HSP 90 alpha and HSP 90 beta genes are present in the zebrafish and are differentially regulated in developing embryos

Heat stress-induced heat shock protein 70 expression is dependent on ERK activation in zebrafish (Danio rerio) cells

Heat shock response is a common event that occurs in many species. Despite its evolutionary conservation, comparative studies of heat shock response have been largely unexplored. In mammals, heat shock response decreases with age through unclear mechanisms. Understanding how the age-related decline in heat shock response occurs may provide information to understanding the biology of aging. We have previously shown that heat shock response similarly declines with age in zebrafish. However, signaling pathways that regulate the heat shock response in zebrafish are unknown. In mammals there is evidence that mitogen-activated protein kinases (MAPKs) of the ERK family alter Hsp70 transcription, serving as a potential regulator of the heat shock response. We explored if heat stress-induced Hsp70 expression is altered by activation of ERK in the zebrafish Pac2 fibroblast cell line as occurs in mammalian cells. Heat stress induced both Hsp70 mRNA expression and phosphorylation of both ERK1 and ERK2 (ERK1/2) in Pac2 cells. ERK inhibitors PD98059 and U0126 blocked both heat stress-induced and plated-derived growth factor (PDGF)-induced ERK1/2 phosphorylation, and also diminished heat-induced Hsp70 expression. Pac2 cell viability was not affected by either the ERK inhibitors or heat stress. These results demonstrate that induction of Hsp70 in response to heat stress is dependent on ERK activation in Pac2 cells. This suggests that the heat shock response in zebrafish utilizes a similar signaling pathway to that of mammals and that zebrafish are a good model for comparative studies of heat shock response.

Shuttling of the chaperones Unc45b and Hsp90a between the A band and the Z line of the myofibril

The formation of thick filaments in striated muscle involves the chaperones Hsp90a and Unc45. We show that Unc45b and Hsp90a, two zebrafish orthologues, colocalize with myosin during myofibrillogenesis and associate with the Z line when myofibril assembly is completed. In response to stress or damage to the myofiber, Unc45b and Hsp90a dissociate from the Z line and transiently associate with myosin. Although chaperone activity of Unc45b requires the full-length protein, only the central and Unc45-Cro1p-She4p domains are required to anchor it to the Z line, and multiple subdomains mediate association with nascent myosin. We propose that the Z line serves as a reservoir for chaperones, allowing a rapid mobilization in response to muscle damage. Our data are consistent with a differential affinity model as an explanation for the shuttling of the chaperones between the Z line and myosin.

Development of a heat shock inducible gfp transgenic zebrafish line by using the zebrafish hsp27 promoter

In the present study, a zebrafish hsp27 promoter was isolated and used to develop heat shock inducible gfp transgenic zebrafish. The endogenous hsp27 mRNAs were constitutively expressed from 4 hpf and increased in several regions of brain, heart and somites in early embryogenesis until 24 hpf. Subsequently, the expression was reduced significantly but maintained in the heart and ears. Heat shock induced hsp27 mRNAs in the blastoderm from 6 hpf and later in somites, branchial arches and several regions of brain. Similarly in hsp27-gfp transgenic zebrafish, constitutive GFP expression was observed from 11 hpf. GFP expression was mainly in the skin cells and increased to the peak level at 7 dpf, followed by a reduction. The constitutive GFP expression in the heart was initiated from 50 hpf and maintained even in the adult fish. After heat shock, GFP expression was mainly induced in the muscle in addition to a mild increase in the skin and heart. The early stages of the embryos were more sensitive than late stages as the time required for induced GFP expression in the muscle is shorter. Thus, the hsp27-gfp transgenic line generally recapitulates the expression pattern and heat shock inducibility of endogenous hsp27 RNAs. We also tested the potential of using the hsp27-gfp transgenic zebrafish embryos for heavy metal induction and demonstrated the inducibility of GFP expression by arsenic; this pattern of induction was also supported by examination of endogenous hsp27 mRNA.

Environmental and genetic modifiers of squint penetrance during zebrafish embryogenesis

The Nodal-related subgroup of the TGFbeta superfamily of secreted cytokines regulates the specification of the mesodermal and endodermal germ layers during gastrulation. Two Nodal-related proteins - Squint (Sqt) and Cyclops (Cyc) - are expressed during germ-layer specification in zebrafish. Genetic sqt mutant phenotypes have defined a variable requirement for zygotic Sqt, but not for maternal Sqt, in midline mesendoderm development. However a comparison of phenotypes arising from oocytes or zygotes injected with Sqt antisense morpholinos has suggested a novel requirement for maternal Sqt in dorsal specification. In this study we examined maternal-zygotic mutants for each of two sqt alleles and we also compared phenotypes of closely related zygotic and maternal-zygotic sqt mutants. Each of these approaches indicated there is no general requirement for maternal Sqt. To better understand the dispensability of maternal and zygotic Sqt, we sought out developmental contexts that more rigorously demand intact Sqt signalling. We found that sqt penetrance is influenced by genetic modifiers, by environmental temperature, by levels of residual Activin-like activity and by Heat-Shock Protein 90 (HSP90) activity. Therefore, Sqt may confer an evolutionary advantage by protecting early-stage embryos against detrimental interacting alleles and environmental challenges.

HSP90β is involved in signaling prolactin-induced apoptosis in newt testis

We have shown in vivo and in vitro that prolactin induces apoptosis in the 7th generation of spermatogonia during newt spermatogenesis, but the underlying molecular mechanism remained unknown. To determine the role of heat shock protein (HSP) 90beta, a molecular chaperone for client proteins in signal transduction and transcriptional regulation, in prolactin-induced apoptosis, we cloned HSP90beta cDNA from newt testis. HSP90beta was detected highly at spermatogonial stage and in both the membrane and cytosol fractions only in germ cell-enriched fraction, while prolactin receptor was expressed in the membrane fraction of only germ cells. Co-immunoprecipitation demonstrated that HSP90beta associated constitutively with prolactin receptor on the plasma membrane of germ cells, suggesting that prolactin receptor is also one of the client proteins for HSP90beta. Inhibition of HSP90beta function by geldanamycin was shown to promote spermatogonial apoptosis. Taken together, these results suggest that HSP90beta is involved in signaling prolactin-induced apoptosis through the receptor.

Proteomic analysis of protein profiles during early development of the zebrafish, Danio rerio

In the present study, profiles of protein expression were examined during early development of zebrafish, an increasingly popular experimental model in vertebrate development and human diseases. By 2-DE, an initial increase in protein spots from 6 h post-fertilization (hpf) to 8-10 hpf was observed. There was no dramatic change in protein profiles up to 18 hpf, but significant changes occurred in subsequent stages. Interestingly, 49% of the proteins detected at 6 hpf remained detectable by 1 week of age. To map the protein expression patterns in 2-D gels, MALDI-TOF/TOF MS was employed to identify selected protein spots from early embryos. 108 protein spots were found to match known proteins and they were derived from 55 distinct genes. Interestingly, 11 (20%) of them produced multiple protein isoforms or distinct cleavage products. Although deyolked embryos were used in the analysis, a large number of vitellogenin derivatives remained prominently present in the embryos. Other than these, most of the identified proteins are cytosolic, cytoskeletal and nuclear proteins, which are involved in diversified functions such as metabolism, cytoskeleton, translation, protein degradation, etc. Some of the proteins with interesting temporal expression profiles during development are further discussed.

Comparative genomics and evolution of the HSP90 family of genes across all kingdoms of organisms

BACKGROUND

HSP90 proteins are essential molecular chaperones involved in signal transduction, cell cycle control, stress management, and folding, degradation, and transport of proteins. HSP90 proteins have been found in a variety of organisms suggesting that they are ancient and conserved. In this study we investigate the nuclear genomes of 32 species across all kingdoms of organisms, and all sequences available in GenBank, and address the diversity, evolution, gene structure, conservation and nomenclature of the HSP90 family of genes across all organisms.

RESULTS

Twelve new genes and a new type HSP90C2 were identified. The chromosomal location, exon splicing, and prediction of whether they are functional copies were documented, as well as the amino acid length and molecular mass of their polypeptides. The conserved regions across all protein sequences, and signature sequences in each subfamily were determined, and a standardized nomenclature system for this gene family is presented. The proeukaryote HSP90 homologue, HTPG, exists in most Bacteria species but not in Archaea, and it evolved into three lineages (Groups A, B and C) via two gene duplication events. None of the organellar-localized HSP90s were derived from endosymbionts of early eukaryotes. Mitochondrial TRAP and endoplasmic reticulum HSP90B separately originated from the ancestors of HTPG Group A in Firmicutes-like organisms very early in the formation of the eukaryotic cell. TRAP is monophyletic and present in all Animalia and some Protista species, while HSP90B is paraphyletic and present in all eukaryotes with the exception of some Fungi species, which appear to have lost it. Both HSP90C (chloroplast HSP90C1 and location-undetermined SP90C2) and cytosolic HSP90A are monophyletic, and originated from HSP90B by independent gene duplications. HSP90C exists only in Plantae, and was duplicated into HSP90C1 and HSP90C2 isoforms in higher plants. HSP90A occurs across all eukaryotes, and duplicated into HSP90AA and HSP90AB in vertebrates. Diplomonadida was identified as the most basal organism in the eukaryote lineage.

CONCLUSION

The present study presents the first comparative genomic study and evolutionary analysis of the HSP90 family of genes across all kingdoms of organisms. HSP90 family members underwent multiple duplications and also subsequent losses during their evolution. This study established an overall framework of information for the family of genes, which may facilitate and stimulate the study of this gene family across all organisms.

The HSP90 family of genes in the human genome: insights into their divergence and evolution

HSP90 proteins are important molecular chaperones. Transcriptome and genome analyses revealed that the human HSP90 family includes 17 genes that fall into four classes. A standardized nomenclature for each of these genes is presented here. Classes HSP90AA, HSP90AB, HSP90B, and TRAP contain 7, 6, 3, and 1 genes, respectively. HSP90AA genes mapped onto chromosomes 1, 3, 4, and 11; HSP90AB genes mapped onto 3, 4, 6, 13 and 15; HSP90B genes mapped onto 1, 12, and 15; and the TRAP1 gene mapped onto 16. Six genes, HSP90AA1, HSP90AA2, HSP90N, HSP90AB1, HSP90B1 and TRAP1, were recognized as functional, and the remaining 11 genes were considered putative pseudogenes. Amino acid polymorphic variants were detected for genes HSP90AA1, HSP90AA2, HSP90AB1, HSP90B1, and TRAP1. The structures of these genes and the functional motifs and polymorphic variants of their proteins were documented and the features and functions of their proteins were discussed. Phylogenetic analyses based on both nucleotide and protein data demonstrated that HSP90(AA+AB+B) formed a monophyletic clade, whereas TRAP is a relatively distant paralogue of this clade.

Rearing density influences the expression of stress-related genes in sea bass (Dicentrarchus labrax, L.)

The worldwide decline of ocean fisheries stocks has provided a rapid growth in fish farming and the problems connected to animal welfare in aquaculture gained importance. In this context, we have looked for molecular markers among those genes whose expression could reasonably result modified by the different farming conditions. With this purpose, we have evaluated, in liver and brain of sea basses, grown for 3 months at different biomass density (<10, 80 and 100 kg/m3), the expression of those genes coding for proteins related to stress such as Heat Shock Proteins (HSPs), Metallothioneins (MTs) and Cytochrome P4501A (CYP4501A). In liver, the expression of MT and CYP4501A mRNA resulted induced in animals reared at 80 and 100 kg/m3. Inducible HSP70 appeared significantly over expressed only at the biomass of 100 kg/m3, while apparently, no induction was detectable for HSP90. In brain tissue instead, MT and HSP90 were induced already at 80 kg/m3; CYP4501A and HSP70 were influenced only at the higher population density of 100 kg/m3. In the last three decades, there has been an exponential increase in the interest concerning the description, classification and functional significance of stress-related proteins, in particular HSPs. These proteins represent precious biomarkers to evaluate the welfare conditions when they are still recoverable; detecting their mRNA by PCR is fast, easy and relatively inexpensive. Therefore, we propose this method as a good alternative to monitor fish welfare.

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.

The zebrafish as a model system in developmental, toxicological and transgenic research

The zebrafish has long been used as a model system in fisheries biology and toxicology. More recently, it has also become the focus of a major research effort into understanding the molecular and cellular events which dictate the development of vertebrate embryos. As well, the zebrafish has proven attractive in studies examining the factors which affect the creation of transgenic fish and the expression of transgenes. The advances which have been made in these areas have firmly established this small aquarium fish as a major model system in biological and biotechnological research.

The effect of dietary phosphorus on heat shock protein mRNAs during acute heat stress in male broiler chickens (Gallus gallus)

A 2 x 2 factorially arranged completely randomized experimental design was used to study the relationship between inorganic phosphorus (Pi) and heat shock protein (HSP) mRNA expression in different organs of commercial broiler cockerels during acute heat stress (HS). Brain, heart, liver and spleen were assayed for hsp70, hsp90alpha and hsp90beta mRNA. At 1 day of age, chickens were assigned randomly to two dietary Pi treatment groups (Pi-: 0.16%; Pi+: 0.5%). At 3 weeks of age, half of the chickens in each Pi group were subjected to HS (Ta=41 degrees C, 60 min) while the other half was maintained in a thermoneutral environment (CN, Ta=25 degrees C). The results showed inter-organ variation in the expression of HSP mRNAs. Brain expressed the most HSP mRNAs while spleen expressed the least. When broilers were subjected to HS, the expression of HSP mRNAs was influenced positively by the consumption of the Pi+ diet. However, analysis of variance revealed that Ta influenced HSP transcription more than phosphorus availability. Thermal stress caused induction of hsp90alpha and hsp90beta in heart, liver and spleen, but hsp90alpha and hsp9beta mRNA levels were stable in brain. Transcription of hsp70 increased (P< or =0.05) in all organs from chickens in HS groups when compared to chickens in CN groups. Although Pi+ did not show any significant increases in the expression of hsp mRNAs, there were consistently larger HSP mRNA values in liver and spleen tissues. The high expression of hsp90alpha and hsp90beta in brain of chicks in both CN and HS conditions could be due to the involvement of hsp90 in steroid hormone receptors or the high metabolic activity of neurons in the central nervous system.

Evolution of heat shock protein and immunity

Heat shock proteins (hsps) are among the most abundant intracellular proteins. Their synthesis is rapidly up-regulated by various 'stressors' including temperature, glucose deprivation, infection and cancer. Certain hsps are able to: (i). associate and chaperone a large variety of cellular peptides; (ii). be efficiently internalized by antigen presenting cells (APC) through receptor-mediated endocytosis; (iii). channel antigenic peptides they chaperone in the APC's MHC class I presentation pathway; (iv). and stimulate inflammatory cytokines, chemokines and co-stimulatory molecules through the NFkappab signaling pathway. Extracellular release of hsps upon necrotic cell death and their modulated access at the surface of some cells, can be considered as a putative 'danger' signal. Based on the ancient origins and structural conservation of hsps, it has been proposed that, the role of hsps in immunity emerged early in evolution and to be widespread in extant organisms. Data from studies with the frog Xenopus support this proposition.

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.

Molecular and cell biology of porcine HSP47 during wound healing: complete cDNA sequence and regulation of gene expression

Heat shock protein (HSP) 47 is a major stress-inducible protein that is localized to the endoplasmic reticulum of avian and mammalian cells and is thought to act as a molecular chaperone specific for the processing of procollagen. However, limited information is available regarding the regulation of HSP47 during wound healing. Using a polymerase chain reaction strategy, screening of a cDNA library, and RACE-polymerase chain reaction approaches, the sequence of a full-length porcine HSP47 cDNA has been identified. The cDNA contained 2096 bp that encodes for an 18 amino acid signal peptide and a mature protein coding region consisting of 401 amino acid residues. It also included 108 bp of the 5' noncoding region and a 731-bp 3' noncoding region. The deduced amino acid is 83% identical to chicken, 87% identical to mouse, 88% identical to rat, and 91% identical to human HSP47. It also shares between 26% and 30% identity with different members of the serine protease inhibitor superfamily. The protein contains a RDEL endoplasmic reticulum retention signal, and two potential glycosylation sites. All of these features are characteristic of HSP47 in higher vertebrates. Heat shock treatment of porcine fibroblasts led to up-regulation of HSP47 at both the transcriptional and translational levels. HSP47 protein levels were also up-regulated during skin wound healing in a pig model. Moreover, a higher molecular weight complex at approximately 140 Kda containing HSP47 was detected at the stage of healing that was coincident with the maximal transcriptional expression of HSP47 during wound healing in this animal model. Further investigation of how HSP47 is regulated during normal and abnormal skin wound healing may lead to new therapeutic approaches to improve the healing process.

Effects of endosulfan and nonylphenol on the primordial germ cell population in pre-larval zebrafish embryos

A variety of chemicals released into the aquatic environment are capable of targeting the reproductive system in fish and other vertebrates. Some of the effects observed in exposed adults may arise by permanent organizational changes that occur during embryogenesis, including changes in gonad structure and function. Little work has addressed the effects of pesticides and industrial chemicals, many of which are recognized as endocrine disrupting chemicals, on early embryos. The recent cloning of the vasa gene in zebrafish, the mRNA of which is found in fertilized eggs and is later segregated into the primordial germ cells (PGCs), has provided a unique opportunity to examine PGC migration and positioning in early embryos. We utilized antisense RNA probes to vasa mRNA in whole mount in situ hybridization analysis in order to examine the early migration and distribution of PGCs in embryos exposed to endosulfan and nonylphenol. The data reveal that these chemicals cause alterations in the distribution of PGCs along the anterior-posterior axis in 24-h-old embryos. This suggests that the previously reported alterations in juvenile and adult gonad structure of various aquatic vertebrates following exposure to pesticides and industrial chemicals could be related in part to alterations in early PGC distribution.

Identification of two hsp90 genes in carp

Two hsp90 cDNA isoforms (hsp90alpha and hsp90beta) were isolated from the common carp (Cyprinus carpio). Gene-specific probes and primers were selected and used in Northern blot hybridization and RT-PCR reactions to measure the basal hsp90 mRNA levels and to follow the inducer-specific expression of the hsp90 genes in different tissues during in vivo studies. The hsp90beta gene is largely constitutively expressed at a fairly high level in all the examined tissues (brain, liver and kidney) and is slightly inducible by an elevated temperature. Hsp90alpha mRNA is present in the brain, but is hardly detectable in the kidney and liver of unstressed animals. In the brain, this gene is greatly upregulated following thermal stress, whereas in the liver and kidney heat shock has only minor effects on its expression. Hsp90alpha, but not hsp90beta, responds to an elevated level of Cd in a dose-, time- and tissue-dependent manner.

Perinatal expression of heat-shock protein 90 in different regions of the brain and in non-neural tissues of the piglet

Important stressful events occur at birth or within the few hours that follow. To establish a possible involvement of stress proteins, expression of heat-shock protein 90 was determined by Western blotting in several regions of the brain and in non-neural tissues of the developing piglet (fetal to 10 days and adult). Expression was found in all the tissues studied. While comparable values were found in the whole brain during development, decreased expressions were observed from 4 to 8 h to 2 days after birth in cerebellum, cortex, hypothalamus and striatum. In hippocampus, low expression was observed from 4 h postnatally onward. In non-neural tissues, low expression was observed after birth and in the adult for heart, liver and lungs. In kidney, low values were found from birth to 1 day of age. Changes in environmental parameters like temperature and/or hypoxia can be related to differential expressions of heat-shock proteins and they possibly result in severe developmental outcomes. The results are discussed in terms of using the newborn piglet as a model for the study of different forms of stress on the heat-shock protein expression during postnatal development.

Heat shock protein 90 mediates protein-protein interactions between human aminoacyl-tRNA synthetases

Heat shock protein 90 (hsp90) is a molecular chaperone responsible for protein folding and maturation in vivo. Interaction of hsp90 with human glutamyl-prolyl-tRNA synthetase (EPRS) was found by genetic screening, co-immunoprecipitation, and in vitro binding experiments. This interaction was sensitive to the hsp90 inhibitor, geldanamycin, and also ATP, suggesting that the chaperone activity of hsp90 is required for interaction with EPRS. Interaction of EPRS with hsp90 was targeted to the region of three tandem repeats linking the two catalytic domains of EPRS that is also responsible for the interaction with isoleucyl-tRNA synthetase (IRS). Interaction of EPRS and IRS also depended on the activity of hsp90, implying that their association was mediated by hsp90. EPRS and IRS form a macromolecular protein complex with at least six other tRNA synthetases and three cofactors. hsp90 preferentially binds to most of the complex-forming enzymes rather than those that are not found in the complex. In addition, inactivation of hsp90 interfered with the in vivo incorporation of the nascent aminoacyl-tRNA synthetases into the multi-ARS complex. Thus, hsp90 appears to mediate protein-protein interactions of mammalian tRNA synthetases.

Cloning and characterization of salmon hsp90 cDNA: upregulation by thermal and hyperosmotic stress

Accumulating evidence suggests that glucocorticoids are essential for development of hypoosmoregulatory capacity in salmon during adaptation to seawater. Heat shock protein (hsp)90 has been reported to function in signal transduction and the maturation and affinity of glucocorticoid receptors. We sought to determine whether this hsp might be upregulated by thermal and hyperosmotic stress in salmon, a species that migrates between the freshwater and marine environments. A 2625-bp cDNA cloned from a salmon cDNA library was found to code for a protein of 722 amino acids exhibiting a high degree of identity with zebra fish (92%) and human (89%) hsp90beta. Accumulation of hsp90 mRNA was observed in isolated branchial lamellae incubated under hyperosmotic conditions and in branchial lamellae of salmon exposed to hyperosmotic stress in vivo. In contrast, exposure of kidney to hyperosmotic stress in vitro and in vivo failed to elicit an increase in the quantity of hsp90 mRNA. By way of comparison, accumulation of hsp90 mRNA was observed in both branchial lamellae and kidney tissue subjected to thermal stress in vitro and in vivo. Western blot analyses of proteins isolated from tissues under identical conditions in vitro revealed that the pool of hsp90 increased with thermal stress but not with osmotic stress. The results suggest that accumulation of hsp90 mRNA in response to osmotic stress is unrelated to cellular protein denaturation and that synthesis of hsp90 may be regulated at both the level of transcription and translation.

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

To elucidate the potential role of the hsp70 gene family in developmental processes in vertebrates, we chose to study the expression of one of these genes in zebrafish. A zebrafish gastrula cDNA library was screened with a Pleurodeles waltl hsp70 cDNA probe. A 2.3-kb cDNA was thus isolated and sequenced. The predicted amino acid sequence contained an open reading frame encoding for a 649-amino acid polypeptide. Sequence analysis showed strong homology with hsp70-related gene sequences in other species; in particular, the strongest homology was found with the cognate members of this family. Tests of heat inducibility revealed that transcripts were expressed at normal temperature, but the level of transcript expression increased after heat shock. Moreover, experiments of the neosynthesis of total proteins in heat shock conditions and corresponding immunoblotting assays showed that 24-h-stage embryos are able to respond to heat shock. The quantity of 70 kDa proteins, recognized by a specific antibody of the HSP/C70 protein family, is expressed in control condition and increased significantly after heat shock. Furthermore, Northern blot analysis of transcript expression showed that the corresponding mRNAs were detected throughout embryonic development in the absence of any heat shock. Our clone, named hsc70, thus corresponded to a cognate member of the hsp70 gene family, expressed under normal conditions during development, but also heat inducible. The spatio-temporal pattern of transcripts during development was determined by in situ hybridization on wholemount embryos at different stages. As a maternal RNA, hsc70 mRNA was uniformly present in the embryo, up to the end of gastrulation. Later, a tissue-specific enrichment of hsc70 transcripts was detected in the central nervous system (CNS) and in a fraction of the somites. These results suggest that the hsc70 gene may be involved in developmental differentiation events.

hsp47 and hsp70 gene expression is differentially regulated in a stress- and tissue-specific manner in zebrafish embryos

We have examined differences in the spatial and temporal regulation of stress-induced hsp47 and hsp70 gene expression following exposure of zebrafish embryos to heat shock or ethanol. Using Northern blot analysis, we found that levels of hsp47 and hsp70 mRNA were dramatically elevated during heat shock in 2-day-old embryos. In contrast, ethanol exposure resulted in strong upregulation of the hsp47 gene whereas hsp70 mRNA levels increased only slightly following the same treatment. Whole-mount in situ hybridization analysis revealed that hsp47 mRNA was expressed predominantly in precartilagenous cells, as well as several other connective tissue cell populations within the embryo following exposure to either stress. hsp70 mRNA displayed a very different cell-specific distribution. For example, neither stress induced hsp70 mRNA accumulation in precartilagenous cells. However, high levels of hsp70 mRNA were detectable in epithelial cells of the developing epidermis following exposure to heat shock, but not to ethanol. These cells did not express the hsp47 gene following exposure to either of these stresses. The results suggest the presence of different inducible regulatory mechanisms for these genes which operate in a cell- and stress-specific manner in zebrafish embryos.

Sequence features and phylogenetic analysis of the stress protein hsp90alpha in chinook salmon (Oncorhynchus tshawytscha), a poikilothermic vertebrate

We cloned and sequenced a chinook salmon Hsp90 cDNA; sequence analysis shows it to be Hsp90alpha. Phylogenetic analysis supports the hypothesis that alpha and beta paralogs of Hsp90 arose as a result of a gene duplication event and that they diverged early in the evolution of vertebrates, before tetrapods separated from the teleost lineage. Among several differences distinguishing poikilothermic Hsp90alpha sequences from their bird and mammal orthologs, the teleost versions specifically lack a characteristic QTQDQP phosphorylation site near the N-terminus. We used the cDNA to develop an RNA (Northern) blot to quantify cellular Hsp90 mRNA levels. Chinook salmon embryonic (CHSE-214) cells responded to heat shock with a rapid rise in Hsp90 mRNA through 4 h, followed by a gradual decline over the next 20 h. Hsp90 mRNA level may be useful as a stress indicator, especially in a laboratory setting or in response to acute heat stress.

The Hsp90 complex--a super-chaperone machine as a novel drug target

Cells respond to sudden changes in the environmental temperature with increased synthesis of a distinct number of heat shock proteins (Hsps). Analysis of the function of these proteins in recent years has shown that all the major classes of conserved Hsps are molecular chaperones involved in assisting cellular protein folding and preventing irreversible side-reactions, such as unspecific aggregation. In addition to their function under stress conditions, molecular chaperones also play a critical role under physiological conditions. Hsp90 is one of the most abundant chaperones in the cytosol of eukaryotic cells. It is part of the cell's powerful network of chaperones to fight the deleterious consequences of protein unfolding caused by nonphysiological conditions. In the absence of stress, however, Hsp90 is an obligate component of fundamental cellular processes such as hormone signaling and cell cycle control. In this context, several key regulatory proteins, such as steroid receptors, cell cycle kinases, and p53, have been identified as substrates of Hsp90. Recently, Hsp90 was shown to be the unique target for geldanamycin, a potent new anti-tumor drug that blocks cell proliferation. Interestingly, under physiological conditions, Hsp90 seems to perform its chaperone function in a complex with a set of partner proteins, suggesting that the Hsp90 complex is a multi-chaperone machine specialized in guiding the maturation of conformationally labile proteins. The regulation of key signaling molecules of the cell by the Hsp90 machinery is a stimulating new concept emerging from these studies, and Hsp90 has become a promising new drug target.

The 90-kDa molecular chaperone family: structure, function, and clinical applications. A comprehensive review

The 90-kDa molecular chaperone family (which comprises, among other proteins, the 90-kDa heat-shock protein, hsp90 and the 94-kDa glucose-regulated protein, grp94, major molecular chaperones of the cytosol and of the endoplasmic reticulum, respectively) has become an increasingly active subject of research in the past couple of years. These ubiquitous, well-conserved proteins account for 1-2% of all cellular proteins in most cells. However, their precise function is still far from being elucidated. Their involvement in the aetiology of several autoimmune diseases, in various infections, in recognition of malignant cells, and in antigen-presentation already demonstrates the essential role they likely will play in clinical practice of the next decade. The present review summarizes our current knowledge about the cellular functions, expression, and clinical implications of the 90-kDa molecular chaperone family and some approaches for future research.

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.

HSP90alpha gene expression may be a conserved feature of vertebrate somitogenesis

We have previously demonstrated that the hsp90alpha and hsp90beta genes in zebrafish are expressed in dramatically different spatial and temporal patterns in early embryos. In the case of hsp90alpha, expression is spatially restricted within the somites to putative myogenic cells which also express mRNA encoding the myogenic bHLH transcription factor myoD and is downregulated along with myoD following myogenesis. In the present study, we have examined hsp90alpha gene expression in developing chicken embryos using a gene-specific probe. We show that hsp90alpha gene expression is also localized to a subset of cells within the somites of chicken embryos and that the expression pattern correlates closely to that observed for myoD. Furthermore, expression of the hsp90alpha gene is strongly upregulated throughout the embryo following heat shock in a manner similar to that observed in heat-shocked zebrafish embryos. The data suggest that the hsp90alpha gene may play an evolutionarily conserved role during somitogenesis in vertebrates in addition to providing protection to all cells of the embryo following stress.

Expression of genes encoding the collagen-binding heat shock protein (Hsp47) and type II collagen in developing zebrafish embryos

Hsp47 is a heat-shock protein which interacts with newly synthesize procollagen chains in the endoplasmic reticulum (ER) of collagen-secreting cells and is thought to assist in procollagen triple helix assembly and subsequent transport to the cis-Golgi. This is supported by studies which have reported that genes encoding collagen and Hsp47 are subject to co-ordinate increases and decreases in expression in cultured cells. However, limited information is available regarding hsp47 expression in vivo, particularly during early embryonic development when a variety of collagen genes are expressed. Here we show that the zebrafish hsp47 gene is expressed in a dynamic spatiotemporal pattern in developing embryos. Strong expression of hsp47 mRNA is co-incident predominantly with expression of the type II collagen gene (col2a1) in a number of chondrogenic and non-chondrogenic tissues including the notochord, otic vesicle and developing fins. Notochordal expression of both genes is disrupted in floating head (flh) and no tail (ntl) embryos, which lack properly differentiated notochords. Surprisingly, no hsp47 mRNA is detectable in the strongly col2a1-expressing cells of the floor plate and hypochord, indicating that the two genes are not strictly co-regulated. Finally, Northern blot analysis revealed two alternative transcripts of col2a1 which are expressed in distinct temporal patterns. Appearance of the larger transcript occurs following somitogenesis, a time which coincides with the co-activation of hsp47 and col2a1 gene expression in tissues outside of the notochord.

Cloning and characterization of a cDNA encoding the collagen-binding stress protein hsp47 in zebrafish

Hsp47 is a major stress-inducible protein that is localized to the endoplasmic reticulum of avian and mammalian cells and is thought to act as a molecular chaperone specific for the processing of procollagen. Although hsp47 is coordinately expressed together with several collagen types, and vertebrate embryos are known to express collagen genes in complex spatial and temporal patterns, limited information is available regarding the function or regulation of hsp47 during early embryonic development. We have initiated an examination of hsp47 in the zebrafish, Danio rerio, which offers a number of features that make it attractive as a model developmental system with which to examine the expression and function of hsp47. A polymerase chain reaction (PCR)-based cloning strategy was used to isolate a hsp47 cDNA from an embryonic zebrafish cDNA library. The deduced translation product of the cDNA is a 404-amino-acid polypeptide that is 72% identical to chicken, 64% identical to mouse and rat, and 69% identical to human hsp47. The protein contains a typical hydrophobic signal sequence, an RDEL endoplasmic reticulum retention signal, and a serine protease inhibitor signature sequence, all of which are characteristic of hsp47 in higher vertebrates. Thus, it is likely that hsp47 in zebrafish is also localized to the endoplasmic reticulum and may play a similar role to its counterpart in higher vertebrates. Northern blot analysis revealed that the hsp47 gene is expressed at relatively low levels in embryos during normal development but is strongly induced following exposure to heat shock at the gastrula, midsomitogenesis, 2-day, and 3-day larval stages. The level of induction was much higher than has previously been reported in chicken and mouse cells.

Specific localization of zebrafish hsp90 alpha mRNA to myoD-expressing cells suggests a role for hsp90 alpha during normal muscle development

Members of the eukaryotic hsp90 family function as important molecular chaperones in the assembly, folding and activation of a select group of cellular signalling molecules and transcription factors. Several of the molecules with which hsp90 interacts, such as the bHLH transcription factor myoD, are known to be important regulators of developmental events in vertebrates. However, little information is available in support of any specific role for hsp90 in developing embryos in vivo. In this study, we provide the first in vivo evidence that the hsp90 alpha gene may play a role in the process of myogenesis. We show that constitutive hsp90 alpha mRNA in zebrafish embryos is restricted primarily to a subset of cells within the somites and pectoral fin buds which also express myoD. Furthermore, expression of the hsp90 alpha gene is down-regulated along with myoD in differentiated muscles of the trunk at a time when levels of mRNA encoding the muscle structural protein alpha-tropomyosin remain high. No hsp90 alpha mRNA is detectable within the CNS at control temperatures. In contrast, heat shock-induced expression of the hsp90 alpha gene occurs throughout the embryo at all stages of development examined. The expression patterns strongly suggest that the hsp90 alpha gene plays a specific role in the normal process of myogenesis in addition to providing protection to all cells of the embryo during periods of environmental stress.