The Mechanism of Low-Temperature Tolerance in Fish

Cloning of down-regulated genes under cold stress and identification of important genes related to cold tolerance in zebrafish (Danio rerio)

Low-temperature stress poses a significant risk to the survival of both cultivated and wild fish populations. Existing studies have found that the pre-acclimation of fishes to moderate cold stress can stimulate the activation of acclimation pathways, thereby enhancing their tolerance to cold stress. The fitness of fish relies heavily on appropriately controlled transcriptional reactions to environmental changes. Despite previous characterization of gene expression profiles in various fish species during cold acclimation, the specific genes responsible for essential functions in this process remain largely unknown, particularly the down-regulated genes induced by cold acclimation. To investigate the genes involved in cold acclimation, this study employed real-time quantitative PCR (RT-qPCR), molecular cloning, microinjection techniques, and cold stress experiments to determine the genes that play an essential part in cold acclimation. Consequently, 18 genes were discovered to be down-regulated in larval zebrafish experiencing cold stress. All 18 genes successfully detected overexpression in zebrafish at 96 and 126 hpf (fold change ≥3), which declined with the growth of zebrafish. Following microinjection, it was observed that her8a, cyp51, lss, txnipb, and bhlha9 had an adverse impact on the survival rate of zebrafish larvae under cold stress. These genes have been identified to play significant roles in various biological processes. For instance, bhlha9 has been found to be involved in both limb development and temperature sensing and her8a has been implicated in neural development. Additionally, cyp51 and lss have been identified as participants in the cholesterol synthesis pathway. Txnipb has been reported to induce cell apoptosis, thereby potentially influencing the survival rate of zebrafish larvae under cold stress. These findings offered crucial data for the analysis of molecular processes related to cold tolerance and the development of cold-resistant fish breeding.

Acclimation during Embryogenesis Remodulates Telomerase Activity and Gene Expression in Baikal Whitefish Larvae, Mitigating the Effects of Acute Temperature Stress

Acclimation through the hormesis effect increases the plasticity of organisms, which has been shown for many ectothermic animals, including fish. We investigated the effect of temperature acclimation in Baikal whitefish Coregonus baicalensis (Dybowski, 1874). Telomere length, telomerase activity, and the expression of genes, whose products are involved in the regulation of telomere length and defense against reactive oxygen species, were selected to assess the state of the larvae. Acclimation and acute temperature stress (+12 °C) had no effect on telomere length, but altered telomerase activity (acclimation decreased it; stress increased it) and the levels of genes expression. Under stress, the expression of superoxide dismutase genes was increased in acclimated larvae and that of glutathione peroxidases in non-acclimated larvae, which may indicate lower reactive oxygen species formation and slower antioxidant responses in acclimated fish. The expression of some telomere-related genes was reduced under temperature stress, but the expression of the tzap and smg genes, whose products improve the control of telomere length by preventing them from lengthening or shortening, was increased in acclimated individuals. The data obtained indicate a positive effect of acclimation on the state of the Baikal whitefish larvae by remodulation of their telomerase activity and the transcriptional profile.

Effects of cold acclimation on serum biochemical parameters and metabolite profiles in Schizothorax prenanti

BACKGROUND

Environmental temperature is critical in regulating biological functions in fish. S. prenanti is a kind of cold-water fish, but of which we have little knowledge about the metabolic adaptation and physiological responses to long-term cold acclimation.

RESULTS

In this study, we determined the physiological responses of S. prenanti serum after 30 days of exposure to 6℃. Compared with the control group, the levels of TC, TG, and LDL-C in the serum were significantly (P < 0.05) increased, and the level of glucose was significantly (P < 0.05) decreased under cold acclimation. Cold acclimation had no effect on the gene expression of pro-inflammatory factors and anti-inflammatory factors of S. prenanti. Metabolomics analysis by LC-MS showed that a total of 60 differential expressed metabolites were identified after cold acclimation, which involved in biosynthesis of amino acids, biosynthesis of unsaturated fatty acids, steroid degradation, purine metabolism, and citrate cycle pathways.

CONCLUSION

The results indicate that cold acclimation can alter serum metabolites and metabolic pathways to alter energy metabolism and provide insights for the physiological regulation of cold-water fish in response to cold acclimation.

Integrated 4D label-free proteomics and data mining to elucidate the effects of thermal processing on crisp grass carp protein profiles

The crisp grass carp (CGC; Ctenopharyngodon idellus C. et V.), known for its unique texture and flavour, is a culinary delicacy whose quality is significantly influenced by thermal processing. This study employed 4D label-free proteomics and data mining techniques to investigate the proteomic changes in CGC muscle tissue induced by various heating temperatures. CGC samples were subjected to a series of heat treatments at increasing temperatures from 20 °C to 90 °C. Proteins were extracted, digested, and analysed using high-resolution mass spectrometry. The proteomic data were then subjected to extensive bioinformatics analysis, including GO and KEGG pathway enrichment. We identified a total of 1085 proteins, 516 of which were shared across all the temperature treatments, indicating a core proteome responsible for CGC textural properties. Differential expression analysis revealed temperature-dependent changes, with significant alterations observed at 90 °C, suggesting denaturation or aggregation of proteins at higher temperatures. Functional enrichment analysis indicated that proteins involved in amino acid metabolism, glutathione metabolism, and nucleotide metabolism were particularly affected by heat. Textural analysis correlated these proteomic changes with alterations in CGC quality attributes, pinpointing 70 °C as the optimum temperature for maintaining the desired texture. A strong positive correlation between specific upregulated proteins was identified, such as the tubulin alpha chain and collagen alpha-1(IV) chain, and the improved textural properties of CGC during thermal processing, suggesting their potential as the potential biomarkers. This study offers a comprehensive proteomic view of the thermal stability and functionality of CGC proteins, delivering invaluable insights for both the culinary processing and scientific management of CGC. Our findings not only deepen the understanding of the molecular mechanisms underpinning the textural alterations in CGC during thermal processing but also furnish practical insights for the aquaculture industry. These insights could be leveraged to optimize cooking techniques, thereby enhancing the quality and consumer appeal of CGC products.

Physiological, metabolomic, and transcriptomic reveal metabolic pathway alterations in Gymnocypris przewalskii due to cold exposure

Teleost fish have evolved various adaptations that allow them to tolerate cold water conditions. However, the underlying mechanism of this adaptation is poorly understood in Tibetan Plateau fish. RNA-seq combined with liquid chromatography‒mass spectrometry (LC‒MS/MS) metabolomics was used to investigate the physiological responses of a Tibetan Plateau-specific teleost, Gymnocypris przewalskii, under cold conditions. The 8-month G. przewalskii juvenile fish were exposed to cold (4 ℃, cold acclimation, CA) and warm (17 ℃, normal temperature, NT) temperature water for 15 days. Then, the transcript profiles of eight tissues, including the brain, gill, heart, intestine, hepatopancreas, kidney, muscle, and skin, were evaluated by transcriptome sequencing. The metabolites of the intestine, hepatopancreas, and muscle were identified by LC‒MS/MS. A total of 5,745 differentially expressed genes (DEGs) were obtained in the CA group. The key DEGs were annotated using Gene Ontology and Kyoto Encyclopedia of Genes and Genomes analysis. The DEGs from the eight tissues were significantly enriched in spliceosome pathways, indicating that activated alternative splicing is a critical biological process that occurs in the tissues to help fish cope with cold stress. Additionally, 82, 97, and 66 differentially expressed metabolites were identified in the intestine, hepatopancreas, and muscle, respectively. Glutathione metabolism was the only overlapping significant pathway between the transcriptome and metabolome analyses in these three tissues, indicating that an activated antioxidative process was triggered during cold stress. In combination with the multitissue transcriptome and metabolome, we established a physiology-gene‒metabolite interaction network related to energy metabolism during cold stress and found that gluconeogenesis and long-chain fatty acid metabolism played critical roles in glucose homeostasis and energy supply.

Fatty acid metabolism and antioxidant capacity in Gymnocypris przewalskii (Kessler, 1876) response to thermal stress

The Qinghai-Tibet Plateau is undergoing a wet-warming transition, which could affect the survival of the native fish. However, the tolerance and physiological response to thermal stress is rarely studied in Gymnocypris przewalskii, a rare native fish in the Tibetan plateau. In this study, first, we detected the thermal tolerance of five groups of six-month G. przewalskii which acclimated at 8, 12, 16, 20, and 24 °C for two weeks, respectively, by critical thermal methodology. Then, through heat challenge, we detected the metabolites, key enzyme activities, and gene expressions involved in metabolism and antioxidant in the hepatopancreas when the temperatures increased from 16 °C to 18, 20, 22, 24, 26, and 28 °C for 12 h, respectively. The results showed that although the fish are sensitive to high temperatures, the quick acclimation at mild high temperatures could significantly improve the tolerance to acute high-temperature stress in juvenile G. przewalskii. During the heat challenge study, blood glucose significantly increased at heat stress (P < 0.05). At the same time, total cholesterol (TC), triglyceride (TG), and free fatty acid (FFA) significantly decreased when the temperature rose continuously to 20 °C. Metabolic enzyme activities of carnitine palmityl transferase I (CPT-Ⅰ), acetyl-CoA carboxylase (ACC), and fatty acid synthase (FAS) significantly decreased at 20 °C (P < 0.05). Superoxide dismutase (SOD) and antioxidant capacity (T-AOC) significantly increased at 20 °C (P < 0.05). The relative transcript levels of genes involved in antioxidant and glycolysis/gluconeogenesis were markedly higher than the control at 20-26 °C (P < 0.05). The genes involved in fatty acid biosynthesis or metabolism showed different expression patterns under heat stress. Heat shock protein 70 (Hsp70) and Hsp90 were significantly higher than the control at 18 °C and 26 °C, respectively. These results confirmed the prediction that G. przewalskii is sensitive to high temperatures, so conservation efforts should pay more attention to the warming damage.

Rising floor and dropping ceiling: organ heterogeneity in response to cold acclimation of the largest extant amphibian

Low temperature imposes strong selective pressure on ectotherms. To maximize their overall fitness under cold conditions, the ectotherms may either try to maintain their physiological activities through metabolic compensation or enter into metabolic depression; however, some species adopt both strategies to cope with different degrees of cold. Nevertheless, how these two seemingly opposite strategies are coordinated has rarely been elucidated. Here, we investigated the molecular strategy underlying the cold acclimation of Andrias davidianus, the largest extant amphibian, using multi-organ metabolomics and transcriptomics. The results showed remarkable organ heterogeneity in response to cold. While most organs showed transcriptional upregulation of metabolic processes, the heart exhibited downregulation. This heterogeneity explained the adaptive reorganization in resource allocation, which compensates for metabolic maintenance by compromising growth. Importantly, the cardiac function might constitute a 'ceiling' to constrain the space for compensation, especially under colder conditions. Additionally, the opposite transcriptional regulation of oxidative phosphorylation and other pathways might also shape the overall metabolic capacity under cold conditions. The heterogeneity in cold responses may have directed a shift in cold adaptive strategy from compensation to depression with a drop in temperature. These results provide a novel insight into the regulatory mechanisms underlying cold survival strategies of ectotherms.

Use of acellular intact fish skin grafts in treating acute paediatric wounds during the COVID-19 pandemic: a case series

Objective:

More specific strategies are needed to support children requiring skin grafting. Our goal was to identify procedures that reduce operating times, post-operative complications, pain and length of hospital stay. Patient safety, optimal wound bed support and quick micro-debridement with locoregional anaesthesia were prioritised. Ultimately, a novel acellular fish skin graft (FSG) derived from north Atlantic cod was selected for use.

Method:

We admitted consecutive paediatric patients with various lesions requiring skin grafting for definitive wound closure. All FSGs were applied and bolstered in the operating room following debridement.

Results:

In a cohort of 15 patients, the average age was 8 years and 9 months (4 years 1 month–13 years 5 months). Negative pressure wound therapy (NPWT) was given to 12 patients. Rapid wound healing was observed in all patients, with a wound area coverage of 100% and complete healing in 95% of wounds. Time until engraftment in patients receiving NPWT was reduced by about a half (to an average 12 days) from our standard experience of 21 days. Ten patients received locoregional anaesthesia and were discharged after day surgery. The operating time was <60 minutes, and no complications or allergic reactions were reported. Excellent pliability of the healed wound was achieved in all patients, without signs of itching and scratching in the postoperative period. This case series is the first and largest using FSG to treat paediatric patients with different wound aetiologies. We attribute the rapid transition to acute wound status and the good pliability of the new epidermal–dermal complex to the preserved molecular components of the FSG, including omega-3.

Conclusion:

FSG represents an innovative and sustainable solution for paediatric wound care that results in shorter surgery time and reduced hospital stays, with accelerated wound healing times.

Genome-Wide Association and Expression Analysis Revealed the Candidate Variants and Molecular Underpinnings of Cold-Stress Response in Large Yellow Croaker

Large yellow croaker (Larimichthys crocea) is one of the most economically important fish in China. Recently, global climate change has caused more and more intense and extreme low temperature weathers, resulting in huge losses to the large yellow croaker industry. Therefore, it is essential to understand the mechanisms of low-temperature tolerance in large yellow croaker. Here, we conducted an integrative analysis of genome-wide association study (GWAS) and transcriptome analysis to identify candidate variants and reveal the molecular underpinning of cold-stress response in large yellow croaker. A total of 8 significant single nucleotide polymorphisms (SNPs) loci on 6 chromosomes were identified in the GWAS analysis, and 5764 (gill) and 3588 (liver) differentially expressed genes (DEGs) were detected in cold-stressed large yellow croaker, respectively. Further comparative and functional analysis of the candidate genes and DEGs highlighted the importance of pathways/genes related to immune response, cellular stress response, lipid transport, and metabolism in the cold-stress response of large yellow croaker. Our results provide insights into the cold tolerance of large yellow croaker and contribute to genomic-based selection for low-temperature-resistant large yellow croaker.

Get up early: Revealing behavioral responses of sandeel to ocean warming using commercial catch data

Warming of the oceans and shifts in the timing of annual key events are likely to cause behavioral changes in species showing a high degree of site fidelity. While this is well studied in terrestrial systems, there are fewer examples from the marine environment. Sandeel (Ammodytes marinus) is a small eel-shaped teleost fish with strong behavioral attachment to sandy habitats in which they are buried from late summer through winter. When spring arrives, the sandeel emerge to feed during the day for several of months before returning to the sand for overwintering refuge.Using fisheries data from the North Sea, we investigated whether catch rates reflect the timing of emergence and if seasonal patterns are related to temperature and primary production.Catch per unit effort (CPUE) was used to describe sandeel emergence. We developed indicators of the relative timing of the emergence from the winter sand refuge and the subsequent growth period. Different modeling approaches were used to investigate the relationship with bottom temperature and primary production.Variation in emergence behavior was correlated with variation in sea bottom temperature. Warmer years were characterized by earlier emergence. Significant warming over the last three decades was evident in all sandeel habitats in the North Sea throughout most of their adult life history, though no net shift in the phenology of emergence was detected. Minimum temperature during spring was a better predictor of emergence behavior than, for example, degree days.This study emphasizes how temperature-induced changes in behavior may have implications for predators and fisheries of sandeel. The method can be applied to other species for which the timing of exploitation (i.e., fisheries) and species life history are well matched.

Transcriptome and co-expression network analyses reveal the regulatory pathways and key genes associated with temperature adaptability in the yellow drum (Nibea albiflora)

The yellow drum (Nibea albiflora) is an important marine economy fish, that is widely distributed in the coastal waters of the Northwest Pacific. To understand the molecular regulatory mechanism of the yellow drum under temperature stress, transcriptome analysis was performed under five temperature conditions (10 °C, 15 °C, 20 °C, 24 °C, 28 °C) in the present study. Compared with 20 °C, 163, 401, 276, and 372 differentially expressed genes (DEGs) were obtained at 10 °C, 15 °C, 24 °C and 28 °C, respectively. Gene Ontology (GO) analysis indicated that the DEGs were mainly involved in cellular processes, metabolic processes, catalytic activity, membrane and binding. Meanwhile, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis showed that the temperature adaptive regulation of the yellow drum was mainly involved in signal transduction, metabolism, genetic information and protein processing. Weighted gene co-expression network analysis (WGCNA) showed that HMGB1, STAT4, Noct, C1q and CRT may be the key hub genes in the response of the yellow drum to temperature stress. In addition, 20 genes that may be associated with temperature stress were identified based on comparative analysis between the KEGG enrichment and the WGCNA results. Ten DEGs were selected for further validation using quantitative real-time PCR (qRT-PCR), and the results were consistent with the RNA-seq data. This study explored the transcriptional patterns of the yellow drum under temperature stress and provided fundamental information on the temperature adaptability of this species.

Effects of acute low temperature stress on the hormones and gene expression of glucocorticoid receptor of large yellow croaker Larimichthys crocea

The neuroendocrine system of fish responds to low temperature via regulating hormones. To explore the adaptability of Larimichthys crocea to low temperature, the levels of the plasma cortisol, thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), total cholesterol (TC), and glucose were determined after exposure to low temperature and during subsequent rewarming. Furthermore, the mRNA expression of the glucocorticoid receptor (GR) gene was analyzed under the stress. We found that the levels of the plasma cortisol, TSH, T3, glucose, and TC increased under the low temperature stress, suggesting that elevated hormones may be conducive to promoting the mobilization of the glucose and lipid in L. crocea exposed to low temperature. During the rewarming period, the plasma cortisol level decreased, whereas the T3 level was still significantly higher than that in the control group. Notably, the plasma T4 level was unaffected by the temperature changes. Furthermore, the sequence alignment and phylogenetic tree analysis revealed that the GR protein of L. crocea had high homology and a similar protein structure with those from other teleosts. Under the low temperature stress, the GR mRNA expression increased in the brain and head kidney, whereas it basically returned to the control level following rewarming. These findings revealed the changes of the hormones and the potential function of the GR gene in L. crocea following exposure to low temperature, providing some insights into breeding low temperature-resistant varieties of L. crocea.

Metabolomics analysis of the effects of temperature on the growth and development of juvenile European seabass (Dicentrarchus labrax)

Temperature variations have significant impacts on the growth and development of fish. In this study, the effects of temperature on the growth and development of European seabass (Dicentrarchus labrax) were investigated using ultra-performance liquid chromatography-tandem mass spectrometry-based metabolomics. Three groups of fish were exposed to various temperatures for 60 days: T1-E (10 °C), T2-E (15 °C), and T3-E (20 °C). Afterward, the temperature of all groups was increased to 20 °C and maintained for 62 days (T1-S, T2-S, T3-S). The livers were extracted for subsequent analysis. In the first stage of the experiment, the growth rate was highest in the T3-E group, followed by the T1-E and T2-E groups. The following metabolites identified by comparative analysis were found to be elevated: L-thyroxine, cysteamine, uridine diphosphate (UDP)-glucose, α-ketoglutaric acid, carbamoyl phosphate, and guanidine acetic acid of the T1-E group. Pathway analysis of the altered metabolites suggested changes in glucose metabolism, arginine and proline metabolism, the tricarboxylic acid cycle, the ornithine cycle, histidine metabolism, and taurine metabolism, which were involved with growth and development. Meanwhile, partial compensatory growth was observed in fish in the T1-S and T2-S groups. Metabolites identified as potential markers of growth included L-cysteine, taurocholic acid, UDP-glucose, and L-thyroxine. The significantly changed metabolic pathways were cysteine and methionine metabolism, bile secretion, tyrosine metabolism, and hypotaurine metabolism. We screened out the marker metabolites and metabolic pathway could provide important insights into the potential mechanisms of temperature affects the growth and development of European seabass. All in all, our research can provide theoretical basis and technical guidance for efficiently culturing European seabass.

Phylogenic Determinants of Cardiovascular Frailty, Focus on Hemodynamics and Arterial Smooth Muscle Cells

The evolution of the circulatory system from invertebrates to mammals has involved the passage from an open system to a closed in-parallel system via a closed in-series system, accompanying the increasing complexity and efficiency of life’s biological functions. The archaic heart enables pulsatile motion waves of hemolymph in invertebrates, and the in-series circulation in fish occurs with only an endothelium, whereas mural smooth muscle cells appear later. The present review focuses on evolution of the circulatory system. In particular, we address how and why this evolution took place from a closed, flowing, longitudinal conductance at low pressure to a flowing, highly pressurized and bifurcating arterial compartment. However, although arterial pressure was the latest acquired hemodynamic variable, the general teleonomy of the evolution of species is the differentiation of individual organ function, supported by specific fueling allowing and favoring partial metabolic autonomy. This was achieved via the establishment of an active contractile tone in resistance arteries, which permitted the regulation of blood supply to specific organ activities via its localized function-dependent inhibition (active vasodilation). The global resistance to viscous blood flow is the peripheral increase in frictional forces caused by the tonic change in arterial and arteriolar radius, which backscatter as systemic arterial blood pressure. Consequently, the arterial pressure gradient from circulating blood to the adventitial interstitium generates the unidirectional outward radial advective conductance of plasma solutes across the wall of conductance arteries. This hemodynamic evolution was accompanied by important changes in arterial wall structure, supported by smooth muscle cell functional plasticity, including contractility, matrix synthesis and proliferation, endocytosis and phagocytosis, etc. These adaptive phenotypic shifts are due to epigenetic regulation, mainly related to mechanotransduction. These paradigms actively participate in cardio-arterial pathologies such as atheroma, valve disease, heart failure, aneurysms, hypertension, and physiological aging.

Effects of temperature on feeding and digestive processes in fish

As most fish are ectotherms, their physiology is strongly affected by temperature. Temperature affects their metabolic rate and thus their energy balance and behavior, including locomotor and feeding behavior. Temperature influences the ability/desire of the fish to obtain food, and how they process food through digestion, absorb nutrients within the gastrointestinal tract, and store excess energy. As fish display a large variability in habitats, feeding habits, and anatomical and physiological features, the effects of temperature are complex and species-specific. The effects of temperature depend on the timing, intensity, and duration of exposure as well as the speed at which temperature changes occur. Whereas acute short-term variations of temperature might have drastic, often detrimental, effects on fish physiology, long-term gradual variations might lead to acclimation, e.g. variations in metabolic and digestive enzyme profiles. The goal of this review is to summarize our current knowledge on the effects of temperature on energy homeostasis, with specific focus on metabolism, feeding, digestion, and how fish are often able to "adapt" to changing environments through phenotypic and physiological changes.

Physiological responses to cold and starvation stresses in the liver of yellow drum (Nibea albiflora) revealed by LC-MS metabolomics

As global climate changes, mass mortality in farmed fish associated with the severely cold weather has aroused growing concerns. Yellow drum (Nibea albiflora) is an important maricultured fish in China, whereby its aquaculture suffered from overwinter mortality associated with cold and cold-induced-fasting stresses. Here, by using LC-MS metabolomics combined with transcriptomics, we investigated the physiological responses of yellow drum liver to cold and starvation stresses. The experiment involved four groups: 16 °C fed group (CG1), 16 °C unfed group (CG2), 8 °C fed group (EG1), and 8 °C unfed group (EG2). Under cold stress, a total of 308 and 257 differential metabolites were identified in EG1 vs. CG1 and EG2 vs. CG2, respectively, showing 5 overlapping significant pathways: glutathione metabolism, biosynthesis of unsaturated fatty acids, galactose metabolism, arginine and proline metabolism, and ABC transporters. Intersection analysis identified that glutamate, oxidized glutathione (GSSG), and eicosenoic acid were the common metabolites induced by cold stress. Under starvation stress, a total of 300 and 215 differential metabolites were identified in CG2 vs. CG1 and EG2 vs. EG1, respectively, showing 2 overlapping significant pathways: glutathione metabolism and galactose metabolism. Intersection analysis revealed that glutamate and GSSG were the common metabolites caused by fasting. Under cold and starvation combined stresses, 286 differential metabolites were identified in EG2 vs. CG1, showing 7 influenced pathways: glycerophospholipid metabolism, biosynthesis of unsaturated fatty acids, glutathione metabolism, sphingolipid metabolism, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, autophagy, and purine metabolism. Interestingly, the glutamate and GSSG were induced by both single and combined stresses of cold and starvation treatments. These findings suggest that glutathione metabolism and its related metabolites (glutamate and GSSG) could be potential biomarkers of cold and starvation stresses in yellow drum. Overall, the results of this study provided insights into the physiological regulation in response to cold and starvation stresses in this fish.

Tissue-specific effects of temperature on proteasome function

Variation in ambient growth temperature can cause changes in normal animal physiology and cellular functions such as control of protein homeostasis. A key mechanism for maintaining proteostasis is the selective degradation of polyubiquitinated proteins, mediated by the ubiquitin-proteasome system (UPS). It is still largely unsolved how temperature changes affect the UPS at the organismal level. Caenorhabditis elegans nematodes are normally bred at 20 °C, but for some experimental conditions, 25 °C is often used. We studied the effect of 25 °C on C. elegans UPS by measuring proteasome activity and polyubiquitinated proteins both in vitro in whole animal lysates and in vivo in tissue-specific transgenic reporter strains. Our results show that an ambient temperature shift from 20 to 25 °C increases the UPS activity in the intestine, but not in the body wall muscle tissue, where a concomitant accumulation of polyubiquitinated proteins occurs. These changes in the UPS activity and levels of polyubiquitinated proteins were not detectable in whole animal lysates. The exposure of transgenic animals to 25 °C also induced ER stress reporter fluorescence, but not the fluorescence of a heat shock responsive reporter, albeit detection of a mild induction in hsp-16.2 mRNA levels. In conclusion, C. elegans exhibits tissue-specific responses of the UPS as an organismal strategy to cope with a rise in ambient temperature.

Identification and characterization of miRNAs involved in cold acclimation of zebrafish ZF4 cells

MicroRNAs (miRNAs) play vital roles in various biological processes under multiple stress conditions by leading to mRNA cleavage or translational repression. However, the detailed roles of miRNAs in cold acclimation in fish are still unclear. In the present study, high-throughput sequencing was performed to identify miRNAs from 6 small RNA libraries from the zebrafish embryonic fibroblast ZF4 cells under control (28°C, 30 days) and cold-acclimation (18°C, 30 days) conditions. A total of 414 miRNAs, 349 known and 65 novel, were identified. Among those miRNAs, 24 (19 known and 5 novel) were up-regulated, and 23 (9 known and 14 novel) were down-regulated in cold acclimated cells. The Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analyses indicated that the target genes of known differentially expressed miRNAs (DE-miRNA) are involved in cold acclimation by regulation of phosphorylation, cell junction, intracellular signal transduction, ECM-receptor interaction and so on. Moreover, both miR-100-3p inhibitor and miR-16b mimics could protect ZF4 cells under cold stress, indicating the involvement of miRNA in cold acclimation. Further study showed that miR-100-3p and miR-16b could regulate inversely the expression of their target gene (atad5a, cyp2ae1, lamp1, rilp, atxn7, tnika, btbd9), and that overexpression of miR-100-3p disturbed the early embryonic development of zebrafish. In summary, the present data show that miRNAs are closely involved in cold acclimation in zebrafish ZF4 cells and provide information for further understanding of the roles of miRNAs in cold acclimation in fish.