Cloning and characterization of cDNAs for 70-kDa heat-shock proteins (Hsp70) from two fish species of the genus Oryzias

Genome-wide identification of Hsp70/110 genes in rainbow trout and their regulated expression in response to heat stress

Heat shock proteins (Hsps) play an important role in many biological processes. However, as a typical cold water fish, the systematic identification of Hsp70/110 gene family of rainbow trout (Oncorhynchus mykiss) has not been reported, and the role of Hsp70/110 gene in the evolution of rainbow trout has not been described systematically. In this study, bioinformatics methods were used to analyze the Hsp70/110 gene family of rainbow trout. A total of 16 hsp70/110 genes were identified and classified into ten subgroups. The 16 Hsp70/110 genes were all distributed on chromosomes 2, 4, 8 and 13. The molecular weight is ranged from 78.93 to 91.39 kD. Gene structure and motif composition are relatively conserved in each subgroup. According to RNA-seq analysis of rainbow trout liver and head kidney, a total of four out of 16 genes were significantly upregulated in liver under heat stress, and a total of seven out of 16 genes were significantly upregulated in head kidney. RT-qPCR was carried out on these gene, and the result were consistent with those of RNA-seq. The significantly regulated expressions of Hsp70/110 genes under heat stress indicats that Hsp70/110 genes are involved in heat stress response in rainbow trout. This systematic analysis provided valuable information about the diverse roles of Hsp70/110 in the evolution of teleost, which will contribute to the functional characterization of Hsp70/110 genes in further research.

The Hsp70 Gene Family in Boleophthalmus pectinirostris: Genome-Wide Identification and Expression Analysis under High Ammonia Stress

Simple Summary

Heat shock proteins 70 is a family of proteins, which were expressed in response to a wide range of biotic and abiotic stressors. The development of genomic resources and transcriptome sequences makes it practical to conduct a systematic analysis of these genes. In this study, exhaustive searches of all genomic resources for Boleophthalmus pectinirostris Hsp70 genes were performed and their responses to high environmental ammonia stress were investigated. Besides, selection test was implemented on those duplicated genes, and the phylogenetic tree, gene structure, and motif analysis were also constructed to assign names of them. The result showed that there were 20 Hsp70 genes within the genome of Boleophthalmus pectinirostris, and some sites in the duplicated genes may experience positive selection, and most of Hsp70 genes were downregulated after exposure to high concentration ammonia. The present results of this study can be used as a reference for further biological studies on mudskippers.

Abstract

Heat shock proteins 70 have triggered a remarkable large body of research in various fishes; however, no genome-wide identification and expression analysis has been performed on the Hsp70 gene family of Boleophthalmus pectinirostris. In this study, we identified 20 Hsp70 genes within the genome of B. pectinirostris and provided insights into their response to high environmental ammonia (HEA) stress. Positive selection on stress response genes and expansion of hspa1a and hspa1a-like genes might be related to terrestrial adaptations in this species. The expression patterns of the Hsp70 gene family in the gill and liver of B. pectinirostris under HEA stress were studied by examining transcriptome data. The results showed that most Hsp70 genes were downregulated after high concentration ammonia exposure. The downregulation may be related to the hypoxic condition of the tissues.

Four Members of Heat Shock Protein 70 Family in Korean Rose Bitterling (Rhodeus uyekii)

Heat shock protein (HSP) 70, the highly conserved stress protein families, plays important roles in protecting cells against heat and other stresses in most animal species. In the present study, we identified and characterized four Hsp70 (RuHSP4, RuHSC70, RuHSP12A, RuGRP78) family proteins based on the expressed sequence tag (EST) analysis of the Korean rose bitterling R. uyekii cDNA library. The deduced RuHSP70 family has high amino acid identities of 72-99% with those of other species. Phylogenetic analysis revealed that RuHsp70 family clustered with fish groups (HSP4, HSC70, HSP12A, GRP78) proteins. Quantitative RT-PCR analysis showed the specific expression patterns of RuHsp70 family members in the early developmental stages and several tissues in Korean rose bitterling. The expression of 4 groups of Hsp70 family was detected in all tested tissue. Particularly, Hsp70 family of Korean rose bitterling is highly expressed in hepatopancreas and sexual gonad (testis and ovary). The expression of Hsp70 family was differentially regulated in accordance with early development stage of Rhodeus uyekii.

Cloning, molecular characterization and expression analysis of heat shock cognate 70 (Hsc70) cDNA from turbot (Scophthalmus maximus)

As an essential member of the HSP70 family, heat shock cognate 70 (Hsc70) is a constitutively expressed molecular chaperone involved in protein metabolism. In this paper, turbot Hsc70 was cloned and the expression profile was also analyzed. The full-length cDNA of the turbot Hsc70 was 2,292 bp in length, including a 113-bp 5' UTR, a 223-bp 3' UTR and a 1,956-bp open reading frame coding a protein with 651 amino acid residues. Comparison of amino acid sequence revealed the existence of three classical HSP70 family signature motifs, a signature nonapeptide and one repeat of tetrapeptide in turbot Hsc70. The turbot Hsc70-deduced amino acids sequence exhibited 75.4-96.8 % homology with Hsp70s/Hsc70s of 24 other known sequences. In particular, the strongest homology was found with the cognate members of Hsc70 subfamily and the highest identity was found with Japanese flounder Hsc70. Semi-quantitative RT-PCR revealed that turbot Hsc70 transcripts were stably expressed in all tested tissues under normal physiological condition, while the expression levels also increased (~1.5-fold to ~threefold) after heat shock and bacterial infection. In addition, Hsc70 transcripts were detected throughout embryonic development and in turbot embryonic cell line (TEC) in the absence of any stress. Meanwhile, it was also heat inducible, but not cold inducible in TEC. These results suggest that Hsc70 gene may be involved in embryogenesis and cellular protection events under normal and stress condition.

Cloning and expression analysis of a HSP70 gene from Korean rockfish (Sebastes schlegeli)

The gene encoding HSP70 was isolated from Korean rockfish Sebastes schlegeli by homologous cloning and rapid amplification of cDNA ends (RACE). The full-length of HSP70 cDNA was composed of 2259 bp and encoded a polypeptide of 639 amino acids. BLAST analysis showed that HSP70 of S. schlegeli shared high identities with those of the Lates calcarifer, Oreochromis niloticus, Seriola quinqueradiata HSP70s (88-89%). Our current study also revealed that HSP70 of Korean rockfish was expressed in many tissues by RT-PCR under unstressed condition. Quantitative real-time PCR showed that the expression patterns of Korean rockfish HSP70 were developmental stage-dependency. The expression of HSP70 was measured by quantitative real-time PCR after different oxygen treatments. The results showed that expression of HSP70 increased significantly after exposure to hypoxia for 30 min in gill and ovary, and then decreased for 60 min, and the level in spleen and liver gradually increased and reached the highest at 60 min. In addition, in gill, spleen and liver, the HSP70 mRNA level reached the maximum in hypoxia group after one hour different oxygen concentration stress. Increased amounts of serum thyroxine (T4), and triiodothyronine (T3) were also found during 30 min hypoxia treatment and 60 min normoxia group in our study. All of the results provide information to further study the mechanism of physiology and immune function under stress conditions of ovoviviparous teleosts.

Molecular cloning and expression analysis of heat-shock protein 70 in orange-spotted grouper Epinephelus coioides following heat shock and Vibrio alginolyticus challenge

In this study, the complementary (c)DNA encoding heat-shock protein 70 (Hsp70) of orange-spotted grouper Epinephelus coioides (OsgHsp70) was cloned. OsgHsp70 was 2206 bp and encoded 652 amino acids with predicted molecular mass of 70·89 kDa and theoretical isoelectric point of 5·48. Three Hsp70 family signatures, bipartite nuclear localization signal sequence (NLS) and cytoplasmic characteristic motif (EEVD) were observed in the OsgHsp70, which shared high similarity in amino-acid sequences with the Hsp70 gene of other vertebrates. The results indicated that the OsgHsp70 is a member of the heat-shock protein 70 family. The Hsp70 messenger (m)RNA expressions were quantified by real-time PCR following heat shock, bacterial infection and immunization with formalin-killed Vibrio alginolyticus, a kind of bacterial pathogen that causes septicaemia. Hsp70 mRNA expression in gill, kidney, spleen, thymus gland, muscle and total-blood samples increased at first and then decreased gradually following heat shock. A similar time-dependent pattern was observed following V. alginolyticus pathogen challenge, in which Hsp70 mRNA expression peaked at 24 h after live bacterial infection and 3 days after dead bacterial vaccination. The results indicated that the Hsp70 gene was inducible and involved in the fish immune response.

Identification of a functional medaka heat shock promoter and characterization of its ability to induce exogenous gene expression in medaka in vitro and in vivo

Heat shock protein promoters (hsp promoters) are powerful tools for investigating gene functions, as the expression of targeted genes can be controlled simply by heating. However, there have been no reports of the utilization of an endogeneous medaka (Oryzias latipes) hsp promoter to induce exogenous gene expression in medaka. We identified and cloned a functional medaka hsp promoter (olphsp70.1) and verified its ability to act as an inducible promoter both in vitro and in vivo. The hsp promoter efficiently induced exogenous gene expression in cultured cells, developing embryos, and also in adult fishes. When used to control the expression of Venus, a variant of yellow fluorescent protein, in transgenic medaka, the hsp promoter was functional in all tissues except for the gonads of adults. These results indicate that the medaka hsp promoter can be a powerful tool for inducing exogenous gene expression and investigating gene functions both in vitro and in vivo in medaka.

Physiological adaptations of stressed fish to polluted environments: role of heat shock proteins

Fish are subjected to a wide variety of environmental stressors. Stressors affect fish at all life stages and the stress-specific responses that occur at the biochemical and physiological levels affect the overall health and longevity of such animals. In this review, the organ-specific alterations in fish that inhabit polluted environments are addressed in detail. Fish,like other vertebrates, have evolved strategies to counteract stress-mediated effects. Among the key strategies that fish have developed is the induction of HSPs. The primary functions of HSPs are to promote the proper folding or refolding of proteins, to prevent potentially damaging interactions with proteins, and aiding in the disassembly of formations of protein aggregates. Stress, a state of unbalanced tissue oxidation, causes a general disturbance in the cellular antioxidant and redox balance and evokes HSP70 overexpression. Distinct families of HSPs have diverse physiological functions, and their induction, which is regulated at the transcriptional level, is mediated by the activation of heat shock factors. Interestingly, HSPs also interact with a wide variety of signaling molecules that modulate stress-mediated apoptotic effects. Hence, HSP induction is of major importance for maintenance of cell homeostasis. HSP-mediated adaptation processes are regarded as a fundamental protective mechanism that decreases cellular sensitivity to damaging events. Thus, the adaptive expression of HSPs is a protective response that helps combat stress-induced conformational damage to proteins. Additional research is needed to gain further information on the functional significance and role of individual HSPs and to enhance the understanding of the molecular mechanisms by which they act. In addition, field studies are needed to allow comprehensive evaluation of the potential use of HSPs as biomarkers for environmental monitoring. Furthermore, the expression of HSPs in fish fluctuates in response to seasonal variation. Because HSPs serves as a tool for assessing the stressed state of individuals and/or populations, the impact of seasonal influences on constitutive and inducible factors of these proteins should also be elucidated. Such research will lead to a fundamental improvement in the understanding of the functional role of HSPs in response to natural environmental changes and may allow correlation of the action of HSPs at the molecular level with the whole organismal stress response, which, so far, remains unexplained.

Evaluation of the toxic impact of silver nanoparticles on Japanese medaka (Oryzias latipes)

The increased use of nano-sized metallic materials is likely to result in the release of these particles into the environment. It is, however, unclear if these materials are harmful to aquatic animals. Furthermore, because the dissolution of such nanomaterials will occur, it is probable that some of the adverse effects resulting will result from the dissolved metal species. In this study, therefore, we investigated the health and environmental impact of silver nanoparticles (Ag-NPs) on Japanese Medaka by studying changes in the expression of stress-related genes using real time RT-PCR analysis and compared these results with those of Medaka exposed to soluble silver ions. The stress-related genes selected here were metallothionein, HSP 70, GST, p53, CYP 1A and the transferrin gene. The expression levels of each gene were determined using two different Ag-NPs dosages and were quantified by measuring the mRNA concentrations in liver extracts with the Taqman-based Real-Time PCR method. The results suggest that these two silver forms have distinguishable toxic fingerprints between them. While the Ag-NPs led to cellular and DNA damage, as well as carcinogenic and oxidative stresses, genes related with metal detoxification/metabolism regulation and radical scavenging action were also induced. In contrast, the ionic silver led to an induction of inflammatory response and metallic detoxification processes in the liver of the exposed fish, but resulted in a lower overall stress response when compared with the Ag-NPs.

Genomic Cloning of a Heat Shock Cognate 71-1 Gene (HSC71-1) from the Hermaphroditic FishRivulus marmoratus(Cyprinodontiformes, Rivulidae)

The self-fertilizing fish Rivulus marmoratus (R. marmoratus) heat shock cognate 71 (HSC71) gene was cloned and characterized recently (Park et al., 2001). Here, we report the isolation of a homologue of the R. marmoratus HSC71 gene via screening of an R. marmoratus genomic DNA library. A 12,591 bp genomic fragment was sequenced and found to contain a 2844 bp open reading frame that consisted of 8 exons and showed high similarity to the previously reported R. marmoratus HSC71 gene. The two genes differed slightly at exons 5 and 8, and intron 3. On a deduced amino acid sequence level, the two R. marmoratus HSC71 genes were highly similar (89.3% in amino acid residues). In this paper, the author presented a homologous gene (R. marmoratus HSC71-1) similar to R. marmoratus HSC71 gene.

Identification of immune-related genes from kidney and spleen of turbot, Psetta maxima (L.), by suppression subtractive hybridization following challenge with Vibrio harveyi

Suppression subtractive hybridization was used to investigate the response of turbot, Psetta maxima (L.), to Vibrio harveyi, by using a cDNA library constructed from artificially infected turbot kidney and spleen mRNA. Forty-nine expressed sequence tags were obtained. Several immune system genes were identified, including a major histocompatibility complex (MHC) class Ia gene and a heat shock protein 70 gene. Some signalling molecules were also present in the cDNA libraries, including src-family tyrosine kinase SCK, sgk-1 serine-threonine protein kinase and amyloid precursor-like protein 2. The full length of MHC class Ia cDNA was cloned from turbot cDNA by rapid amplification of cDNA ends polymerase chain reaction. The nucleotide sequence of turbot MHC class Ia has been submitted to GenBank with accession number EF032639. The turbot MHC class Ia cDNA has an open reading frame encoding 354 amino acids, and the deduced amino acid sequence of turbot MHC class Ia has 68%, 54%, 51%, 52%, 57%, 33%, 29% and 29% identities to those of olive flounder, medaka, rainbow trout, Atlantic cod, tiger puffer, chicken, mouse and human, respectively. Quantitative reverse transcriptase-PCR was performed for the MHC class Ia gene, and it was revealed that the expression level of the MHC class Ia gene in V. harveyi-challenged turbot increased to fourfold that of the controls.

Arsenic-induced histopathology and synthesis of stress proteins in liver and kidney of Channa punctatus

As3+, considered effective for aquatic weed control, has been found to be harmful to several species of freshwater teleosts. Channa punctatus (Bloch) exposed for 14 days to nonlethal concentrations (1/20 LC50 and 1/10 LC50) of As2O3 were sampled on days 0, 1, 2, 7, and 14. Tissue disorientation, peliosis, and vacuolization accompanied by karyolysis, apoptosis, and necrosis of hepatocytes were significant on days 1, 2, and 7. In the kidney shrinkage of the glomerulus and increase in the Bowman's space were observed on days 1, 2, and 7. Irregularities in the renal tubule including apoptotic and necrotic cells were also common. Decreased intertubular space and enlargement of the height of the brush border cells were noteworthy. Corresponding with the histopathological lesions, dose-dependent disturbances in liver and renal functions and induction of heat shock protein 70 were significant at the early phase of arsenic treatment while metallothionein was induced at a later phase of treatment.

Are hsps suitable for indicating stressed states in fish?

In response to most stressors, fish will elicit a generalized physiological stress response, which involves the activation of the hypothalamic-pituitary-interrenal axis (HPI). As in other vertebrates, this generalized stress response comprises physiological responses that are common to a wide range of environmental, physical and biological stressors. Recently, several families of heat shock proteins (hsps) have been proposed as indicators of a generalized stress response at the cellular level. Recent findings that hsp levels, in various fish tissues, respond to a wide range of stressors have supported the use of these proteins as indicators of stressed states in fish. However, the cellular stress response can vary, for example, according to tissue, hsp family and type of stressor. This brief overview of these responses in fish asks the question of whether changes in levels and families of hsps can be used as a suitable indicator of stressed states in fish. By casting this question in the context of the well-established generalized physiological stress response in fish, we argue that the use of hsps as indicators of stressed states in fish in general is premature.

Identification and induction of hsp70 gene by heat shock and cadmium exposure in carp

A member of the multi-gene family, encoding 70 kD stress proteins, was identified from the common carp (Cyprimus carpio). Homologies, observed at both nucleic acid and amino acid levels, and also the intronless structure of this gene, strongly suggest that it corresponds to a heat-inducible hsp70 gene in carp. Gene-specific primers were selected and used in RT-PCR reactions to measure the basal hsp70 mRNA levels and to follow the inducer-specific expression of this gene in different tissues during in vivo studies. Carp hsp70 mRNA is not detectable in the brain and muscle, and its concentration is around the limit of detection in the kidney and liver of unstressed animals. The expression of hsp70 is induced by elevated temperature and it responds to Cd treatment in a tissue and time-dependent manner.

Heat shock protein genes and their functional significance in fish

Despite decades of intensive investigation, important questions remain regarding the functional, ecological, and evolutionary roles of heat shock proteins. In this paper, we discuss the utility of fish as a model system to address these questions, and review the relevant studies of heat shock protein genes and the regulation of their expression in fish. Although molecular studies of the heat shock proteins in fish are still in their early descriptive phase, data are rapidly being collected. More is known about the biotic and abiotic factors regulating heat shock proteins. We briefly review these studies and focus on the role of heat shock proteins in development, their regulation by the endocrine system, and their importance in fish in nature. Functional genomics approaches will provide the tools necessary to gain a comprehensive understanding of the significance of heat shock proteins in the cellular stress response, in the physiological processes at higher levels of organization, and in the whole animal in its natural environment.

Constitutive heat shock protein 70 (HSC70) expression in rainbow trout hepatocytes: effect of heat shock and heavy metal exposure

The 70-kDa family of heat shock proteins plays an important role as molecular chaperones in unstressed and stressed cells. The constitutive member of the 70 family (hsc70) is crucial for the chaperoning function of unstressed cells, whereas the inducible form (hsp70) is important for allowing cells to cope with acute stressor insult, especially those affecting the protein machinery. In fish, the role of hsc70 in the cellular stress response process is less clear primarily because of the lack of a fish-specific antibody for hsc70 detection. In this study, we purified hsc70 to homogeneity from trout liver using a three-step purification protocol with differential centrifugation, ATP-agarose affinity chromatography and electroelution. Polyclonal antibodies to trout hsc70 generated in rabbits cross-reacted strongly with both purified trout hsc70 protein and also purified recombinant bovine hsc70. Two-dimensional electrophoresis followed by Western blotting confirmed that the isoelectric point of rainbow trout hsc70 was more acidic than hsp70. Using this antibody, we detected hsc70 content in the liver, heart, gill and skeletal muscle of unstressed rainbow trout. Primary cultures of trout hepatocytes subjected to a heat shock (+15 degrees C for 1 h) or exposed to either CuSO(4) (200 microM for 24 h), CdCl(2) (10 microM for 24 h) or NaAsO(2) (50 microM for 1 h) resulted in higher hsp70 accumulation over a 24-h period. However, hsc70 content showed no change with either heat shock or heavy metal exposure suggesting that hsc70 is not modulated by sublethal acute stressors in trout hepatocytes. Taken together, we have for the first time generated polyclonal antibodies specific to rainbow trout hsc70 and this antibody will allow for the characterization of the role of hsc70 in the cellular stress response process in fish.

Heat shock stimulation of a tilapia heat shock protein 70 promoter is mediated by a distal element

We reported previously that a tilapia (Oreochromis mossambicus) heat shock protein 70 (HSP70) promoter is able to confer heat shock response on a reporter gene after transient expression both in cell culture and in microinjected zebrafish embryos. Here we present the first functional analysis of a fish HSP70 promoter, the tiHSP70 promoter. Using transient expression experiments in carp EPC (epithelioma papulosum cyprini) cells and in microinjected zebrafish embryos, we show that a distal heat shock response element (HSE1) at approx. -800 is predominantly responsible for the heat shock response of the tiHSP70 promoter. This element specifically binds an inducible transcription factor, most probably heat shock factor, and a constitutive factor. The constitutive complex is not observed with the non-functional, proximal HSE3 sequence, suggesting that both factors are required for the heat shock response mediated by HSE1.

Cloning and expression analysis of an inducible HSP70 gene from tilapia fish

We isolated and characterized the tilapia (Oreochromis mossambicus) HSP70 gene, highly homologous to other HSP70 genes. A dramatic increase of tilapia HSP70 mRNA levels was observed after heat shock of whole animals in all organs tested. Reporter constructs were tested for transient expression in carp cells and in microinjected zebrafish embryos. The entire isolated regulatory region (-851/+157) was able to mediate heat shock inducible expression of the reporter gene, with no preference for a particular tissue. Our studies represent the first transcriptional analysis of a HSP70 promoter from fish, revealing a powerful tool to direct controlled, tissue-independent gene expression in fish.

Heat shock genes and the heat shock response in zebrafish embryos

Heat shock genes exhibit complex patterns of spatial and temporal regulation during embryonic development in a wide range of organisms. Our laboratory has initiated an analysis of heat shock protein gene expression in the zebrafish, a model system that is now utilized extensively for the examination of early embryonic development of vertebrates. We have cloned members of the zebrafish hsp47, hsp70,\i and hsp90 gene families and shown them to be closely related to their counterparts in higher vertebrates. Whole mount in situ hybridization and Northern blot analyses have revealed that these genes are regulated in distinct spatial, temporal, and stress-specific manners. Furthermore, the tissue-specific expression patterns of the hsp47 and hsp90 alpha genes correlate closely with the expression of genes encoding known chaperone targets of Hsp47 and Hsp90 in other systems. The data raise a number of interesting questions regarding the function and regulation of these heat shock genes in zebrafish embryos during normal development and following exposure to environmental stress.