Identification of a novel toll gene (Shtoll3) from the freshwater crab Sinopotamon henanense and its expression pattern changes in response to cadmium followed by Aeromonas hydrophila infection

Isolation, cloning, and tissue distribution and functional analysis of ShP-glycoprotein in the freshwater crab Sinopotamon henanense exposed to Cd and Cd-QDs

P-glycoprotein (Pgp), a member of ATP binding cassette (ABC) transporter family, can extrude toxic substances out of cells by mediating multi-xenobiotic resistance (MXR) in aquatic organisms, however, its regulation and association with MXR are still unclear. In this work, the genetic information of Pgp in freshwater crab Sinopotamon henanense (ShPgp) was revealed for the first time. ShPgp with a total of 4488 bp was cloned and analyzed, which includes 4044 bp open reading frame, 353 bp 3' untranslated region, and 91 bp 5' untranslated region. The recombinant ShPGP were expressed in Saccharomyces cerevisiae and taken for SDS-PAGE and western blot analysis. ShPGP was widely expressed in the midgut, hepatopancreas, testis, ovary, gill, hemocytes, accessory gonad and myocardium of the crabs studied. The images of immunohistochemistry indicated that ShPgp was mainly distributed in the cytoplasm and cell membrane. When the crabs were exposed to cadmium or cadmium containing quantum dots (Cd-QDs), not only the relative expression of ShPgp mRNA and the protein produced were enhanced, but also the MXR activity and ATP contents. The relative expression of target genes related to energy metabolism, detoxification and apoptosis was also determined in the carbs exposed to Cd or Cd-QDs. The results showed that bcl-2 was significantly down-regulated, while other genes were up-regulated except PPAR (not affected). However, when the Shpgp in treated crabs was interfering by knockdown technique, their apoptosis and the expression of proteolytic enzyme genes and transcription factors MTF1 and HSF1 were also elevated, while the expression of apoptosis inhibiting and fat metabolism genes were compromised. Based on the observation, we concluded that MTF1 and HSF1 were involved in gene transcription regulation of mt and MXR, respectively, while PPAR had limited regulatory effect on those genes in S. henanense. NF-κB may play a negligible role in the process of apoptosis in testes induced by cadmium or Cd-QDs. However, the detail information regarding Pgp involvement in SOD or MT, and its association with apoptosis during xenobiotics insults remain to be explored.

Identification of acid phosphatase (ShACP) from the freshwater crab Sinopotamon henanense and its expression pattern changes in response to cadmium

Acid phosphatase(ACP) is an important immune enzyme in crustacean humoral immunity. At present, the research on ACP mainly focuses on the biochemical properties of the enzyme, while few studies on gene expression. In this study, ShACP was cloned and the effect of cadmium stress on the expression and function of ShACP in the freshwater crab Sinopotamon henanense was studied. Analysis of the ShACP sequence and tissue distribution results showed that the cDNA sequence of ShACP was 1629 bp, including 48 bp 5' untranslated region, 1209 bp open reading frame region, and 372 bp 3' untranslated region, encoding 402 amino acids. ShACP contained multiple phosphorylation sites and mainly played a role in the hemolymph. Under low-concentration cadmium stress, the body improved immunity by enhancing the expression of ShACP, while high-concentration cadmium stress inhibited the expression of ShACP. ShACP can promote the phagocytosis of hemocytes, while cadmium stress reduced the phagocytosis of hemocytes. This study provides a theoretical basis for further research on the immune system of crabs and is of great significance for the study of crustacean immune responses under heavy metal stress.

Cloning, identification, and functional characterization of novel prophenoloxidases (ShproPO) from the freshwater crab Sinopotamon henanense in response to cadmium exposure and Aeromonas hydrophila infection

Prophenoloxidase (proPO) is essential in the prophenoloxidase-activating system (proPO-AS) which is important for defense against foreign infection in crustaceans. However, most studies have focused on expression in the presence of a single pathogenic bacterium, and very few have addressed the presence of environmental contaminants simultaneously, such as cadmium (Cd) and Aeromonas hydrophila. Our study aimed to investigate the function of proPO in the freshwater crab Sinopotamon henanense and the changes in its expression by Cd and infection of A. hydrophila. A novel proPO from the hemocytes of S. henanense (ShproPO) was found in this research, the full-length cDNA of ShproPO was 2620 bp of encoding a protein of 678 amino acids containing three typical hemocyanin domains. The ShproPO protein could be found in both the granular (GHc) and the semi-granular hemocytes (SGHc). The ShproPO mRNA was found to be abundantly expressed in hemocytes and could be influenced by A. hydrophila infection. These results indicate that ShproPO could be involved in the antibacterial process. Further research found that low concentrations of Cd could promote its expression after infection with A. hydrophila. Therefore, it was hypothesized that Cd disrupted the response of crabs to A. hydrophila infection. Subsequently, PO enzyme activity was found to be significantly reduced through in vivo RNA interference with ShproPO, and the results suggested that ShproPO is likely to be a key enzyme in the melanization response. Finally, ShproPO was found to significantly enhance the phagocytosis of A. hydrophila-infected hemocytes by in vitro recombination, confirming that ShproPO is involved in hemocyte-mediated melanization and phagocytosis. Our findings reveal completely new insight into the immunotoxicity of Cd and the immune function of ShproPO in S. henanense.

A novel type II crustin in the innate immune response of the freshwater crab (Sinopotamon henanense) against infection and its expression changes by cadmium

Antibacterial peptide (AMP), an effector of the innate immune system, is an essential component of invertebrate innate immunity. Crustin is a family of antimicrobial peptides that are widely studied in crustaceans. Here we report a novel crustin (designated Shcrustin) from the freshwater crab Sinopotamon henanense. The results revealed that the full-length cDNA of Shcrustin was 691 bp with an open reading frame (ORF) of 510 bp. Phylogenetic analysis of the Shcrustin sequence showed that it clustered with type II crustin. Shcrustin exists in different tissues, among which the highest expression level is found in the gills. After the bacterial challenge, the expression of Shcrustin increased in hemocytes or gills. However, crustin expression was suppressed in the presence of cadmium (Cd). To elucidate the biological activity of Shcrustin, we constructed a recombinant Shcrustin protein. Purified rShcrustin could bind to a variety of bacteria and inhibit the growth of different bacteria indicating that Shcrustin has inhibitory activity against gram-positive and gram-negative bacteria. In addition, the phagocytic rate of hemocytes toward bacteria decreased after the interference of Shcrustin expression by RNA interference, suggesting that Shcrustin may be involved in such a process. Therefore, we conclude that Shcrustin may be involved in the innate immunity of S. henanense by binding to bacteria and promoting hemolymph phagocytosis to clear invading pathogens. It is an important immune effector against pathogen infection. In the presence of Cd, it may alter the expression of Shcrustin and suppress its immune function.

MicroRNA transcriptome analysis of oriental river prawn Macrobrachium nipponense in responding to starvation stress

Food deprivation or fasting is an important environmental factor, and a regular occurrence in both natural aquatic habitats and artificial ponds. However, the potential immunoregulatory mechanisms underlying starvation stress in crustaceans remain unclear. MicroRNAs (miRNAs) are a new class of non-coding RNAs that can regulate various biological processes, such as stress and immune responses. In the present work, miRNAs related to starvation stress responses and immune properties were identified and characterised in oriental river prawn Macrobrachium nipponense using high-throughput sequencing and bioinformatics analyses. Twelve small RNA libraries from hepatopancreas tissue were sequenced across four fasting stages lasting 0, 7, 14 or 21 days. In total, 550 miRNAs were identified including 198 putative novel miRNAs and 352 conserved miRNAs belonging to 57 families. Moreover, compared with expression levels at 0 days, 27, 27 and 43 miRNAs were differentially expressed (DE-miRNAs) at 7, 14 and 21 days, respectively. Among these, four DE-miRNAs (ame-miR-190-5p, dme-miR-307a-3p, hme-miR-2788-3p and novel_68) were co-expressed at all three timepoints. Furthermore, 661 target genes regulated by these DE-miRNAs were identified, and associated functional annotations were derived by GO enrichment and KEGG pathway analyses, which showed that most DE-miRNAs were mainly participated in metabolic processes and immune responses. Furthermore, 26 host DE-miRNAs potentially participated in interactions with white spot syndrome virus (WSSV) were identified by predicting and analysing target genes from WSSV. The further WSSV challenge under starvation stress showed that dme-miR-307a-3p played a part in the antiviral responses against WSSV. Our results demonstrate that dme-miR-307a-3p may play vital regulatory roles in responding to starvation stress and WSSV infection. The findings contribute new insight into the molecular mechanisms associated with immune responses to environmental stress in crustaceans.

Clone, identification and functional characterization of a novel toll (Shtoll1) from the freshwater crab Sinopotamon henanense in response to cadmium exposure and Aeromonas hydrophila infection

Toll is essential in innate immune system which is important for defense against bacterial, fungal and viral infections in invertebrates. Our previous study showed that cadmium (Cd) could change the expression pattern of ShToll3 in the epithelium (gills and midgut from the freshwater crab Sinopotamon henanense) infected by Aeromonas hydrophila. To investigate the diverse innate immune roles of crustacean homolog Tolls, in this study, we cloned Shtoll1 from S. henanense. The full-length cDNA of Shtoll1 was 4746 bp, with an ORF of 3033 bp encoding a putative protein of 111 amino acids, a 5'-untranslated region of 255 bp and a 3'-untranslated region of 1713 bp. Phylogenetic analysis showed that ShToll1 was clustered into the group of DmToll1, DmToll 4 and DmToll 5. In addition, the tissue distribution results showed that Shtoll1 was expressed widely in different tissues, with the highest expression in heamocytes. Besides, Shtoll1 expressions were upregulated in heamocytes and hepatopancreas after A. hydrophila infection. At the same time, the increase of Shtoll1 expressions were examined in heamocytes in response to Cd exposure and A. hydrophila infection in combination. Through western blotting and immunohistochemical analysis, the ShToll1 expressions in heamocytes were increased in response to A. hydrophila and Cd independently as well as in combination. Moreover, the mRNA level of three antimicrobial peptides (AMPs) alf5, alf6, and c-lys, which possibly responded to Cd and A. hydrophila stimulation through Shtoll1, were analyzed. Thus, we conclude that Cd expand the susceptibility of ShToll1 to A. hydrophila infection in heamocytes. This suggest that ShToll1 may contribute to the innate immune defense of S. henanense against A. hydrophila and Cd in heamocytes.

Transcriptome-wide identification, functional characterization, and expression analysis of two novel invertebrate-type Toll-like receptors from disk abalone (Haliotis discus discus)

Toll-like receptors (TLRs) are well-known pattern recognition receptors that play key immunological roles in a diverse range of organisms. In this study, two novel invertebrate TLRs from disk abalone (designated as AbTLR-A and AbTLR-B) were identified and functionally characterized for the first time. AbTLR-A and AbTLR-B comprised the typical TLR domain architecture containing an extracellular leucine-rich repeat domain, transmembrane domain, and Toll/interleukin-1 receptor domain. Expressional analysis revealed that both TLRs were constitutively expressed at all the early embryonic stages of disk abalone analyzed, with the highest level of AbTLR-A found at the 16-cell stage and AbTLR-B at the trochophore stage. According to tissue distribution analysis, prominent mRNA expression of AbTLR-A and AbTLR-B was detected in the hemocytes and gills, respectively. AbTLR-A and AbTLR-B mRNAs were significantly up-regulated in response to Gram-negative Vibrio parahemolyticus, Gram-positive Listeria monocytogenes, and viral hemorrhagic septicemia virus injections in abalone hemocytes and gills. Overexpression of AbTLR-A and AbTLR-B in HEK293T cells directly activated nuclear factor-κB (NF-κB) and activator protein-1 (AP-1) responsive reporters. Neither TLRs showed a high response to pathogen-associated molecular patterns in vitro. Co-expression of AbTLR-A and AbTLR-B with AbMyD88-2 and AbMyD88-X activated NF-κB-responsive reporters in a synergetic manner. These findings demonstrate the involvement of AbTLR-A and AbTLR-B in abalone innate immunity.

SpToll1 and SpToll2 modulate the expression of antimicrobial peptides in Scylla paramamosain

Tolls and Toll-like receptors (TLRs) were the first pattern recognition receptors (PRRs) identified to play key roles in host innate immunity. However, relatively little is known about other types of Toll-like receptors in Scylla paramamosain, although a Toll-like receptor (SpToll1) has recently been cloned. In this study, we cloned and characterized another novel Toll-like receptor 2 (SpToll2) from S. paramamosain. The full-length cDNA of SpToll2 is 3391 bp with a 2646 bp open reading frame (ORF) encoding a putative protein of 881 amino acids, and predicted to contain six extracellular leucine-rich repeat (LRR) domains, a transmembrane domain and an intracellular Toll/IL-1 receptor (TIR) domain. Phylogenetic analysis revealed that SpToll2 clustered with Drosophila Toll1, and shared high homology with PtToll4. Real-time qPCR analysis showed that SpToll2 was widely expressed in all tissues tested, with the highest level found in hemocytes and hepatopancreas while the lowest in heart and muscle. The transcript levels of both SpToll1 and SpToll2 in mud crabs hemocytes was induced following challenge with Vibrio parahaemolyticus, Staphylococcus aureus, Polyinosinic: polycytidylic acid (Poly I:C) and white spot syndrome virus (WSSV). In addition, recombinant SpToll1-LRR and SpToll2-LRR proteins could bind to V. parahaemolyticus, S. aureus, Escherichia coli, and Beta Streptococcus. In order to study the signaling pathway of AMPs' expression in mud crab, RNA interference were used to test the expression of SpAMPs after the challenges with V. parahaemolyticus or S. aureus. The data suggested that SpToll1and SpToll2 could regulate the transcripts of several AMPs and four immune related mediators (SpMyD88, SpTube, SpPelle and SpTRAF6) at different scale. While silencing of SpToll1 post pathogens challenge attenuated the expression of SpHistin, SpALF1 and SpALF5 in mud crab's hemocytes, depletion of SpToll2 post pathogens challenge inhibited the expression of SpALF1-6, SpGRP, SpArasin and SpHyastastin. Furthermore, the results of overexpression assay also showed SpToll1 and SpToll2 could enhance the promoter activities of SpALFs in mud crab. Taken together, these results indicated that SpToll1 and SpToll2 might play important roles in host defense against pathogen invasions in S. paramamosain.