Comparative analysis on the expression of inducible HSPs in the silkworm, Bombyx mori

Comparative transcriptome analysis of false codling moth, Thaumatotibia leucotreta in response to high and low-temperature treatments

The false codling moth (FCM), Thaumatotibia leucotreta, is a major quarantine pest native to Africa. Physical postharvest phytosanitary measures such as cold and heat treatments are championed to control its spread to new regions. However, the molecular changes that T. leucotreta undergoes as it attempts to adjust to its surroundings during the treatments and withstand the extreme temperatures remain largely unknown. The current study employs RNA-seq using the next-generation Illumina HiSeq platform to produce transcriptome profiles for differential gene expression analysis of T. leucotreta larvae under thermal stress. The transcriptome assembly analysis revealed 226,067 transcripts, clustering into 127,018 unigenes. In comparison to the 25 °C treated group, 874, 91, 159, and 754 individual differentially expressed genes (DEGs) co-regulated at -10, 0, 40, and 50 °C, respectively were discovered. Annotation of the DEGs by gene ontology (GO) revealed several genes, previously implicated in low and high-temperature stresses, including heat shock proteins, cytochrome P450, cuticle proteins, odorant binding proteins, and immune system genes. Kyoto Encyclopedia of Genes and Genomics (KEGG) classification analysis revealed that substantive DEGs were those involved in metabolic pathways such as thiamine, purine, folate, and glycerolipid metabolism pathways. The RT-qPCR validation of several significantly up- and down-regulated DEGs showed congruence between RNA-seq and qPCR data. This baseline study lays a foundation for future research into the molecular mechanisms underlying T. leucotreta's cold/heat tolerance by providing a thorough differential gene expression analysis that has identified multiple genes that may be associated with the insect's ability to withstand cold and heat.

The Bombyx mori singed Gene Is Involved in the High-Temperature Resistance of Silkworms

Temperature is an important factor in the growth, development, survival, and reproduction of organisms. The high-temperature resistance mechanism of insects may be significant for use in the prevention and control of insect pests. The silkworm, Bombyx mori, is an important Lepidoptera model species for studies on pest control in agriculture and forestry. We identified a gene in B. mori, the B. mori singed (Bmsn) gene, which is involved in the high-temperature resistance of silkworms. Sn proteins are highly conserved among species in many taxonomic groups. The overexpression of the Bmsn gene promoted the proliferation of silkworm cells, reduced oxidation, and reduced the accumulation of reactive oxygen species under stress. Interfering with the Bmsn gene had the opposite result. We constructed a transgenic B. mori strain that overexpressed the Bmsn gene. The physiological traits of the transgenic strain were significantly improved, and it had stronger high-temperature resistance. The Bmsn gene is involved in the process by which fat bodies respond to high-temperature stress. These findings provide insights into the mechanism of high-temperature resistance of insects and offer a new perspective on agricultural and forestry pest control.

Integrative Analyses of Transcriptomics and Metabolomics in Immune Response of Leguminivora glycinivorella Mats to Beauveria bassiana Infection

This study utilized Beauveria bassiana to infect Leguminivora glycinivorella, analyzed the effects on the transcriptome and metabolome, and further investigated the antibacterial function of L. glycinivorella. We performed transcriptome and metabolome sequencing on the L. glycinivorella infected with B. bassiana and its control groups, and performed a joint analysis of transcriptome and metabolome results. Upon screening, 4560 differentially expressed genes were obtained in the transcriptome and 71 differentially expressed metabolites were obtained in the metabolome. On this basis, further integration of the use of transcriptomics and metabonomics combined an analysis of common enrichments of pathways of which there were three. They were glutathione S-transferase (GSTs) genes, heat shock protein (HSP) genes, and cytochrome P450 (CYP450) genes. These three pathways regulate the transport proteins, such as ppars, and thus affect the digestion and absorption of sugars and fats, thus regulating the development of pests. The above conclusion indicates that B. bassiana can affect the sugar metabolism, lipid metabolism, and amino acid metabolism pathways of L. glycinivorella, and can consume the necessary energy, protein, and lipids of L. glycinivorella. The research on the immune response mechanism of pests against pathogens can provide an important scientific basis and target for the development of immunosuppressants. This study laid an information foundation for the application of entomogenous fungi to control soybean borer at the molecular level.

Influence of temperature variation on gene expression and cocoon production in Bombyx mori Linnaeus, 1758 (Lepidoptera: Bombycidae)

Silkworms (Bombyx mori) are lepidopterans of economic importance for global silk production. However, factors that directly affect the yield and quality of silkworm cocoon production, such as diseases and temperature fluctuations, cause great economic losses. Knowing how they respond to rearing temperature during the most critical stage of their life cycle (i.e., fifth instar) could provide information on their adaptation and improve silk production. In the current work, we analyzed transcriptional data from two groups of B. mori that were reared at 26 °C and 34 °C throughout the fifth instar. The silkworms and cocoons were weighed. In total, 3115 transcripts were differentially expressed (DE; including 1696 down-regulated and 1419 up-regulated) among the 29,157 sequences found by transcriptome assembly. We emphasize the genes associated with immunological response, transcription factors, silk biosynthesis, and heat shock proteins, among the DE transcripts in response to the temperature conditions. Silkworms reared at 34 °C presented a reduced mean body weight (-0.944 g in comparison to the 26 °C group), which had a direct impact on the weight of cocoons formed and the silk conversion rate. These changes were statistically significant when compared to silkworms reared at 26 °C. Mortality rates (6 and 9 %, at 26 °C and 34 °C, respectively) were similar to those obtained in breeding fields. The findings provide information on the biological processes involved in the temperature response mechanism of silkworms, as well as information that may be used in future climatization processes at rearing facilities and in breeding for improved thermotolerance.

Transcription dynamics of heat shock proteins in response to thermal acclimation in Ostrinia furnacalis

Acclimation to abiotic stress plays a critical role in insect adaption and evolution, particularly during extreme climate events. Heat shock proteins (HSPs) are evolutionarily conserved molecular chaperones caused by abiotic and biotic stressors. Understanding the relationship between thermal acclimation and the expression of specific HSPs is essential for addressing the functions of HSP families. This study investigated this issue using the Asian corn borer Ostrinia furnacalis, one of the most important corn pests in China. The transcription of HSP genes was induced in larvae exposed to 33°C. Thereafter, the larvae were exposed to 43°C, for 2 h, and then allowed to recover at 27 C for 0, 0.5, 1, 2, 4, 6, and 8 h. At the recovery times 0.5–4 h, most population tolerates less around 1–3 h than without recovery (at 0 h) suffering continuous heat stress (43 C). There is no difference in the heat tolerance at 6 h recovery, with similar transcriptional levels of HSPs as the control. However, a significant thermal tolerance was observed after 8 h of the recovery time, with a higher level of HSP70. In addition, the transcription of HSP60 and HSC70 (heat shock cognate protein 70) genes did not show a significant effect. HSP70 or HSP90 significantly upregulated within 1–2 h sustained heat stress (43 C) but declined at 6 h. Our findings revealed extreme thermal stress induced quick onset of HSP70 or HSP90 transcription. It could be interpreted as an adaptation to the drastic and rapid temperature variation. The thermal tolerance of larvae is significantly enhanced after 6 h of recovery and possibly regulated by HSP70.

Protein and volatile contents in the mandibular gland of the sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae)

The sugarcane borer Diatraea saccharalis (Lepidoptera: Crambidae) is an important sugarcane pest and mechanical injuries caused through the mandibles can allow pathogen infections. The mandibles of D. saccharalis, as well as other insects, are associated with mandibular glands with a possible function in food intake and mouthparts lubrication; however, the chemical composition of the secretion is poorly known and its elucidation is important for the comprehensive understanding of plant-insect interactions. This study characterized some proteins and volatiles in the mandibular glands of D. saccharalis larvae. MALDI-TOF/TOF mass spectrometry allowed the identification of 24 predicted proteins within 10 functional classes, including the transport and metabolism of carbohydrates, lipids, amino acids, and nucleotides; Posttranslational protein modifications; energy conversion; intracellular trafficking; transcription; translation; and cytoskeleton function. Metabolites identified from GC/MS analysis revealed the presence of hydrocarbons classified as alcohols, ether, alkanes, and esters with differences in their relative abundance. Linolenic acid, the most abundant metabolite found in this gland, when conjugated with amino acids, can be an elicitor in the plant-herbivore interaction. The results suggest the occurrence of digestive and defensive biochemical components, which may contribute to understanding of the multifunctional roles of the mandibular gland secretion of D. saccharalis larvae during feeding activity.

Comparison of gene expression in the red imported fire ant (Solenopsis invicta) under different temperature conditions

The red imported fire ant (RIFA), Solenopsis invicta Buren is native to South America and is known as a global problematic invasive species. This study focused on the molecular response of RIFA by comparing gene expression profiles after exposing ants to low (10 °C) and high (40 °C) temperature stress and comparing them to untreated controls (30 °C). A total of 99,085 unigenes (the clustered non-redundant transcripts that are filtered from the longest assembled contigs) were obtained, of which 19,154 were annotated with gene descriptions, gene ontology terms, and metabolic pathways. 86 gene ontology (GO) functional sub-groups and 23 EggNOG terms resulted. Differentially expressed genes (DEGs) with log₂FC ≥ 10 were screened and were compared at different temperatures. We found 203, 48, and 66 specific DEGs co-regulated at 10, 20, and 40 °C. Comparing transcriptome profiles for differential gene expression resulted in various DE genes, including cytochrome P450, NADH dehydrogenase subunit 1, cuticle protein and heat shock protein (HSP), which have previously been reported to be involved in cold and high temperature resistance. GO analysis revealed that antioxidant activity is up-regulated under high temperature stress. We verified the RNA-seq data by qPCR on 20 up- and down-regulated DEGs. These findings provide a basis for future understanding of the adaptation mechanisms of RIFA and the molecular mechanisms underlying the response to low and high temperatures.

Insect responses to heat: physiological mechanisms, evolution and ecological implications in a warming world

Surviving changing climate conditions is particularly difficult for organisms such as insects that depend on environmental temperature to regulate their physiological functions. Insects are extremely threatened by global warming, since many do not have enough physiological tolerance even to survive continuous exposure to the current maximum temperatures experienced in their habitats. Here, we review literature on the physiological mechanisms that regulate responses to heat and provide heat tolerance in insects: (i) neuronal mechanisms to detect and respond to heat; (ii) metabolic responses to heat; (iii) thermoregulation; (iv) stress responses to tolerate heat; and (v) hormones that coordinate developmental and behavioural responses at warm temperatures. Our review shows that, apart from the stress response mediated by heat shock proteins, the physiological mechanisms of heat tolerance in insects remain poorly studied. Based on life-history theory, we discuss the costs of heat tolerance and the potential evolutionary mechanisms driving insect adaptations to high temperatures. Some insects may deal with ongoing global warming by the joint action of phenotypic plasticity and genetic adaptation. Plastic responses are limited and may not be by themselves enough to withstand ongoing warming trends. Although the evidence is still scarce and deserves further research in different insect taxa, genetic adaptation to high temperatures may result from rapid evolution. Finally, we emphasize the importance of incorporating physiological information for modelling species distributions and ecological interactions under global warming scenarios. This review identifies several open questions to improve our understanding of how insects respond physiologically to heat and the evolutionary and ecological consequences of those responses. Further lines of research are suggested at the species, order and class levels, with experimental and analytical approaches such as artificial selection, quantitative genetics and comparative analyses.

Comparative Analysis of Transcriptome Responses to Cold Stress in Galeruca daurica (Coleoptera: Chrysomelidae)

Galeruca daurica (Joannis) has become a new insect pest in the Inner Mongolia grasslands since 2009, and its larvae and eggs have strong cold tolerance. To get a deeper insight into its molecular mechanisms of cold stress responses, we performed de novo transcriptome assembly for G. daurica by RNA-Seq and compared the transcriptomes of its larvae exposed to five different temperature treatments (-10, -5, 0, 5, and 25°C for 1 h and then recovered at 25°C for 1 h), respectively. Compared with the control (25°C), the numbers of differentially expressed genes (DEGs) decreased from 1,821 to 882, with the temperature declining from 5 to -10°C. Moreover, we obtained 323 coregulated DEGs under different low temperatures. Under four low temperatures (-10, -5, 0, and 5°C), a large number of genes were commonly upregulated during recovery from cold stresses, including those related to cuticle protein, followed by cytochrome P450, clock protein, fatty acid synthase, and fatty acyl-CoA reductase; meanwhile, lots of genes encoding cuticle protein, RNA replication protein, RNA-directed DNA polymerase, and glucose dehydrogenase were commonly downregulated. Our findings provide important clues for further investigations of key genes and molecular mechanisms involved in the adaptation of G. daurica to harsh environments.

Molecular cloning and functional analysis of small heat shock protein 19.1 gene from the Chinese oak silkworm, Antheraea pernyi

Small heat shock proteins (sHSPs) are a class of highly conserved proteins that are ubiquitously found in all types of organisms, from prokaryotes to eukaryotes. In the current study, we identified and characterized the full-length cDNA encoding sHSP 19.1 from the oak silkworm, Antheraea pernyi. Ap-sHSP is 510 bp in length, and encodes a protein of 169 amino acid residues. The protein contains conserved domains found in insect sHSPs, and it belongs to the α-crystallin-HSPs_p23-like superfamily. Recombinant Ap-sHSP was expressed in Escherichia coli cells, and a rabbit anti-Ap-sHSP 19.1 antibody was generated to confirm the biological functions of Ap-sHSP 19.1 in A. pernyi. Real-time polymerase chain reaction and western blot analysis revealed that Ap-sHSP 19.1 expression was highest in the fat body, followed by the midgut, and the lowest expression was found in the Malpighian tubule. Ap-sHSP 19.1 transcript expression was significantly induced following challenge with microbial pathogens. In addition, the expression of Ap-sHSP 19.1 was strongly induced after heat shock. These results suggest that Ap-sHSP 19.1 plays a crucial role in immune responses and thermal tolerance in A. pernyi.

Cloning & sequence identification of Hsp27 gene and expression analysis of the protein on thermal stress in Lucilia cuprina

Hsp27, a highly conserved small molecular weight heat shock protein, is widely known to be developmentally regulated and heat inducible. Its role in thermotolerance is also implicated. This study is a sequel of our earlier studies to understand the molecular organization of heat shock genes/proteins and their role in development and thermal adaptation in a sheep pest, Lucilia cuprina (blowfly), which exhibits unusually high adaptability to a variety of environmental stresses, including heat and chemicals. In this report our aim was to understand the evolutionary relationship of Lucilia hsp27 gene/protein with those of other species and its role in thermal adaptation. We sequence characterized the Lchsp27 gene (coding region) and analyzed its expression in various larval and adult tissues under normal as well as heat shock conditions. The nucleotide sequence analysis of 678 bps long-coding region of Lchsp27 exhibited closest evolutionary proximity with Drosophila (90.09%), which belongs to the same order, Diptera. Heat shock caused significant enhancement in the expression of Lchsp27 gene in all the larval and adult tissues examined, however, in a tissue specific manner. Significantly, in Malpighian tubules, while the heat-induced level of hsp27 transcript (mRNA) appeared increased as compared to control, the protein level remained unaltered and nuclear localized. We infer that Lchsp27 may have significant role in the maintenance of cellular homeostasis, particularly, during summer months, when the fly remains exposed to high heat in its natural habitat.

Gene expression patterns in response to pathogen challenge and interaction with hemolin suggest that the Yippee protein of Antheraea pernyi is involved in the innate immune response

Yippee was first identified as a protein that physically interacts with the Hemolin protein of Hyalophora cecropia. In this study, we identified a gene with a 366bp open reading frame (ORF) that encodes a 121 amino acid protein containing a conserved Yippee domain. We named this gene Ap-Yippee (Yippee gene from Antheraea pernyi), and investigated the role of the protein in the host immune response. A recombinant Ap-Yippee protein was expressed in Escherichia coli cells, and polyclonal antibodies were produced against the recombinant protein. Real-time PCR and a Western blot analysis revealed that Ap-Yippee is expressed in the hemocytes, Malpighian tubules, midgut, silk gland, epidermis, and fat bodies of A. pernyi, with the highest expression level observed in Malpighian tubules. The fifth instar larvae of A. pernyi were challenged by injecting them with nucleopolyhedrovirus (AP-NPV), the Gram-negative bacterium E. coli, the Gram-positive bacterium Micrococcus luteus, or the entomopathogenic fungus, Beauveria bassiana. These challenges with diverse pathogens resulted in differential expression patterns of the protein. A knockdown of the Ap-Yippee gene by small interfering RNA (siRNA) transfection had a significant influence on the expression of the hemolin in the pupae which was confirmed by qRT-PCR and Western blot. Furthermore, a possible protein-protein interaction between Ap-Yippee and Hemolin was explored by Far-Western blotting. Therefore, our data suggest that the Ap-Yippee protein is involved in a pathway that regulates the immune response of insects.

KPNA3-knockdown eliminates the second heat shock protein peak associated with the heat shock response of male silkworm pupae (Bombyx mori) by reducing heat shock factor transport into the nucleus

In this study, we investigated the role of karyopherin alpha 3 in the heat shock response in male silkworm pupae. Karyopherin alpha recognizes the classical nuclear location sequence on proteins and transports them into the nucleus by forming a trimetric complex with karyopherin beta. Three predicted karyopherin alphas (KPNA1, KPNA2 and KPNA3) have been identified from the silkworm Bombyx mori. Pull-down assay result showed that KPNA3 can pull down heat shock transcription factor (HSF) from proteins extracted from tissues using non-denature lysis buffer. After 45 °C heat shock on male B. mori pupae for 30 min, we identified two heat shock protein (HSP) mRNA expression peaks correlating with HSP19.9, HSP20.4 and HSP25.4 at 4 h (peak 1) and 24 h (peak 2). The second peak was eliminated after knockdown of KPNA3. Similar results were obtained following knockdown of HSF, which is the trans-activating factor of heat shock. However, KPNA3 knockdown was not accompanied by the decreased HSF protein levels at 24 h after heat shock which were observed following HSF knockdown. We also expressed recombinant protein GST-KPNA3 and His-HSF in Escherichia coli to perform GST pull-down assay and the result confirmed the interaction between KPNA3 and HSF. We concluded that KPNA3 knockdown eliminates the second heat shock protein peak in the heat shock response of male silkworm pupae by reducing HSF transport into the nucleus.

BmHSP20.8 is Localized in the Mitochondria and has a Molecular Chaperone Function In Vitro

Heat shock proteins (HSPs) are abundant and ubiquitous in almost all organisms from bacteria to mammals. BmHSP20.8 is a small (sHSP) in Bombyx mori that contains a 561 bp open reading frame that encodes a protein of 186 amino acid residues with a predicted molecular mass of 20.8 kDa. The subcellular localization prediction indicated that BmHSP20.8 is likely distributed in the mitochondria with a 51% probability. To identify the subcellular localization of BmHSP20.8, three recombinant vectors were constructed and used to transfect BmN cells. The cytoplasmic and mitochondrial proteins were extracted 72 h after transfection. The Western blot showed that recombinant BmHSP20.8 exists only in the mitochondria. To locate the mitochondrial localization signal domain of BmHSP20.8 more accurately, we cloned four truncated recombinant vectors. The Western blot analysis of the cytoplasmic and mitochondrial proteins showed that the mitochondrial localization signal domain of BmHSP20.8 is located between amino acids 143 to 186. We constructed the pETduet-HIS-SUMO-BmHSP20.8 vector and a soluble BmHSP20.8 was expressed. In a citrate synthase (CS) thermal aggregation experiment, we found that the recombinant BmHSP20.8 protein can protect CS from aggregating at 43 and 48 °C and thus exhibited molecular chaperone activity. Taken together, the results showed that BmHSP20.8 could be a mitochondrial protein and has a molecular chaperone activity, suggesting an important role in mitochondria.

Inhibitors of eicosanoid biosynthesis influencing the transcripts level of sHSP21.4 gene induced by pathogen infections, in Antheraea pernyi

Small heat shock proteins (sHSPs) can regulate protein folding and protect cells from stress. To investigate the role of sHSPs in the silk-producing insect Antheraea pernyi response to microorganisms, a sHsp gene termed as Ap-sHSP21.4, was identified. This gene encoded a 21.4 kDa protein which shares the conserved structure of insect sHsps and belongs to sHSP21.4 family. Ap-sHSP21.4 was highly expressed in fat body and up-regulated in midgut and fat body of A. pernyi challenged with Escherichia coli, Beauveria bassiana and nuclear polyhedrosis virus (NPV), which was determined by quantitative real-time PCR. Meanwhile, knock down of Ap-sHSP21.4 with dsRNA result in the decrease at the expression levels of several immune response-related genes (defensin, Dopa decarboxylase, Toll1, lysozyme and Kazal-type serine protease inhibitor). Additionally, the impact of eicosanoid biosynthesis on the expression of Ap-sHSP21.4 response to NPV was determined using qPCR, inhibitors of eicosanoid biosynthesis significantly suppress Ap-HSP21.4 expression upon NPV challenge. All together, Ap-sHSP21.4 was involved in the immunity of A. pernyi against microorganism and possibly mediated by eicosanoids pathway. These results will shed light in the understanding of the pathogen-host interaction in A. pernyi.

Insect heat shock proteins during stress and diapause

Insect heat shock proteins include ATP-independent small heat shock proteins and the larger ATP-dependent proteins, Hsp70, Hsp90, and Hsp60. In concert with cochaperones and accessory proteins, heat shock proteins mediate essential activities such as protein folding, localization, and degradation. Heat shock proteins are synthesized constitutively in insects and induced by stressors such as heat, cold, crowding, and anoxia. Synthesis depends on the physiological state of the insect, but the common function of heat shock proteins, often working in networks, is to maintain cell homeostasis through interaction with substrate proteins. Stress-induced expression of heat shock protein genes occurs in a background of protein synthesis inhibition, but in the course of diapause, a state of dormancy and increased stress tolerance, these genes undergo differential regulation without the general disruption of protein production. During diapause, when ATP concentrations are low, heat shock proteins may sequester rather than fold proteins.

Eicosanoids mediate sHSP 20.8 gene response to biotic stress in larvae of the Chinese oak silkworm Antheraea pernyi

Small heat shock proteins (sHSPs) can regulate protein folding and protect cells from stress. To investigate the role of sHSPs in the silk-producing insect Antheraea pernyi (A. pernyi; Lepidoptera: Saturniidae), cDNA encoding HSP20.8 in A. pernyi, termed Ap-sHSP20.8, was identified as a 564 bp ORF. The translated amino acid sequence encoded 187 residues with a calculated molecular mass of 20.8 kDa and an isoelectronic point (pI) of 5.98; the sequence showed homology to sHSP chaperone proteins from other insects. Ap-sHSP20.8 mRNA transcript expression was abundant in the midgut and fat body and found to be both constitutive and inducible by infectious stimuli. Therefore, Ap-sHSP20.8 may play important roles in A. pernyi immune responses under biotic stress. Furthermore, we found that eicosanoids could mediate the induction of Ap-sHSP20.8 in the fat body and midgut. Our findings show that sHSPs may be promising molecules to target in order to cripple immunity in insect pests.

Comparative proteomic analysis reveals the suppressive effects of dietary high glucose on the midgut growth of silkworm

The silkworm, Bombyx mori, is an important model of lepidoptera insect, and it has been used for several models of human diseases. In human being, long-term high-sugar diet can induce the occurrence of diabetes and other related diseases. Interestingly, our experiments revealed the high glucose diet also has a suppressive effect on the development of silkworms. To investigate the molecular mechanism by which high-glucose diet inhibited the midgut growth in silkworms, we employed comparative proteomic analysis to globally identify proteins differentially expressed in normal and high-glucose diet group silkworms. In all, 28 differently proteins were suppressed and 5 proteins induced in high-glucose diet group. Gene ontology analysis showed that most of these differently proteins are mainly involved in metabolic process, catalytic and cellular process. A development related protein, imaginal disk growth factor (IDGF), was further confirmed by western blot exclusively expressing in the normal diet group silkworms. Taken together, our data suggests that IDGF plays a critical role in impairing the development of silkworms by a high-glucose diet.

BIOLOGICAL SIGNIFICANCE

Glucose has been thought to play essential roles in growth and development of silkworm. In this paper, we certified firstly that high-glucose diet can suppress the growth of silkworm, and comparative proteomic was employed to reveal the inhibition mechanism. Moreover, an important regulation related protein (IDGF) was found to involve in this inhibition process. These results will help us get a deeper understanding of the relationship between diet and healthy. Furthermore, IDGF may be the critical protein for reducing the blood sugar in silkworm, and it may be used for screening human hypoglycemic drug. The work has not been submitted elsewhere for publication, in whole or in part, and all the authors have approved the manuscript.

Overexpression of small heat shock protein 21 protects the Chinese oak silkworm Antheraea pernyi against thermal stress

Small heat shock proteins (sHSPs) usually act as molecular chaperones to prevent proteins from being denatured in extreme conditions. We first report the sHSP21 gene, named as Ap-sHSP21, in the Chinese oak silkworm Antheraea pernyi (Lepidoptera: Saturniidae). The full-length cDNA of Ap-sHSP21 is 976 bp, including a 5'-untranslated region (UTR) of 99 bp, a 3'-UTR of 316 bp and an open reading frame (ORF) of 561 bp encoding a polypeptide of 186 amino acids. The deduced A. pernyi sHSP21 protein sequence reveals the percent identity is 82-93% in comparison to other sHSPs from insects. Real-time quantitative reverse transcription-PCR (qRT-PCR) analysis shows that Ap-sHSP21 expression is higher in testis than that in other examined tissues and significantly up-regulated after heat shock. In addition, prokaryotic expression and purification of the Ap-sHSP21 protein were performed. SDS-PAGE and Western blot analysis demonstrated that a 25 kDa recombinant protein was successfully expressed in Escherichia coli cells and the purified recombinant protein was also confirmed to protect restriction enzymes from thermal inactivation. The expression of Ap-sHSP21 was significantly down-regulated after RNA interference, which was confirmed by qRT-PCR and Western blot analysis. All together, these results suggest that Ap-sHSP21 play a key role in thermal tolerance.