to the molecular mechanisms of diapause termination and development in Artemia, while enhancing the organism's value in aquaculture by affording a greater understanding of its growth and physiology.

Gene expression, metabolic regulation and stress tolerance during diapause

Diapause entails molecular, physiological and morphological remodeling of living animals, culminating in a dormant state characterized by enhanced stress tolerance. Molecular mechanisms driving diapause resemble those responsible for biochemical processes in proliferating cells and include transcriptional, post-transcriptional and post-translational processes. The results are directed gene expression, differential mRNA and protein accumulation and protein modifications, including those that occur in response to changes in cellular redox potential. Biochemical pathways switch, metabolic products change and energy production is adjusted. Changes to biosynthetic activities result for example in the synthesis of molecular chaperones, late embryogenesis abundant (LEA) proteins and protective coverings, all contributing to stress tolerance. The purpose of this review is to consider regulatory and mechanistic strategies that are potentially key to metabolic control and stress tolerance during diapause, while remembering that organisms undergoing diapause are as diverse as the processes itself. Some of the parameters described have well-established roles in diapause, whereas the evidence for others is cursory.

How do animal mitochondria tolerate water stress?

The vast majority of animal species do not tolerate severe water stress, but the encysted embryo of the brine shrimp Artemia franciscana is an exceptionally useful organism to investigate physiological mechanisms for enduring extreme environmental insults. Any substantial reduction in cellular water poses a threat to survival. Nevertheless anhydrobiotic animals survive virtually complete loss of cellular water. The mechanisms that govern "life without water" (anhydrobiosis) are still not well understood. With certain exceptions, it seems that a recurring strategy for tolerating severe water loss involves the accumulation of both low molecular weight solutes (e.g., trehalose or other polyol) and highly hydrophilic macromolecules such as late embryogenesis abundant (LEA) proteins, which were first described about 20 years ago in plant seeds. New studies show that LEA proteins found in animals not only protect proteins in the cytosol during desiccation, but also confer resistance to water stress, including freeze tolerance, to the mitochondrion.

Ametabolic embryos of Artemia franciscana accumulate DNA damage during prolonged anoxia

Encysted embryos of the brine shrimp Artemia franciscana are able to survive prolonged periods of anoxia even when fully hydrated. During this time there is no metabolism, raising the question of how embryos tolerate spontaneous, hydrolytic DNA damage such as depurination. When incubated at 28 degrees C and 40 degrees C for several weeks, hydrated anoxic embryos were found to accumulate abasic sites in their DNA with k=5.8x10(-11) s(-1) and 2.8x10(-10) s(-1), respectively. In both cases this is about 3-fold slower than expected from published observations on purified DNA. However, purified calf thymus DNA incubated under similar anoxic conditions at pH 6.3, the intracellular pH of anoxic cysts, also depurinated more slowly than predicted (about 1.7-fold), suggesting that cysts may in fact accumulate abasic sites only slightly more slowly than purified DNA. Upon reoxygenation of cysts stored under N(2) for 30 weeks at 28 degrees C, the number of abasic sites per 10(4) bp DNA fell from 21.1+/-4.0 to 9.8+/-2.0 by 12 h and to 6.2+/-2.1 by 24 h. Larvae hatched after 48 h and 72 h had only 0.59+/-0.17 and 0.48+/-0.07 abasic sites per 10(4) bp, respectively, suggesting that repair of these lesions had largely taken place before hatching commenced. Thus, unlike bacterial spores, Artemia cysts appear to have no specific protective mechanism beyond what might be afforded by chromatin structure to limit spontaneous depurination, and rely on the repair of accumulated lesions during the period between reoxygenation and hatching.

Occurrence of mitochondria-targeted Late Embryogenesis Abundant (LEA) gene in animals increases organelle resistance to water stress

Anhydrobiotic animals survive virtually complete loss of cellular water. The mechanisms that explain this phenomenon are not fully understood but often include the accumulation of low molecular weight solutes such as trehalose and macromolecules like Late Embryogenesis Abundant (LEA) proteins. Here we report for the first time the occurrence of a mitochondria-targeted LEA gene (Afrlea3m) product in an animal species. The deduced molecular mass of the 307-amino acid polypeptide from the brine shrimp Artemia franciscana is 34 kDa. Bioinformatic analyses reveal features typical of a Group 3 LEA protein, and subcellular localization programs predict targeting of the mature peptide to the mitochondrial matrix, based on an N-terminal, amphipathic presequence. Real-time quantitative PCR shows that Afralea3m mRNA is expressed manyfold higher in desiccation-tolerant embryonic stages when compared with intolerant nauplius larvae. Mitochondrial localization of the protein was confirmed by transfection of human hepatoma cells (HepG2/C3A) with a nucleotide construct encoding the first 70 N-terminal amino acids of AfrLEA3m in-frame with the nucleotide sequence for green fluorescence protein. The chimeric protein was readily incorporated into mitochondria of these cells. Successful targeting of a protein to human mitochondria by use of an arthropod signaling sequence clearly reveals the highly conserved nature of such presequences, as well as of the import machinery. Finally, mitochondria isolated from A. franciscana embryos, which naturally contain AfrLEA3m and trehalose, exhibit resistance to water stress (freezing) as evidenced by an unchanged capacity for oxidative phosphorylation on succinate + rotenone, a resistance that is absent in mammalian mitochondria lacking AfrLEA3m.

The 70 kDa heat shock protein assists during the repair of chilling injury in the insect, Pyrrhocoris apterus

BACKGROUND

The Pyrrhocoris apterus (Insecta: Heteroptera) adults attain high levels of cold tolerance during their overwintering diapause. Non-diapause reproducing adults, however, lack the capacity to express a whole array of cold-tolerance adaptations and show relatively low survival when exposed to sub-zero temperatures. We assessed the competence of non-diapause males of P. apterus for responding to heat- and cold-stresses by up-regulation of 70 kDa heat shock proteins (Hsps) and the role of Hsps during repair of heat- and cold-induced injury.

PRINCIPAL FINDINGS

The fragments of P. apterus homologues of Hsp70 inducible (PaHsp70) and cognate forms (PaHsc70) were cloned and sequenced. The abundance of mRNA transcripts for the inducible form (qPCR) and corresponding protein (Western blotting) were significantly up-regulated in response to high and low temperature stimuli. In the cognate form, mRNA was slightly up-regulated in response to both stressors but very low or no up-regulation of protein was apparent after heat- or cold-stress, respectively. Injection of 695 bp-long Pahsp70 dsRNA (RNAi) caused drastic suppression of the heat- and cold-stress-induced Pahsp70 mRNA response and the up-regulation of corresponding protein was practically eliminated. Our RNAi predictably prevented recovery from heat shock and, in addition, negatively influenced repair of chilling injuries caused by cold stress. Cold tolerance increased when the insects were first exposed to a mild heat shock, in order to trigger the up-regulation of PaHsp70, and subsequently exposed to cold stress.

CONCLUSION

Our results suggest that accumulation of PaHsp70 belongs to a complex cold tolerance adaptation in the insect Pyrrhocoris apterus.