The functions of serpin-3, a negative-regulator involved in prophenoloxidase activation and antimicrobial peptides expression of Chinese oak silkworm, Antheraea pernyi

Bombyx mori serpin 3 is involved in innate immunity by interacting with serine protease 7 to regulate prophenoloxidase activation

A subfamily of conserved proteins called serpins plays crucial roles in various physiological functions, particularly in the activation pathway of the serine protease cascade, an essential component of insect innate immunity. Here, we found Bombyx mori serpin 3 (BmSerpin3) was most highly expressed in the fat body, and was up-regulated after exposure to bacteria, fungus and virus. Further, the expression of BmSerpin3 in the hemocytes, fat body, midgut of silkworm larvae, and BmN cells was up-regulated upon Bombyx mori nucleopolyhedrovirus (BmNPV) infection. Through Bac-to-Bac expression system, we obtained the active protein of BmSerpin3, and the enzyme activity assay showed that BmSerpin3 significantly inhibited the activity of both subtilisin and trypsin. In addition, BmSerpin3 could inhibit the activation of prophenoloxidase (PPO) in larvae. The knockdown of BmSerpin3 showed increased phenoloxidase (PO) activity compared to control after BmNPV infection. Ultimately, we confirmed that BmSerpin3 interacts with B. mori Serine Protease 7 (BmSP7). Hence, we hypothesize that BmSerpin3 is involved in innate immunity by interacting with BmSP7 to regulate the PPO activation cascade. Taken together, these results showed that BmSerpin3 play a role in silkworm innate immunity and lay a foundation for studying its functions.

The role of a novel secretory peptidoglycan recognition protein with antibacterial ability from the Chinese Oak Silkworm Antheraea pernyi in humoral immunity

Peptidoglycan recognition proteins (PGRPs) are a family of pattern recognition receptors that play a critical role in the immune response of invertebrates and vertebrates. Herein, the short ApPGRP-D gene was cloned from the model lepidopteran Antheraea pernyi. Quantitative PCR (qPCR) confirmed that ApPGRP-D is an immune-related protein and that the expression of ApPGRP-D can be induced by microorganisms. ApPGRP-D is a broad-spectrum pattern recognition protein that activates the prophenoloxidase cascade activation system and promotes the agglutination of microbial cells. Likely due to its amidase activity, ApPGRP-D can inhibit the growth of E. coli and S. aureus. In addition, we demonstrated for the first time that zinc ions, as important metal coenzymes, could promote multiple functions of ApPGRP-D but not its amidase activity.

Effect of acute exposure of Hg on physiological parameters and transcriptome expression in silkworms (Bombyx mori)

Mercury (Hg) contamination poses a global threat to the environment, given its elevated ecotoxicity. Herein, we employed the lepidopteran model insect, silkworm (Bombyx mori), to systematically investigate the toxic effects of Hg-stress across its growth and development, histomorphology, antioxidant enzyme activities, and transcriptome responses. High doses of Hg exposure induced evident poisoning symptoms, markedly impeding the growth of silkworm larvae and escalating mortality in a dose-dependent manner. Under Hg exposure, the histomorphology of both the midgut and fat body exhibited impairments. Carboxylesterase (CarE) activity was increased in both midgut and fat body tissues responding to Hg treatment. Conversely, glutathione S-transferase (GST) levels increased in the fat body but decreased in the midgut. The transcriptomic analysis revealed that the response induced by Hg stress involved multiple metabolism processes. Significantly differently expressed genes (DEGs) exhibited strong associations with oxidative phosphorylation, nutrient metabolisms, insect hormone biosynthesis, lysosome, ribosome biogenesis in eukaryotes, and ribosome pathways in the midgut or the fat body. The findings implied that exposure to Hg might induce the oxidative stress response, attempting to compensate for impaired metabolism. Concurrently, disruptions in nutrient metabolism and insect hormone activity might hinder growth and development, leading to immune dysfunction in silkworms. These insights significantly advance our theoretical understanding of the potential mechanisms underlying Hg toxicity in invertebrate organisms.

Parasitoid Serpins Evolve Novel Functions to Manipulate Host Homeostasis

Parasitoids introduce various virulence factors when parasitism occurs, and some taxa generate teratocytes to manipulate the host immune system and metabolic homeostasis for the survival and development of their progeny. Host-parasitoid interactions are extremely diverse and complex, yet the evolutionary dynamics are still poorly understood. A category of serpin genes, named CvT-serpins, was discovered to be specifically expressed and secreted by the teratocytes of Cotesia vestalis, an endoparasitoid of the diamondback moth Plutella xylostella. Genomic and phylogenetic analysis indicated that the C. vestalis serpin genes are duplicated and most of them are clustered into 1 monophyletic clade. Intense positive selection was detected at the residues around the P1-P1' cleavage sites of the Cv-serpin reactive center loop domain. Functional analyses revealed that, in addition to the conserved function of melanization inhibition (CvT-serpins 1, 16, 18, and 21), CvT-serpins exhibited novel functions, i.e. bacteriostasis (CvT-serpins 3 and 5) and nutrient metabolism regulation (CvT-serpins 8 and 10). When the host-parasitoid system is challenged with foreign bacteria, CvT-serpins act as an immune regulator to reprogram the host immune system through sustained inhibition of host melanization while simultaneously functioning as immune effectors to compensate for this suppression. In addition, we provided evidence that CvT-serpin8 and 10 participate in the regulation of host trehalose and lipid levels by affecting genes involved in these metabolic pathways. These findings illustrate an exquisite tactic by which parasitoids win out in the parasite-host evolutionary arms race by manipulating host immune and nutrition homeostasis via adaptive gene evolution and neofunctionalization.

Changes of the gene expression in silkworm larvae and Cordyceps militaris at late stages of the pathogenesis

Cordyceps militaris is an entomopathogenic fungus that forms its fruiting body. The gene expression change in C. militaris and silkworm larvae were analyzed using RNA-seq to investigate the relationship of C. militaris with the host, silkworm larvae before the death by mycosis. At 144 h after the injection of C. militaris conidia, genes encoding proteases, protease inhibitors, and cuticle proteins in the fat body of silkworm larvae were upregulated, but genes encoding lipoproteins and other proteins in hemolymph were downregulated. On the other hand, at 168 h after the injection of C. militaris conidia, genes encoding amino acid and oligopeptide transporters and permeases in C. militaris were upregulated, suggesting that C. militaris may use peptides and amino acids in silkworm larvae as a nutrient to grow in vivo. Additionally, one gene cluster composed of genes putatively involved in the degradation of phenolic substrates was also upregulated. The addition of 4,5-dichlorocatechol, an inhibitor of catechol 1,2-dioxygenase, inhibited the in vivo growth of C. militaris, Beauveria bassiana and Metarhizium anisopliae. These results also suggest that the expression of the gene cluster may be crucial for the in vivo growth of C. militaris and entomopathogenic fungi. This study will clarify how C. militaris grows in insect hosts by avoiding host's immune systems.

A TIL-Type Serine Protease Inhibitor Involved in Humoral Immune Response of Asian Corn Borer Ostrinia furnaculis

To elucidate the application value of insect endogenous protease and its inhibitor genes in pest control, we analyzed in detail the transcriptome sequence of the Asian corn borer, Ostrinia furnacalis. We obtained 12 protease genes and 11 protease inhibitor genes, and comprehensively analyzed of their spatiotemporal expression by qRT-PCR. In which, a previous unstudied serine protease inhibitor gene attracted our attention. It belongs to the canonical serine proteinase inhibitor family, a trypsin inhibitor-like cysteine-rich domain (TIL)-type protease inhibitor, but its TIL domain lacks two cysteine residues, and it was named as ACB-TIL. Its expression level is relatively very low in the absence of pathogen stimulation, and can be up-regulated expression induced by Gram-negative bacteria (Escherichia coli), virus (BmNPV), and dsRNA (dsEGFP), but cannot be induced by fungus spores (Metarrhizium anisopliae). Prokaryotic expressed ACB-TIL protein can significantly inhibit the melanization in vitro. Injecting this protein into insect body can inhibit the production of antimicrobial peptides of attacin, lebocin and gloverin. Inhibition of ACB-TIL by RNAi can cause the responses of other immune-, protease- and inhibitor-related genes. ACB-TIL is primarily involved in Asian corn borer humoral immunity in responses to Gram-negative bacteria and viruses. This gene can be a potential target for pest control since this will mainly affect insect immune response.

A Versatile Hemolin With Pattern Recognitional Contributions to the Humoral Immune Responses of the Chinese Oak Silkworm Antheraea pernyi

Hemolin is a distinctive immunoglobulin superfamily member involved in invertebrate immune events. Although it is believed that hemolin regulates hemocyte phagocytosis and microbial agglutination in insects, little is known about its contribution to the humoral immune system. In the present study, we focused on hemolin in Antheraea pernyi (Ap-hemolin) by studying its pattern recognition property and humoral immune functions. Tissue distribution analysis demonstrated the mRNA level of Ap-hemolin was extremely immune-inducible in different tissues. The results of western blotting and biolayer interferometry showed recombinant Ap-hemolin bound to various microbes and pathogen-associated molecular patterns. In further immune functional studies, it was detected that knockdown of hemolin regulated the expression level of antimicrobial peptide genes and decreased prophenoloxidase activation in the A. pernyi hemolymph stimulated by microbial invaders. Together, these data suggest that hemolin is a multifunctional pattern recognition receptor that plays critical roles in the humoral immune responses of A. pernyi.

Intestinal proteases profiling from Anticarsia gemmatalis and their binding to inhibitors

Although the importance of intestinal hydrolases is recognized, there is little information on the intestinal proteome of lepidopterans such as Anticarsia gemmatalis. Thus, we carried out the proteomic analysis of the A. gemmatalis intestine to characterize the proteases by LC/MS. We examined the interactions of proteins identified with protease inhibitors (PI) using molecular docking. We found 54 expressed antigens for intestinal protease, suggesting multiple important isoforms. The hydrolytic arsenal featured allows for a more comprehensive understanding of insect feeding. The docking analysis showed that the soybean PI (SKTI) could bind efficiently with the trypsin sequences and, therefore, insect resistance does not seem to involve changing the sequences of the PI binding site. In addition, a SERPIN was identified and the interaction analysis showed the inhibitor binding site is in contact with the catalytic site of trypsin, possibly acting as a regulator. In addition, this SERPIN and the identified PI sequences can be targets for the control of proteolytic activity in the caterpillar intestine and serve as a support for the rational design of a molecule with greater stability, less prone to cleavage by proteases and viable for the control of insect pests such as A. gemmatalis.

Chromosome-level genome assembly of Paralithodes platypus provides insights into evolution and adaptation of king crabs

The blue king crab, Paralithodes platypus, which belongs to the family Lithodidae, is a commercially and ecologically important species. However, a high-quality reference genome for the king crab has not yet been reported. Here, we assembled the first chromosome-level blue king crab genome, which contains 104 chromosomes and an N50 length of 51.15 Mb. Furthermore, we determined that the large genome size can be attributed to the insertion of long interspersed nuclear elements and long tandem repeats. Genome assembly assessment showed that 96.54% of the assembled transcripts could be aligned to the assembled genome. Phylogenetic analysis showed the blue king crab to have a close relationship with the Eubrachyura crabs, from which it diverged 272.5 million years ago. Population history analyses indicated that the effective population of the blue king crab declined sharply and then gradually increased from the Cretaceous and Neogene periods, respectively. Furthermore, gene families related to developmental pathways, steroid and thyroid hormone synthesis, and inflammatory regulation were expanded in the genome, suggesting that these genes contributed substantially to the environmental adaptation and unique body plan evolution of the blue king crab. The high-quality reference genome reported here provides a solid molecular basis for further study of the blue king crab's development and environmental adaptation.

A novel hexamerin with an unexpected contribution to the prophenoloxidase activation system of the Chinese oak silkworm, Antheraea pernyi

Hexamerin was originally identified as a storage protein but later confirmed to be involved in many physiological processes. In the present study, we cloned and characterized a novel hexamerin complementary DNA sequence from the Chinese oak silkworm, Antheraea pernyi (Ap-hexamerin), which shows high homology with reported insect methionine-rich hexamerins. The tissue distribution and time course of expression demonstrated that Ap-hexamerin was predominantly synthesized in the fat body and the expression level was significantly increased in response to the microbial challenge, suggesting the relevance of Ap-hexamerin to immune responses. In further immune functional studies, Ap-hexamerin was confirmed to take part in the upregulation of prophenoloxidase (PPO) activation in A. pernyi haemolymph triggered by pathogen-associated molecular patterns (PAMPs). Additional molecular interaction analysis revealed that Ap-hexamerin is capable of binding the PAMPs used in the phenoloxidase assay, suggesting hexamerin in A. pernyi may positively regulate haemolymph PPO activation, acting as a pattern recognition protein.

Life history alterations upon oral and hemocoelic bacterial exposure in the butterfly Melitaea cinxia

Life history strategies often shape biological interactions by specifying the parameters for possible encounters, such as the timing, frequency, or way of exposure to parasites. Consequentially, alterations in life-history strategies are closely intertwined with such interaction processes. Understanding the connection between life-history alterations and host-parasite interactions can therefore be important to unveil potential links between adaptation to environmental change and changes in interaction processes. Here, we studied how two different host-parasite interaction processes, oral and hemocoelic exposure to bacteria, affect various life histories of the Glanville fritillary butterfly Melitaea cinxia. We either fed or injected adult butterflies with the bacterium Micrococcus luteus and observed for differences in immune defenses, reproductive life histories, and longevity, compared to control exposures. Our results indicate differences in how female butterflies adapt to the two exposure types. Orally infected females showed a reduction in clutch size and an earlier onset of reproduction, whereas a reduction in egg weight was observed for hemocoelically exposed females. Both exposure types also led to shorter intervals between clutches and a reduced life span. These results indicate a relationship between host-parasite interactions and changes in life-history strategies. This relationship could cast restrictions on the ability to adapt to new environments and consequentially influence the population dynamics of a species in changing environmental conditions.

Silkworm serpin32 functions as a negative-regulator in prophenoloxidase activation

The extracellular serine protease cascade is an essential component of insect humoral immunity. Serine protease inhibitors (serpins) play an important regulatory role in the process of insect immunity by regulating the serine protease cascade pathway. We aimed to clarify the function of Bmserpin32 in this study. First, we performed homologous sequence alignment and phylogenetic analysis of Bmserpin32. Bmserpin32 was found to share 64% amino acid sequence identity with Manduca sexta serpin7, an immunomodulatory protein. Bmserpin32 cDNA was cloned, and the recombinant Bmserpin32 protein was expressed in Escherichia coli and purified by nickel-nitrilotriacetic acid affinity and gel filtration chromatography. The activity assay showed that Bmserpin32 had significant inhibitory activity against trypsin. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry and site-directed mutagenesis combined with activity assays indicated that the cleavage site of Bmserpin32 is between Arg³⁵⁹ and Ile³⁶⁰. After infection with E. coli or Micrococcus luteus, the expression level of Bmserpin32 in immune-related tissues was significantly upregulated. In addition, Bmserpin32 could delay or inhibit the melanization of hemolymph by inhibiting the activation of prophenoloxidase in larval hemolymph. Furthermore, a physiological target of Bmserpin32 was identified as the clip protease, BmPAP3, an apparent ortholog of M. sexta propenoloxidase-activating protease-3. Our observations enable a better understanding of the physiological role of Bmserpin32 in regulating melanization in silkworm.

Aedes aegypti vector competence studies: A review

Aedes aegypti is the primary transmitter of the four viruses that have had the greatest impact on human health, the viruses causing yellow fever, dengue fever, chikungunya, and Zika fever. Because this mosquito is easy to rear in the laboratory and these viruses grow in laboratory tissue culture cells, many studies have been performed testing the relative competence of different populations of the mosquito to transmit many different strains of viruses. We review here this large literature including studies on the effect of the mosquito microbiota on competence. Because of the heterogeneity of both mosquito populations and virus strains used, as well as methods measuring potential to transmit, it is very difficult to perform detailed meta-analysis of the studies. However, a few conclusions can be drawn: (1) almost no population of Ae. aegypti is 100% naturally refractory to virus infection. Complete susceptibility to infection has been observed for Zika (ZIKV), dengue (DENV) and chikungunya (CHIKV), but not yellow fever viruses (YFV); (2) the dose of virus used is directly correlated to the rate of infection; (3) Brazilian populations of mosquito are particularly susceptible to DENV-2 infections; (4) the Asian lineage of ZIKV is less infective to Ae. aegypti populations from the American continent than is the African ZIKV lineage; (5) virus adaptation to different species of mosquitoes has been demonstrated with CHIKV; (6) co-infection with more than one virus sometimes causes displacement while in other cases has little effect; (7) the microbiota in the mosquito also has important effects on level of susceptibility to arboviral infection; (8) resistance to virus infection due to the microbiota may be direct (e.g., bacteria producing antiviral proteins) or indirect in activating the mosquito host innate immune system; (9) non-pathogenic insect specific viruses (ISVs) are also common in mosquitoes including genome insertions. These too have been shown to have an impact on the susceptibility of mosquitoes to pathogenic viruses. One clear conclusion is that it would be a great advance in this type of research to implement standardized procedures in order to obtain comparable and reproducible results.

Characterization and functional analysis of serpin-28 gene from silkworm, Bombyx mori

Serine protease inhibitors (Serpins) are a broadly distributed superfamily of proteins with a SERPIN domain and participate in several immune responses. In this study, a serpin-28 gene was identified in B. mori and its role in immune regulation was investigated. This gene has an open reading frame of 1065 bp that encodes a 354-amino acid residue polypeptide containing one SERPIN domain with a predicted molecular weight of 40.3 kDa. Recombinant Bmserpin-28 protein was expressed in Escherichia coli and used to raise rabbit anti-Bmserpin-28 polyclonal antibodies. Quantitative real-time PCR analysis revealed that Bmserpin-28 was expressed in all examined tissues, with maximum expression in the fat body and silk gland. Expression pattern of different developmental stages showed that the highest expression level was in the pupae, while the lowest expression level was recorded at the egg stage. After challenge with four different microorganisms (Escherichia coli, Beauveria bassiana, Micrococcus luteus and B. mori nuclear polyhedrosis virus), the expression pattern of Bmserpin-28 was investigated in fat body and haemocyte samples. A substantial upregulation of Bmserpin-28 expression level was recorded following pathogen challenge in both the tested tissues. Furthermore, RNA interference of Bmserpin-28 resulted in significant upregulation of antimicrobial peptide genes. In summary, our results indicated that Bmserpin-28 may be involved in the innate immunity of B. mori.

Production of functional human CuZn-SOD and EC-SOD in bitransgenic cloned goat milk

Human copper/zinc superoxide dismutase (CuZn-SOD) and extracellular superoxide dismutase (EC-SOD) are two superoxide dismutases that scavenge reactive oxygen species (ROS). Their biological role of eliminating oxidative stress caused by excessive ROS levels in living organisms has been utilized in medical treatment, preventing skin photoaging and food preservation. In this study, we employed two sequences that encode human CuZn-SOD and EC-SOD, along with goat beta-casein 5' and 3' regulatory elements, to construct mammary gland-specific expression vectors. Bitransgenic goats were generated using somatic cell nuclear transfer (SCNT), which employed co-transfection to generate bitransgenic goat fetal fibroblast cells as donor cells, and the expression of human CuZn-SOD and EC-SOD and their biological activities were assayed in the milk. PCR and Southern blot analysis confirmed that the cloned goat harbors both hCuZn-SOD and hEC-SOD transgenes. rhCuZn-SOD and rhEC-SOD were expressed in the mammary glands of bitransgenic goat, as determined by western blotting. The expression levels were 100.14 ± 5.09 mg/L for rhCuZn-SOD and 279.10 ± 5.38 mg/L for rhEC-SOD, as determined using ELISA. A total superoxide dismutase assay with WST-8 indicates that the biological activity of rhCuZn-SOD and rhEC-SOD in goat milk is 1451 ± 136 U/mL. The results indicate that two expression vectors can simultaneously transfect goat fetal fibroblast cells as donor cells to produce transgenic goats by SCNT, and the CuZn-SOD and EC-SOD proteins secreted in the mammary glands showed biological activity. The present study thus describes an initial step in the production of recombinant human SODs that may potentially be used for therapeutic purposes.

Innate immune responses in the Chinese oak silkworm, Antheraea pernyi

Innate immunity, the evolutionarily conserved defense system, has been extensively analyzed in insect models over recent decades. The significant progress in this area has formed our dominant conceptual framework of the innate immune system, but critical advances in other insects have had a profound impact on our insights into the mystery of innate immunity. In recent years, we focused on the immune responses in Antheraea pernyi, an important commercial silkworm species reared in China. Here, we review the immune responses of A. pernyi based on immune-related gene-encoded proteins that are divided into five categories, namely pattern recognition receptors, hemolymph proteinases and their inhibitors, prophenoloxidase, Toll pathway factors and antimicrobial peptides, and others. Although the summarized information is limited since the research on A. pernyi immunity is in its infancy, we hope to provide evidence for further exploration of innate immune mechanisms.

Cloning and characterization of an insect apolipoprotein (apolipophorin-II/I) involved in the host immune response of Antheraea pernyi

Apolipoproteins are protein components of lipoprotein particles, and are increasingly recognized to be functioning in the innate immune systems of both insects and mammals. Mammalian apolipoprotein B (apoB) is associated with a diverse range of innate immune defenses including suppression of bacterial pathogenesis, virus toxicity neutralization, and inhibition of cytokine releases from immune cells. However, little is known about apoB homologous insect apolipophorin-II/I (apoLp-II/I) in controlling of specific pathogen-host encounters such as microbial infections. In the present study, we describe cDNA cloning and characterization of an apoLp-II/I from Chinese oak silk worm, Antheraea pernyi. The apoLp-II/I cDNA is 10237bp in length, which possesses an open reading frame encoding 3305 amino acids. A consensus cleavage site RGRR presenting from Arg⁷¹⁰ to Arg⁷¹³ implies posttranslational cleavage of this protein. Ap-apoLp-II/I shares high sequence identities with apoLp-II/I in lepidoptera and other insects. In addition, considerable similarities also exist between Ap-apoLp-II/I and human apoB, which basically positioned in first 1000 residues of the amino termini. Tissue distribution and time-course expression results demonstrate that Ap-apoLp-II/I transcripts were detected predominantly in the fat body, less in epidermis and rarely in midgut, while the synthetic apoLp-II/I protein was abundant in hemocytes and plasma instead of the fatbody. Expression of Ap-apoLp-II/I was stimulated in response to bacterial challenge. In addition, our preliminary studies established a novel role for Ap-apoLp-II/I in regulating prophenoloxidase activation system. Taken together, apoLp-II/I may play an essential role in innate responses of Antheraea pernyi.

Characterization and expression analysis of serpinB3, the first clade B serine protease inhibitor in Pacific white shrimp, Litopenaeus vannamei

Currently, about nine serpin clades (A-I) were preferentially observed in higher animals and clustered on the basis of function. Of these, eight clades contain extracellular proteins, while clade B contains predominantly intracellular proteins. In the present study, the first clade B serpin (named LvserpinB3) was identified from the Pacific white shrimp Litopenaeus vannamei. LvserpinB3 encoded a 412-amino acid protein with a 19-amino acid signal peptide and a serpin domain. Moreover, a transmembrane helix (TMHs) was predicted to be located on the N-terminal of LvserpinB3. Alignment with the cDNA sequence indicated that the genomic LvserpinB3 gene contains 2 exons and 1 intron. The P1-P1' scissile bond of the core feature reactive center loop (RCL) represented for Arginine-Isoleucine (RI), which was in accordance with PmserpinB3, Msserpin-4, -5 and -7. The highest mRNA expression level of LvserpinB3 was detected in hepatopancreas. A significant decrease of LvserpinB3 was detected in hepatopancreas at 6 h post Vibrio anguillarum injection, and later on, the expression of LvserpinB3 was remarkably elevated at 24 h post bacterial challenge. Suppression of LvserpinB3 in vivo by double-stranded RNA (dsRNA) mediated RNA interference (RNAi) led to a significant increase in the transcripts of LvSP1 (Serine protease 1), LvPPAE2 (Prophenoloxidase-activating Enzyme 2) and cumulative mortality. Furthermore, rLvserpinB3 protein was expressed and purified in vitro for the prophenoloxidase inhibition assay. The rLvserpinB3 protein can strongly impede the extent of proPO cascade. All above imply that LvserpinB3 might be an inhibitor for prophenoloxidase-activating system.