Ubiquitous and cell-specific members of the avian small heat shock protein family

Differential expression of small heat shock proteins in the brain of broiler embryo; the effects of embryonic thermal manipulation

Broilers are more vulnerable to high temperatures than mammals due to the feather cover, lack of sweat glands, fast growth and intensive breeding in commercial systems. Thermal stresses affect the function of various organs and change the expression profiles of hundreds of genes in the different tissues of broilers. Thermal manipulation (TM) during embryogenesis can increase heat tolerance in growing broilers. Small heat shock proteins (SHSPs) are a group of HSPs which participate in many cellular functions like response to different stressors. However, their role in the thermotolerance has not been fully elucidated. Ninety fertilized eggs were randomly divided into three groups (30 eggs/group; 10 eggs/replicate). Normal control (NC) eggs were incubated at 37.5 °C throughout the incubation period whereas heat stress (HS) and cold stress (CS) groups were kept at 41 °C and 33 °C from 15 to 17th day of incubation for 3 h each day, respectively. On day 20, samples from the cerebrums were harvested for histopathology and mRNA expression analyses of HSPB1, HSPB5, HSPB8, and HSPB9. There were no significant differences in survivability, defected embryos, hatchability, and body weight among treatments. TM had no major deleterious effects on the cerebral tissue except for mild degeneration in the HS group. HSPB1, HSPB5, HSPB8, and HSPB9 were expressed in the presence and absence of TM. All SHSP genes tested were downregulated in response to TM except for HSPB9 which was upregulated in the HS group. The highest change in gene expression due to TM observed for HSPB1. This study presents a broader understanding of mechanisms underlying response to TM in broilers. The results suggest that HSPB1, HSPB5, HSPB8, and HSPB9 are involved in thermotolerance in broilers and SHSPs could be involved in the gene expression profiling of TM. It may propose the use of nutritional supplements in the poultry industry to modulate SHSPs.

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

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

Profiling of differential gene expression in the hypothalamus of broiler-type Taiwan country chickens in response to acute heat stress

Acute heat stress severely impacts poultry production. The hypothalamus acts as a crucial center to regulate body temperature, detect temperature changes, and modulate the autonomic nervous system and endocrine loop for heat retention and dissipation. The purpose of this study was to investigate global gene expression in the hypothalamus of broiler-type B strain Taiwan country chickens after acute heat stress. Twelve 30-week-old hens were allocated to four groups. Three heat-stressed groups were subjected to acute heat stress at 38 °C for 2 hours without recovery (H2R0), with 2 hours of recovery (H2R2), and with 6 hours of recovery (H2R6). The control hens were maintained at 25 °C. At the end, hypothalamus samples were collected for gene expression analysis. The results showed that 24, 11, and 25 genes were upregulated and 41, 15, and 42 genes were downregulated in H2R0, H2R2, and H2R6 treatments, respectively. The expressions of gonadotropin-releasing hormone 1 (GNRH1), heat shock 27-kDa protein 1 (HSPB1), neuropeptide Y (NPY), and heat shock protein 25 (HSP25) were upregulated at all recovery times after heat exposure. Conversely, the expression of TPH2 was downregulated at all recovery times. A gene ontology analysis showed that most of the differentially expressed genes were involved in biological processes including cellular processes, metabolic processes, localization, multicellular organismal processes, developmental processes, and biological regulation. A functional annotation analysis showed that the differentially expressed genes were related to the gene networks of responses to stress and reproductive functions. These differentially expressed genes might be essential and unique key factors in the heat stress response of the hypothalamus in chickens.

Detection of neural activity in the brains of Japanese honeybee workers during the formation of a "hot defensive bee ball"

Anti-predator behaviors are essential to survival for most animals. The neural bases of such behaviors, however, remain largely unknown. Although honeybees commonly use their stingers to counterattack predators, the Japanese honeybee (Apis cerana japonica) uses a different strategy to fight against the giant hornet (Vespa mandarinia japonica). Instead of stinging the hornet, Japanese honeybees form a “hot defensive bee ball” by surrounding the hornet en masse, killing it with heat. The European honeybee (A. mellifera ligustica), on the other hand, does not exhibit this behavior, and their colonies are often destroyed by a hornet attack. In the present study, we attempted to analyze the neural basis of this behavior by mapping the active brain regions of Japanese honeybee workers during the formation of a hot defensive bee ball. First, we identified an A. cerana homolog (Acks = Apis cerana kakusei) of kakusei, an immediate early gene that we previously identified from A. mellifera, and showed that Acks has characteristics similar to kakusei and can be used to visualize active brain regions in A. cerana. Using Acks as a neural activity marker, we demonstrated that neural activity in the mushroom bodies, especially in Class II Kenyon cells, one subtype of mushroom body intrinsic neurons, and a restricted area between the dorsal lobes and the optic lobes was increased in the brains of Japanese honeybee workers involved in the formation of a hot defensive bee ball. In addition, workers exposed to 46°C heat also exhibited Acks expression patterns similar to those observed in the brains of workers involved in the formation of a hot defensive bee ball, suggesting that the neural activity observed in the brains of workers involved in the hot defensive bee ball mainly reflects thermal stimuli processing.

Hsp27 is persistently expressed in zebrafish skeletal and cardiac muscle tissues but dispensable for their morphogenesis

Constitutive expression of Hsp27 has been demonstrated in vertebrate embryos, especially in developing skeletal and cardiac muscle. Results of several previous studies have indicated that Hsp27 could play a role in the development of these tissues. For example, inhibition of Hsp27 expression has been reported to cause defective development of mammalian myoblasts in vitro and frog embryos in vivo. In contrast, transgenic mice lacking Hsp27 develop normally. Here, we examined the distribution of Hsp27 protein in developing and adult zebrafish and effects of suppressing Hsp27 expression using phosphorodiamidate morpholino oligonucleotides (PMO) on zebrafish development. Consistent with our previous analysis of hsp27 messenger RNA expression, we detected the protein Hsp27 in cardiac, smooth, and skeletal muscle of both embryonic and adult zebrafish. However, embryos lacking detectable Hsp27 after injection of antisense hsp27 PMO exhibited comparable heart beat rates to that of control embryos and cardiac morphology was indistinguishable in the presence or absence of Hsp27. Loss of Hsp27 also had no effect on the structure of the skeletal muscle myotomes in the developing embryo. Finally, embryos injected with antisense hsp27 and scrambled control PMO displayed equal motility. We conclude that Hsp27 is dispensable for zebrafish morphogenesis but could play a role in long-term maintenance of heart and muscle tissues.

Analysis of the expression and function of the small heat shock protein gene, hsp27, in Xenopus laevis embryos

In previous studies, the only small HSPs that have been studied in Xenopus laevis are members of the HSP30 family. We now report the analysis of Xenopus HSP27, a homolog of the human small HSP, HSP27. To date the presence of both hsp30 and hsp27 genes has been demonstrated only in minnow and chicken. Xenopus HSP27 cDNA encodes a 213 aa protein that contains an alpha-crystallin domain as well as a polar C-terminal extension. Xenopus HSP27 shares 71% identity with chicken HSP24 but only 19% identity with Xenopus HSP30C. Northern blot analysis revealed that Xenopus HSP27 gene expression was developmentally regulated. Constitutive and heat shock-induced hsp27 mRNA accumulation was first detectable at the early tailbud stage while HSP27 protein was detected at the tadpole stage. Furthermore, hsp27 mRNA was enriched in selected tissues under both control and heat shock conditions. Whole mount in situ hybridization analysis detected the presence of this message in the lens vesicle, heart, head, somites, and tail region. Purified recombinant HSP27 protein displayed molecular chaperone properties since it had the ability to inhibit heat-induced aggregation of target proteins including citrate synthase, malate dehydrogenase and luciferase. Thus, Xenopus HSP27, like HSP30, is a developmentally-regulated heat-inducible molecular chaperone.

Evolutionary diversity of vertebrate small heat shock proteins

All vertebrates express multiple small heat shock proteins (sHsps), which are important components of the cellular chaperoning machinery and display a spectacular diversity of functions. This ranges from remodeling the cytoskeleton and inhibiting apoptosis to serving as structural proteins in eye lens and sperm tail. Most information is available for the 10 known mammalian sHsps, formally named HspB1-B10. Only three of them (Hsp27/B1, alphaA-crystallin/B4, alphaB-crystallin/B5) have been reported from nonmammalian vertebrates, while an apparent paralog, Hsp30/B11, is found in frogs and teleost fish. To reconstruct the evolutionary diversification of the sHsps in vertebrates, we searched for additional sHsps in genome, protein, and EST databases and sequenced some avian and amphibian sHsps (HspB2, Hsp30/B11). The urochordate Ciona intestinalis was included in the search, as the outgroup of vertebrates. Orthologs of seven mammalian sHsps were now found in other vertebrate classes. Two novel sHsps, named HspB11 and HspB12, were recognized in birds, and four novel sHsps, named HspB12-B15, in teleost fish. Secondary structure predictions of orthologous sHsps from different vertebrate classes indicate conservation of the beta-sandwich structure of the functionally important C-terminal "alpha-crystallin domain," while the N-terminal domains generally have alpha-helical structures, despite their pronounced sequence variation. The constructed chordate sHsp tree is supported by shared introns, indels, and diagnostic sequences. The tree distinguishes putative orthologous and paralogous relationships, which will facilitate the functional and structural comparison of the various vertebrate sHsps. The 15 recognized paralogous vertebrate sHsps reflect the period of extensive gene duplications early in vertebrate evolution. Eleven of these sHsps are grouped in a clade that might be specific for chordates. It is inferred that at least 13 intron insertions have occurred during the evolution of chordate sHsp genes, while a single ancient intron is maintained in some lineages, in line with the general trend of massive intron gain before or during early vertebrate radiation. Interesting is the occurrence of several head-to-head located pairs of chordate sHsp genes.

Hsp25, a member of the Hsp30 family, promotes inclusion formation in response to stress

Protein aggregates are oligomeric complexes of misfolded proteins, and serve as the seeds of inclusion bodies termed aggresomes in the cells. Heat shock proteins (Hsps) prevent misfolding and aggregate formation. Here, we found that only avian Hsp25 dominantly accumulated in the aggresomes induced by proteasome inhibition. Molecular cloning of chicken Hsp25 (cHsp25) revealed that it belongs to the Hsp30 family, which is a subfamily of the alpha-crystallin/small Hsp gene family. Unexpectedly, overexpression of cHsp25 into HeLa cells promoted inclusion formation whereas overexpression of mouse Hsp27 and its chicken homologue did not. These results suggest that cHsp25 acts differently from other small Hsps on protein aggregates.

Activation of heat shock genes is not necessary for protection by heat shock transcription factor 1 against cell death due to a single exposure to high temperatures

Heat shock response, which is characterized by the induction of a set of heat shock proteins, is essential for induced thermotolerance and is regulated by heat shock transcription factors (HSFs). Curiously, HSF1 is essential for heat shock response in mammals, whereas in avian HSF3, an avian-specific factor is required for the burst activation of heat shock genes. Amino acid sequences of chicken HSF1 are highly conserved with human HSF1, but those of HSF3 diverge significantly. Here, we demonstrated that chicken HSF1 lost the ability to activate heat shock genes through the amino-terminal domain containing an alanine-rich sequence and a DNA-binding domain. Surprisingly, chicken and human HSF1 but not HSF3 possess a novel function that protects against a single exposure to mild heat shock, which is not mediated through the activation of heat shock genes. Overexpression of HSF1 mutants that could not bind to DNA did not restore the susceptibility to cell death in HSF1-null cells, suggesting that the new protective role of HSF1 is mediated through regulation of unknown target genes other than heat shock genes. These results uncover a novel role of vertebrate HSF1, which has been masked under the roles of heat shock proteins.

Structure and properties of avian small heat shock protein with molecular weight 25 kDa

The primary structure of chicken small heat shock protein (sHsp) with apparent molecular weight 25 kDa was refined and it was shown that this protein has conservative primary structure 74RALSRQLSSG(83) at Ser77 and Ser81, which are potential sites of phosphorylation. Recombinant wild-type chicken Hsp25, its three mutants, 1D (S15D), 2D (S77D+S81D) and 3D (S15D+S77D+S81D), as well as delR mutant with the primary structure 74RALS-ELSSG(82) at potential sites of phosphorylation were expressed and purified. It has been shown that the avian tissues contain three forms of Hsp25 having pI values similar to that of the wild-type protein, 1D and 2D mutants that presumably correspond to nonphosphorylated, mono- and di-phosphorylated forms of Hsp25. Recombinant wild-type protein, its 1D mutant and Hsp25, isolated from chicken gizzard, form stable high molecular weight oligomeric complexes. The delR, 2D and 3D mutants tend to dissociate and exist in the form of a mixture of high and low molecular weight oligomers. Point mutations mimicking phoshorylation decrease chaperone activity of Hsp25 measured by reduction of dithiothreitol induced aggregation of alpha-lactalbumin, but increase the chaperone activity of Hsp25 measured by heat induced aggregation of alcohol dehydrogenase. It is concluded that avian Hsp25 has a more stable quaternary structure than its mammalian counterparts and mutations mimicking phosphorylation differently affect chaperone activity of avian Hsp25, depending on the nature of target protein and the way of denaturing.