Molecular characterization of a heat shock cognate cDNA of zebrafish, hsc70, and developmental expression of the corresponding transcripts

Thermal stress induces heat shock protein 70 and apoptosis during embryo development in a Neotropical freshwater fish

Fish embryos are particularly vulnerable to temperature changes, with the effects varying with developmental stage. The major aim of the present study was to analyse the relationship between apoptosis and heat shock protein (HSP) 70 during embryo development under thermal stress conditions. To this end, Prochilodus lineatus embryos at the blastopore closure stage were subjected to one of three thermal treatments for 1h (Group 1, 25°C (control); Group 2, 20°C; Group 3, 30°C) and then examined at 0, 4 and 8h posttreatment (h.p.t.). The viability of embryos was highest in Group 1 (81.33±16.65%), followed by Group 3 and Group 2 (75.33±12.10% and 68.67±16.86% respectively), with significant difference between Groups 1 and 2 (P<0.05). At 0h.p.t., embryos subjected to thermal stress (Group 3) had a significantly higher number of terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling (TUNEL)- and caspase-3-labelled cells, and a lower number of HSP70-positive cells than those in the control group. At 4h.p.t., there was a decrease in the TUNEL reaction and an increase in HSP70 in embryos in Group 3. At 8h.p.t., the size of Group 3 embryos was significantly smaller than that of Group 1 embryos. The results indicate a cytoprotective role for HSP70, regulating caspase-3-mediated apoptosis during embryo development of P. lineatus; however, this mechanism is not effective in controlling embryo viability and larval malformations.

Physicochemical changes in liver and Hsc70 expression in pikeperch Sander lucioperca under heat stress

The pikeperch Sander lucioperca is an economically important freshwater species that is currently threatened by higher summer temperatures caused by global warming. To clarify the physiological state of pikeperch reared under relatively high temperatures and to acquire valuable biomarkers to monitor heat stress in this species, 100 fish were subjected to five different temperature treatments, ranging from 23 °C (control) to 36 °C. The physiological and biochemical indexes of liver and blood were determined, and heat-shock cognate 70 kDa protein (Hsc70) mRNA expression profiles were analyzed. The results showed that the activities of superoxide dismutase, catalase, and glutathione peroxidase in heat-stressed pikeperch first increased and then decreased, exhibiting peaks at 34 °C, 28 °C, and 28 °C, respectively. The level of thiobarbituric acid-reactive substances (TBARS) in all experimental groups was significantly higher than that of the control. The numbers of red blood cells, the packed-cell volume, and the contents of hemoglobin were significantly higher in the 34 °C and 36 °C treatment groups. Under heat stress, the albumin, cholesterol, and triglycerides contents decreased with increasing temperatures. Real-time fluorescence-based quantitative RT-PCR showed that Hsc70 mRNA levels increased in all eight of the tested tissues under heat stress. Expression reached maximum levels at 34 °C in the muscle, heart and gill tissues, and at 36 °C in the other five tissues. These results demonstrate that several physiological and biochemical phenotypes, such as oxidative stress, antioxidant enzymes and molecular chaperones, could be important biomarkers of heat stress in pikeperch, and are potentially valuable to uncover the mechanisms of heat-stress responses in fish.

White Shrimp Litopenaeus vannamei That Have Received Gracilaria tenuistipitata Extract Show Early Recovery of Immune Parameters after Ammonia Stressing

White shrimp Litopenaeus vannamei immersed in seawater (35‰) containing Gracilaria tenuistipitata extract (GTE) at 0 (control), 400, and 600 mg/L for 3 h were exposed to 5 mg/L ammonia-N (ammonia as nitrogen), and immune parameters including hyaline cells (HCs), granular cells (GCs, including semi-granular cells), total hemocyte count (THC), phenoloxidase (PO) activity, respiratory bursts (RBs), superoxide dismutase (SOD) activity, lysozyme activity, and hemolymph protein level were examined 24~120 h post-stress. The immune parameters of shrimp immersed in 600 mg/L GTE returned to original values earlier, at 96~120 h post-stress, whereas in control shrimp they did not. In another experiment, shrimp were immersed in seawater containing GTE at 0 and 600 mg/L for 3 h and examined for transcript levels of immune-related genes at 24 h post-stress. Transcript levels of lipopolysaccharide and β-1,3-glucan binding protein (LGBP), peroxinectin (PX), cytMnSOD, mtMnSOD, and HSP70 were up-regulated at 24 h post-stress in GTE receiving shrimp. We concluded that white shrimp immersed in seawater containing GTE exhibited a capability for maintaining homeostasis by regulating cellular and humoral immunity against ammonia stress as evidenced by up-regulated gene expression and earlier recovery of immune parameters.

Identification of a novel cognate cytosolic Hsp70 gene (MnHsc70-2) from oriental river prawn Macrobrachium nipponense and comparison of its expressions with the first cognate Hsc70 (MnHsc70-1) under different stresses

The 70-kDa family of heat-shock proteins (Hsp70) plays an important role in the host immunity, which is widely expressed in eukaryotic cells as a major chaperone protein. In the present study, the full-length complementary DNA (cDNA) of a second cognate cytosolic Hsp70 family member (MnHsc70-2) was cloned and characterized from Macrobrachium nipponense, which is an economically and nutritionally important crustacean. The cDNA was 2,717 bp, containing an open reading frame (ORF) of 1,950 bp, which encodes a protein of 649 amino acids with a theoretical molecular weight of 71.1 kDa and an isoelectric point of 5.27. Sequence alignment showed that the MnHsc70-2 shared 75-97 % identity with other heat-shock proteins. Compared to the previously identified cognate Hsp70 (MnHsc70-1) in M. nipponense, MnHsc70-2 showed quite different expression profiles under unstressed conditions in all tested tissues, including the hemocytes, heart, hepatopancreas, gill, intestine, nerve, and muscle. The phylogenetic analysis demonstrated that MnHsc70-2 showed the closest relationship with MnHsc70-1. Heat-inducibility assays showed that two isolated messenger RNAs (mRNAs) displayed different expression profiles in both the hepatopancreas and gill tissues. MnHsc70-1 mRNA expression level decreased at first and then increased to the normal level, whereas MnHsc70-2 mRNA level increased at first and then decreased. The expressions of two MnHsc70s showed substantial obvious heat-inducible regulation in both the hepatopancreas and gill. Under bacterial challenge by Aeromonas hydrophila, both MnHsc70-1 and MnHsc70-2 mRNA level was up-regulated moderately. The results suggested that two cognate Hsc70s may play essential functions in mediating responses to heat-shock and bacterial challenge.

Natural thermal adaptation increases heat shock protein levels and decreases oxidative stress

Heat shock proteins (HSPs), originally identified as heat-inducible gene products, are a family of highly conserved proteins that respond to a wide variety of stress including oxidative stress. Although both acute and chronic oxidative stress have been well demonstrated to induce HSP responses, little evidence is available whether increased HSP levels provide enhanced protection against oxidative stress under elevated yet sublethal temperatures. We studied relationships between oxidative stress and HSPs in a physiological model by using Garra rufa (doctor fish), a fish species naturally acclimatized to different thermal conditions. We compared fish naturally living in a hot spring with relatively high water temperature (34.4±0.6°C) to those living in normal river water temperature (25.4±4.7°C), and found that levels of all the studied HSPs (HSP70, HSP60, HSP90, HSC70 and GRP75) were higher in fish living in elevated water temperature compared with normal river water temperature. In contrast, indicators of oxidative stress, including protein carbonyls and lipid hydroperoxides, were decreased in fish living in the elevated temperature, indicating that HSP levels are inversely associated with oxidative stress. The present results provide evidence that physiologically increased HSP levels provide protection against oxidative stress and enhance cytoprotection.

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.

Convergent evolution of heat-inducibility during subfunctionalization of the Hsp70 gene family

BACKGROUND

Heat-shock proteins of the 70 kDa family (Hsp70s) are essential chaperones required for key cellular functions. In eukaryotes, four subfamilies can be distinguished according to their function and localisation in different cellular compartments: cytosol, endoplasmic reticulum, mitochondria and chloroplasts. Generally, multiple cytosol-type Hsp70s can be found in metazoans that show either constitutive expression and/or stress-inducibility, arguing for the evolution of different tasks and functions. Information about the hsp70 copy number and diversity in microbial eukaryotes is, however, scarce, and detailed knowledge about the differential gene expression in most protists is lacking. Therefore, we have characterised the Hsp70 gene family of Paramecium caudatum to gain insight into the evolution and differential heat stress response of the distinct family members in protists and to investigate the diversification of eukaryotic hsp70s focusing on the evolution of heat-inducibility.

RESULTS

Eleven putative hsp70 genes could be detected in P. caudatum comprising homologs of three major Hsp70-subfamilies. Phylogenetic analyses revealed five evolutionarily distinct Hsp70-groups, each with a closer relationship to orthologous sequences of Paramecium tetraurelia than to another P. caudatum Hsp70-group. These highly diverse, paralogous groups resulted from duplications preceding Paramecium speciation, underwent divergent evolution and were subject to purifying selection. Heat-shock treatments were performed to test for differential expression patterns among the five Hsp70-groups as well as for a functional conservation within Paramecium. These treatments induced exceptionally high mRNA up-regulations in one cytosolic group with a low basal expression, indicative for the major heat inducible hsp70s. All other groups showed comparatively high basal expression levels and moderate heat-inducibility, signifying constitutively expressed genes. Comparative EST analyses for P. tetraurelia hsp70s unveiled a corresponding expression pattern, which supports a functionally conserved evolution of the Hsp70 gene family in Paramecium.

CONCLUSIONS

Our analyses suggest an independent evolution of the heat-inducible cytosol-type hsp70s in Paramecium and in its close relative Tetrahymena, as well as within higher eukaryotes. This result indicates convergent evolution during hsp70 subfunctionalization and implies that heat-inducibility evolved several times during the course of eukaryotic evolution.

Identification of a heat shock cognate protein 70 gene in Chinese soft-shell turtle (Pelodiscus sinensis) and its expression profiles under thermal stress

The heat shock cognate protein 70 (Hsc70) is a member of a 70-kDa heat shock protein (HSP70) family that functions as molecular chaperones. In this study, a novel Hsc70 gene from Chinese soft-shelled turtle (Pelodiscus sinensis) (tHsc70) was identified. The tHsc70 full-length complementary DNA (cDNA) is 2272 bp long with a 1941-bp open reading frame (ORF) encoding 646 amino acids. Three characteristic signature regions of the HSP70 family, two major domains of an adenosine triphosphate (ATP)/guanosine triphosphate (GTP) binding domain (ABD), and a substrate-binding domain (SBD) were present in the predicted tHsc70 amino acid sequence. The tHsc70 gene was expressed in Escherichia coli BL21 and the expression product reacted with the anti-Hsc70 mouse monoclonal antibody by Western blotting. Homology analysis revealed that tHsc70 shared identity from 53.9% to 87.7% at the nucleotide level, and 49.1% to 99.5% at the amino acid level with the known Hsc70s. Phylogenetic analysis showed that tHsc70 was clustered together with the Hsc70 gene of another reptile species (Alligator mississippiensis). The tHsc70 was expressed in the liver, lung, heart, and skeletal muscle. The expression patterns of tHsc70 messenger RNA (mRNA) differed among different tissues under different durations of heat stress at 40 °C. Adaptation at 25 °C for 1 h after heat stress was also different among tissues and length of heat stress. Irrespective of different profiles of expression under heat stress, tHsc70 may play roles in protecting turtles from thermal stress.

Expression analysis of heat shock genes in the skin, spleen and blood of common carp (Cyprinus carpio) after cadmium exposure and hypothermia

Heat shock proteins are chaperones that play a pivotal role in controling multiple regulatory pathways such as stress defense, hormone signaling, cell cycle control, cell proliferation and differentiation, and apoptosis. In this study, the expression patterns of four well-known heat shock genes (hsp70, hsc70-1, hsc70-2 and hsp90α) were characterized in the skin, spleen and blood cells of the common carp, under unstressed conditions and after Cd2+ treatment or hypothermia. The examined genes were expressed in a tissue-specific manner: hsc70-2 was expressed constitutively, and was at best only slightly inducible; hsp90α exhibited a high basic expression in all three tissues, whereas hsc70-1 did so only in the blood cells, the expression of hsp70 proved to be below the level of detection in unstressed fish. Cold shock induced the expression of hsp genes in the spleen (hsp90α) and blood cells (hsp70, hsc70-1 and hsp90α), while Cd2+ treatment has no effect on the expression pattern. The highest inducibilities were detected in the skin: for hsp70 an induction of at least 20-fold after cadmium exposure, for hsc70-1 of at least 30-fold and for hsp90α of 3-fold after hypothermia.

Simple, economical heat-shock devices for zebrafish housing racks

One reason for the popularity of the zebrafish (Danio rerio) as a model vertebrate is the ability to manipulate gene expression in this organism. A common method is to induce gene expression transiently under control of a heat-shock promoter (e.g., hsp70l). By making simple mechanical adjustments to small aquarium heaters (25-50W), we were able to produce consistent and reliable heat-shock conditions within a conventional zebrafish housing system. Up to two heat-shock intervals per day (>37°C) could be maintained under conditions of continuous flow (5-25 mL/min). Temperature logging every 30 s indicated rapid warm up times, consistent heat-shock lengths, and accurate and precise peak water temperatures (mean±SD=38°C±0.2°C). The biological effects of these heat-shock treatments were confirmed by observing inducible expression of enhanced green fluorescent protein (EGFP) and inhibition of caudal fin regeneration in a transgenic fish line expressing a dominant negative fibroblast growth factor receptor (Tg(hsp70l:dnfgfr1-EGFP)(pd1)). These devices are inexpensive, easily modified, and can be calibrated to accommodate a variety of experimental designs. After setup on a programmable timer, the heaters require no intervention to produce consistent daily heat shocks, and all other standard care protocols can be followed in the fish facility. The simplicity and stability of these devices make them suitable for long-term heat shocks at any stage of the zebrafish lifecycle (>7 days postfertilization), and useful for both laboratory and classroom experiments on transgenic zebrafish.

Molecular cloning and characterization of gene encoding for cytoplasmic Hsc70 from Pennisetum glaucum may play a protective role against abiotic stresses

Molecular chaperones (Hsps) have been shown to facilitate protein folding or assembly under various developmental and adverse environmental conditions. The aim of this study was to unravel a possible role of heat-shock proteins in conferring abiotic stress tolerance to plants. We isolated a cDNA encoding a cytoplasmic Hsp70 (PgHsc70) from Pennisetum glaucum by screening heat-stress cDNA library. PgHsc70 cDNA encoding 649 amino acids represents all conserved signature motifs characteristic of Hsp70s. The predicted molecular model of PgHsc70 protein suggests that the N-terminus ATP-binding region is evolutionarily conserved, in comparison to C-terminus peptide-binding domains. A single intron in ATPase domain coding region of PgHsc70 exhibited a high degree of conservation with respect to its position and phasing among other plant Hsp70 genes. Recombinant PgHsc70 protein purified from E. coli possessed in vitro chaperone activity and protected PgHsc70 expressing bacteria from damage caused by heat and salinity stress. Nucleotide sequence analysis of 5' flanking promoter region of PgHsc70 gene revealed a potential heat-shock element (HSE) and other putative stress-responsive transcription factor binding sites. Positive correlation existed between differentially up-regulated PgHsc70 transcript levels and the duration and intensity of different environmental stresses. Molecular and biochemical analyses revealed that PgHsc70 gene was a member of the Hsp70 family and suggested that its origin was from duplication of a common ancestral gene. Transcript induction data, presence of several putative stress-responsive transcription factor-binding sites in the promoter region of PgHsc70 and the presence of a protective in vitro chaperone activity of this protein against damage caused by heat and salinity, when expressed in E. coli, suggest its probable role in conferring abiotic stress tolerance to this plant.

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.

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.

Expression analysis of selected immune-relevant genes in channel catfish during Edwardsiella ictaluri infection

Channel catfish Ictalurus punctatus were intraperitoneally challenged with the bacterium Edwardsiella ictaluri (the causative agent of enteric septicemia of catfish), and the expression of genes presumed to function in the inducible innate defense was evaluated. End-binding protein 1 (EB1), beta1-integrin, natural-resistance-associated macrophage protein (Nramp), heat shock protein 70 (Hsp70), serum amyloid P (SAP), and transferrin gene expression profiles were determined using quantitative reverse-transcriptase-polymerase chain reaction on liver, anterior kidney, spleen, and gut. Fish were subsampled at 0, 24, 48, 72, and 96 h after bacterial or phosphate-buffered-saline injection. Posterior kidney sampling demonstrated increasing bacterial counts at 24-48 h postinjection (hpi), followed by a plateau to 96 hpi. The transferrin and SAP transcripts were liver specific. The other genes were expressed in all four tissues. In bacterially infected fish, expression of EB1 (anterior kidney, spleen, and liver), Hsp70 (anterior kidney and spleen), and Nramp (spleen and gut) significantly increased by 48 hpi. Transferrin was strongly up-regulated and SAP was downregulated by 72 hpi, indicating positive and negative acute-phase reactants, respectively. The data indicate a substantial response of innate immunity effector cells by 48 hpi, followed by suppression of bacterial growth and induction of the acute-phase response. This suggests that the 48-72-hpi time frame is critical in our model for evaluating the effectiveness of innate defenses.

Identification and characterization of zebrafish ocular formation genes

To study genes that are specifically expressed in the eyes, we employed microarray and in situ hybridization analyses to identify and characterize differentially expressed ocular genes in eyeless masterblind (mbl-/-) zebrafish (Danio rerio). Among 70 differentially expressed genes in the mbl-/- mutant identified by microarray analysis, 8 down-regulated genes were characterized, including 4 eye-specific genes, opsin 1 short-wave-sensitive 1 (opn1sw1), crystallinbetaa1b (cryba1b), crystallinbetaa2b (cryba2b), and crystallingamma M2d3 (crygm2d3); 2 eye and brain genes, ATPase, H+ transporting, lysosomal, V0 subunit c (atp6v0c) and basic leucine zipper and W2 domains 1a (bzw1a); and 2 constitutive genes, heat shock protein 8 (hspa8) and ribosomal protein L7a (rpl7a). In situ hybridization experiments confirmed down-regulation of these 8 ocular formation genes in mbl-/- zebrafish and showed their ocular and dynamic temporal expression patterns during zebrafish early development. Further, an automated literature analysis of the 70 differentially expressed genes identified a sub-network of genes with known associations, either with each other or with ocular structures or development, and shows how this study contributes to the current body of knowledge.

Comparative genome analysis of the neurexin gene family in Danio rerio: insights into their functions and evolution

Neurexins constitute a family of proteins originally identified as synaptic transmembrane receptors for a spider venom toxin. In mammals, the 3 known Neurexin genes present 2 alternative promoters that drive the synthesis of a long (alpha) and a short (beta) form and contain different sites of alternative splicing (AS) that can give rise to thousands of different transcripts. To date, very little is known about the significance of this variability, except for the modulation of binding to some of the Neurexin ligands. Although orthologs of Neurexins have been isolated in invertebrates, these genes have been studied mostly in mammals. With the aim of investigating their functions in lower vertebrates, we chose Danio rerio as a model because of its increasing importance in comparative biology. We have isolated 6 zebrafish homologous genes, which are highly conserved at the structural level and display a similar regulation of AS, despite about 450 Myr separating the human and zebrafish species. Our data indicate a strong selective pressure at the exonic level and on the intronic borders, in particular on the regulative intronic sequences that flank the exons subject to AS. Such a selective pressure could help conserve the regulation and consequently the function of these genes along the vertebrates evolutive tree. AS analysis during development shows that all genes are expressed and finely regulated since the earliest stages of development, but mark an increase after the 24-h stage that corresponds to the beginning of synaptogenesis. Moreover, we found that specific isoforms of a zebrafish Neurexin gene (nrxn1a) are expressed in the adult testis and in the earliest stages of development, before the beginning of zygotic transcription, indicating a potential delivery of paternal RNA to the embryo. Our analysis suggests the existence of possible new functions for Neurexins, serving as the basis for novel approaches to the functional studies of this complex neuronal protein family and more in general to the understanding of the AS mechanism in low vertebrates.

Heat shock factor 1 is required for constitutive Hsp70 expression and normal lens development in embryonic zebrafish

Heat shock factors (HSFs) are the major transcription factors responsible for heat-induced upregulation of heat shock protein (Hsp) genes. All three mammalian HSFs (HSF1, HSF2, HSF4) have also been shown to be required for normal mammalian development. It is currently unknown if HSFs play similarly important roles during normal development of non-mammalian vertebrates. In the present study, a morpholino modified antisense oligonucleotide (MO) approach targeted against hsf1 mRNA (hsf1-MO) was used to examine the requirement of HSF1 in zebrafish development. Embryos depleted of HSF1 displayed a reproducible small eye phenotype characterized by an immature lens and a disorganized retinal structure. These defects were strikingly similar to those observed when constitutive, lens specific Hsp70 expression was reduced through the microinjection of MO targeting hsp70. The data suggest that HSF1 is involved in regulating constitutive lens specific expression of hsp70 in the embryonic zebrafish. This conclusion is supported by a marked reduction in Hsp70 protein in hsf1-MO injected embryos. Microinjection of MO targeted to hsf2 mRNA (hsf2-MO) did not result in a small eye phenotype in a significant number of embryos. These data also suggest that HSF1 and HSF2 play distinct roles in non-mammalian vertebrates, similarly to what has been demonstrated previously in mouse.

Proteome analysis identifies novel protein candidates involved in regeneration of the cerebellum of teleost fish

In contrast to mammals, adult teleost fish exhibit an enormous potential to regenerate neuronal tissue after injuries to the CNS. By combining a well-defined cerebellar lesion paradigm with differential proteome analysis at a post-lesion survival time of 3 days, we screened for protein candidates involved in repair of the fish brain. Out of nearly 900 protein spots detected on 2-D gels, spot intensity was significantly increased at least twofold in 30 spots and decreased to at least half the intensity of control tissue in 23 spots. The proteins associated with 24 of the spots were identified by PMF and MS/MS fragmentation. The cellular localization and the spatiotemporal patterns of two of these proteins, beta-actin and beta-tubulin, were further characterized through immunohistochemistry. Comparison of the observed changes in protein abundance with the previously characterized events underlying regeneration of the cerebellum suggests that the proteins identified are especially involved in cellular proliferation and survival, as well as axonal sprouting.

Molecular cloning and expression of two HSP70 genes in the prawn, Macrobrachium rosenbergii

Two complementary deoxyribonucleic acid (cDNA) clones encoding 2 different 70-kDa heat shock proteins (HSPs) were isolated from the prawn Macrobrachium rosenbergii. The cDNA clones were 2448 and 2173 bp in length and contained 1950- and 1734-bp open reading frames (ORFs), respectively. The ORFs encoded 649- and 577-amino acid polypeptides, which were named Mar-HSC70 and Mar-HSP70, respectively, according to the sequence identities with other known HSC70s and HSP70s and based on their inducibility in response to heat shock stress (at 35 degrees C). Genomic DNA sequence analysis revealed no introns in either gene. The major structural differences between the 2 proteins were a 60-amino acid segment and a 14-amino acid segment present in the N-terminal and C-terminal, respectively, of Mar-HSC70 that were not found in Mar-HSP70. Northern blotting and semiquantitative reverse transcription-polymerase chain reaction analyses indicated that the Mar-HSP70 gene was expressed under heat shock (35 degrees C) stress in a non-tissue-specific manner. In contrast, Mar-HSC70 messenger ribonucleic acid was constitutively expressed in every tissue except muscle, and its expression in response to heat shock (at 35 degrees C) changed only in muscle.

Cloning and molecular characterization of heat shock cognate 70 from tiger shrimp (Penaeus monodon)

We cloned the complementary deoxyribonucleic acid (cDNA) of the heat shock cognate 70 (hsc70) gene of tiger shrimp (Penaeus monodon). It was 2207 bp long and included a 1959-bp coding region, a 40-bp flanking region at the 5' end, and a 208-bp flanking region at the 3' end. The deduced, 652-amino acid sequence had a molecular mass of 71 481 Da and an estimated isoelectric point (pI) of 5.2. Based on phylogenetic analysis, the gene is clustered with the hsc70 proteins of invertebrates and vertebrates. In native gel electrophoresis, recombinant P. monodon hsc70 expressed in an Escherichia coli system is tightly associated with carboxymethylated alpha-lactalbumin (CMLA), which indicates that hsc70 probably functions as a chaperone. In an in vitro adenosine triphosphatase assay, recombinant hsc70 hydrolyzed adenosine triphosphate to adenosine-5'-diphosphate and increased hydrolysis activity by binding to unfolded peptide, CMLA. In situ hybridization using an antisense riboprobe revealed that the hsc70 gene was active in most tissues of unstressed shrimp. The expression of hsc70 messenger ribonucleic acid (mRNA) in hemocytes increased 2- to 3-fold at the first hour after shrimp experienced heat shock and 0.5-hour recovery. Hsc70 mRNA decreased gradually to the background level. Cloning and characterizing the P. monodon hsc70 gene is the first, crucial step in studying the relationship of heat shock proteins with the stress or immune responses of shrimp.

Zebrafish Hsp70 is required for embryonic lens formation

Heat shock proteins (Hsps) were originally identified as proteins expressed after exposure of cells to environmental stress. Several Hsps were subsequently shown to play roles as molecular chaperones in normal intracellular protein folding and targeting events and to be expressed during discrete periods in the development of several embryonic tissues. However, only recently have studies begun to address the specific developmental consequences of inhibiting Hsp expression to determine whether these molecular chaperones are required for specific developmental events. We have previously shown that the heat-inducible zebrafish hsp70 gene is expressed during a distinct temporal window of embryonic lens formation at normal growth temperatures. In addition, a 1.5-kb fragment of the zebrafish hsp70 gene promoter is sufficient to direct expression of a gfp reporter gene to the lens, suggesting that the hsp70 gene is expressed as part of the normal lens development program. Here, we used microinjection of morpholino-modified antisense oligonucleotides (MOs) to reduce Hsp70 levels during zebrafish development and to show that Hsp70 is required for normal lens formation. Hsp70-MO-injected embryos exhibited a small-eye phenotype relative to wild-type and control-injected animals, with the phenotype discernable during the second day of development. Histological and immunological analysis revealed a small, underdeveloped lens. Numerous terminal deoxynucleotidyl transferase-mediated dUTP-fluoroscein nick-end labeling (TUNEL)-positive nuclei appeared in the lens of small-eye embryos after 48 hours postfertilization (hpf), whereas they were no longer apparent in untreated embryos by this age. Lenses transplanted from hsp70-MO-injected embryos into wild-type hosts failed to recover and retained the immature morphology characteristic of the small-eye phenotype, indicating that the lens phenotype is lens autonomous. Our data suggest that the lens defect in hsp70-MO-injected embryos is predominantly at the level of postmitotic lens fiber differentiation, a result supported by the appearance of mature lens organization in these embryos by 5 days postfertilization, once morpholino degradation or dilution has occurred.

Heat shock gene expression and function during zebrafish embryogenesis

Recent work in the zebrafish, Danio rerio, indicates that heat shock genes are expressed in unique spatial patterns under non-stress conditions. In particular, hsp90alpha is expressed during the normal differentiation of striated muscle fibres, and hsp70-4 is expressed during normal lens development in the eye. Furthermore, disruption of the activity of either of these genes or their protein products gives rise to unique embryonic phenotypes that result from failures in proper somitic muscle development and lens development, respectively. Embryonic hsp70-4 expression is also activated in a cell-specific manner following heavy metal exposure. This has allowed for the development of a hsp70-4/eGFP reporter gene system in stable transgenic zebrafish that serves as a reliable yet extremely quick indicator of cell-specific toxicity in the context of the multicellular, living embryo.

The use of mature zebrafish (Danio rerio) as a model for human aging and disease

Zebrafish (Danio rerio) have been extensively utilized for understanding mechanisms of development. These studies have led to a wealth of resources including genetic tools, informational databases, and husbandry methods. In spite of all these resources, zebrafish have been underutilized for exploring pathophysiology of disease and the aging process. Zebrafish offer several advantages over mammalian models for these studies, including the ability to perform saturation mutagenesis and the capability to contain thousands of animals in a small space. In this review, we will discuss the use of mature zebrafish as an animal model and provide specific examples to support this novel use of zebrafish. Examples include demonstrating that clinical pathology can be performed in mature zebrafish and that age-associated changes in heat shock response can be observed in zebrafish. These highlights demonstrate the utility of zebrafish as a model for disease and aging.

Constitutive roles for inducible genes: evidence for the alteration in expression of the inducible hsp70 gene in Antarctic notothenioid fishes

Previous research on the Antarctic notothenioid fish Trematomus bernacchii demonstrated the loss of the heat shock response (HSR), a classical cellular defense mechanism against thermal stress, characterized by the rapid synthesis of heat shock proteins (Hsps). In the current study, we examined potential mechanisms for the apparent loss of the HSR in Antarctic notothenioids and, in addition, compared expression patterns of two genes from the 70-kDa Hsp family (hsc71 and hsp70) in tissues from T. bernacchii to expression patterns in tissues of two closely related temperate notothenioid fishes from New Zealand, Bovichtus variegatus and Notothenia angustata. The results showed that transcript for both the constitutive and inducible genes in the Hsp70 gene family were expressed in detectable levels in all three species. However, only the cold-temperate New Zealand fishes displayed the ability to upregulate the inducible transcript, hsp70. Although hsp70 was present in detectable levels in several tissues of the Antarctic notothen T. bernacchii, in vitro thermal stresses failed to produce a significant increase in mRNA levels. In all species, the expression of the constitutive transcript hsc71 was variable and nonresponsive to temperature increases, even at temperatures as high as 10 degrees C above the ecologically relevant range for the species under study. Field-collected tissues from T. bernacchii (sampled immediately after capture) indicated that hsp70 mRNA was expressed at high levels in field-acclimatized fishes. Thus upregulation of molecular chaperones suggested that low-temperature stress may be significantly denaturing to cellular proteins in Antarctic fish, an observation that was supported by elevated levels of ubiquitin-conjugated protein.

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.

Heat- and cold-inducible regulation of HSP70 expression in zebrafish ZF4 cells

Elevated temperature induces a rapid heat shock transcription factor (HSFs)-mediated expression of heat shock (hsp) genes. The effect of cold exposure on hsp gene expression has hardly been investigated, although ectothermic animals experience both cold and heat stress. We have previously shown in zebrafish that the expression of hsf1a and a unique isoform hsf1b vary in a tissue-specific manner upon heat stress. In the current study, using a zebrafish (Danio rerio) embryonic cell line (ZF4), we have compared the effects of heat shock (28-->37 degrees C) vs. cold shock (28-->20 degrees C) on the expression of ahsf1a, zhsf1b and hsp70. Concomitantly, the suitability of the ZF4 cells as a model system was verified. The expression pattern of HSP70 proteins following heat or cold exposure is distinct, and the total HSP70 level is upregulated or stable, respectively. Moreover, heat exposure specifically increases the ratio of zhsf1a/b expression (10-fold), whereas cold exposure decreases it to one half. These data suggest that the zhsf1a/zhsf1b ratio is regulated in a temperature-dependent manner, and the ratio may be indicative of the stressor-specific HSP70 expression. Furthermore, the response in ZF4 cells upon heat shock resembles the response observed in zebrafish liver and thus, supports the use of this cell line in stress response studies.

Tissue- and stressor-specific differential expression of two hsc70 genes in carp

Two genes expressing 70 kDa heat shock proteins were identified in Cyprinus carpio. The sequence similarities and the intron-interrupted structure of the coding regions indicate that carp Hsc70-1 and Hsc70-2 belong to the Hsp70 cognate subfamily. The expressions of the two hsc70 genes were followed by semi-quantitative RT-PCR. Both genes are expressed under unstressed conditions in a characteristic tissue-specific manner. Inducibility of the response to elevated temperature, cold shock, and Cd treatment was investigated in the liver and muscle, in whole-animal experiments. Both genes were insensitive to or only weakly induced by the stressors, with two exceptions: Cd treatment resulted in an 11-13-fold enhanced induction of hsc70-1 in the liver and cold shock enhanced induction of hsc70-2 in the muscle by 7.5-10-fold.

Differential regulation of spontaneous and heat-induced HSP 70 expression in developing zebrafish (Danio rerio)

A spontaneous high expression of heat shock protein 70 (HSP 70) was found to arise in zebrafish (Danio rerio) at the larval stage (84 hr after fertilization). The level of HSP 70 in 84-hr-old larvae was estimated to be six- to eightfold that of 12-hr-old embryos. As heat-induced HSP 70 synthesis in many eukaryotic organisms is known to be mediated by a transcriptional-dependent pathway activated by heat shock factor 1 (HSF-1), we then examined if the spontaneous and heat-induced HSP 70 synthesis in zebrafish were controlled by the same mechanism. Although the transient increase of a 62-kDa HSF-1-like polypeptide in 72- to 96-hr-old larvae seemed to correlate with the onset of the spontaneous HSP 70 production, an anti-HSF-1 antibody cocktail supershifted the heat shock element (HSE) binding complex induced by stressed but not by unstressed zebrafish extracts. Northern blot and quantitative RT-PCR analysis demonstrated the predominant presence of the cognate form of hsp 70 mRNA (hsc 70 mRNA) in developing zebrafish. The extent of heat-induced HSP 70 production in 84-hr-old larvae matched well with a dramatic increase in hsp 70 mRNA accumulation, while no apparent increase in total hsp 70 mRNA could be detected in 72- to 84-hr-old unstressed larvae by northern blot analysis. The stable expression of hsc 70 mRNA specific to beta-actin mRNA in normal zebrafish was confirmed by RT-PCR analysis. Hence, the spontaneous high expression of HSP 70 in zebrafish is believed to be controlled by a mechanism different from the HSF-1-dependent transcriptional activation of hsp 70 under heat stress. J. Exp. Zool. 293:349-359, 2002.

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.

Genomic cloning of the Hsc71 gene in the hermaphroditic teleost Rivulus marmoratus and analysis of its expression in skeletal muscle: identification of a novel muscle-preferred regulatory element

To further our understanding of the role of stress proteins in development as well as in adaptation of fish to adverse environmental conditions, we undertook molecular analyses of stress protein encoding genes from the hermaphroditic teleost Rivulus marmoratus. We isolated a genomic clone containing the Hsc71 gene (rm-hsc71m) and its upstream sequences. rm-Hsc71m is not induced by external stress, but is enriched in a tissue-specific manner during early development. In adult, the strongest expression appeared in skeletal muscle, whereas lower expression was seen in the gill, eye and brain. To understand the regulatory basis of high muscle expression of rm-hsc71m, transfection of R.marmoratus muscle tissue was performed using 5' deletion fragments containing the rm-hsc71m promoter driving EGFP expression. An upstream region from -2.7 to -1.9 kb was identified as a muscle-specific regulatory region. Within this region, we identified at least three sites with the novel sequence TGTnACA interacting with a fish muscle factor having an M(r) of 32 000. Our data indicate that rm-hsc71m expression in skeletal muscle is controlled by a muscle-specific regulatory element containing this novel motif.

Zebrafish Hsp40 and Hsc70 genes are both induced during caudal fin regeneration

We report the characterization of a zebrafish DnaJ-like protein, homologue to the human Hsp40 protein hdj1, that we named zf-Hsp40. We have studied its expression during fin regeneration and we show that zf-Hsp40 mRNA level is drastically increased in all ray segments beneath the regenerated part, or blastema, in response to caudal fin amputation. In order to investigate whether zf-Hsp40 is part of a stress response system after injury, we studied the expression of the zebrafish Hsc70 transcript. Our results show a correlation between the expression of the two transcripts.

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.

Stress-induced, tissue-specific enrichment of hsp70 mRNA accumulation in Xenopus laevis embryos

In this study, we have employed whole-mount, in situ hybridization to study the spatial pattern of hsc70 and hsp70 mRNA accumulation in normal and heat shocked embryos during Xenopus laevis development. Our findings revealed that hsc70 mRNA was constitutively present in a global fashion throughout the embryo and was not heat inducible. Accumulation of hsp70 mRNA, however, was detected only in heat shocked embryos. Furthermore, hsp70 mRNA accumulation was enriched in a tissue-specific manner in X. laevis tailbud embryos within 15 minutes of a 33 degrees C heat shock. Abundant levels of heat shock-induced hsp70 mRNA were detected in the head region, including the lens placode, the cement gland, and in the somitic region and proctodeum. Preferential heat-induced accumulation of hsp70 mRNA was first detected at a heat shock temperature of 30 degrees C. Placement of embryos at 22 degrees C after a 1-hour, 33 degrees C heat shock resulted in decreased hsp70 mRNA with time, but the message persisted in selected tissues, including the lens placode and somites. Treatment of tailbud embryos with either sodium arsenite or zinc chloride induced a tissue-specific enrichment of hsp70 mRNA in the lens placode and somitic region. These studies reveal the complex nature of the heat shock response in different embryonic tissues and suggest the presence of regulatory mechanisms that lead to a stressor-induced, tissue-specific enrichment of hsp70 mRNA.

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.