Two relish isoforms produced by alternative splicing participate in the regulation of antimicrobial peptides expression in Procambarus clarkii intestine

The first report of a C-type lectin contains a CLIP domain involved in antibacterial defense in Macrobrachium nipponense

We identified a novel C-type lectin (CTL) from Macrobrachium nipponense, designated as Mn-clip-Lec. It consists of 1315 bp with an open reading frame of 1098 bp, encoding a polypeptide of 365 amino acids. Mn-clip-Lec contains 6 exons and 5 introns. Mn-clip-Lec possessed a CLIP domain at the N-terminal and two carbohydrate recognition domains at the C-terminal. Interaction between Mn-clip-Lec and MnLec was found by Yeast two-hybrid analysis. The expressions of Mn-clip-Lec, MnLec, prophenoloxidase (proPO)-activating system-associated genes (MnPPAF, MnPPAE, and MnPO), and antimicrobial peptides (AMPs) (MnALF and MnCRU) were up-regulated after the challenge with Staphylococcus aureus. RNA interference (RNAi)-mediated suppression of the Mn-clip-Lec and MnLec genes in S. aureus-challenged prawns reduced the transcripts of MnPPAF, MnPPAE, MnPO, MnALF and MnCRU. Knockdown of Mn-clip-Lec and MnLec resulted in decrease in PO activity in M. nipponense infected with S. aureus. The recombinant Mn-clip-Lec (rMn-clip-Lec) protein bound all tested bacteria and agglutinated S. aureus. A sugar-binding assay revealed that rMn-clip-Lec could bind to LPS or PGN. rMn-clip-Lec accelerated the clearance of S. aureus in vivo. Our findings suggest that Mn-clip-Lec and its interacting MnLec play important roles in the induction of the proPO system and AMPs expression in M. nipponense during bacterial infection.

Immune function of a C-type lectin with long tandem repeats and abundant threonine in the ridgetail white prawn Exopalaemon carinicauda

C-type lectins (CTLs) are an important class of pattern recognition receptors (PRRs) that exhibit structural and functional diversity in invertebrates. Repetitive DNA sequences are ubiquitous in eukaryotic genomes, representing distinct modes of genome evolution and promoting new gene generation. Our study revealed a new CTL that is composed of two long tandem repeats, abundant threonine, and one carbohydrate recognition domain (CRD) in Exopalaemon carinicauda and has been designated EcTR-CTL. The full-length cDNA of EcTR-CTL was 1242 bp long and had an open reading frame (ORF) of 999 bp that encoded a protein of 332 amino acids. The genome structure of EcTR-CTL contains 4 exons and 3 introns. The length of each repeat unit in EcTR-CTL was 198 bp, which is different from the short tandem repeats reported previously in prawns and crayfish. EcTR-CTL was abundantly expressed in the intestine and hemocytes. After Vibrio parahaemolyticus and white spot syndrome virus (WSSV) challenge, the expression level of EcTR-CTL in the intestine was upregulated. Knockdown of EcTR-CTL downregulated the expression of anti-lipopolysaccharide factor, crustin, and lysozyme during Vibrio infection. The recombinant CRD of EcTR-CTL (rCRD) could bind to bacteria, lipopolysaccharides, and peptidoglycans. Additionally, rCRD can directly bind to WSSV. These findings indicate that 1) CTLs with tandem repeats may be ubiquitous in crustaceans, 2) EcTR-CTL may act as a PRR to participate in the innate immune defense against bacteria via nonself-recognition and antimicrobial peptide regulation, and 3) EcTR-CTL may play a positive or negative role in the process of WSSV infection by capturing virions.

A pattern recognition receptor interleukin-1 receptor is involved in reproductive immunity in Macrobrachium nipponense ovary

The family of TIR domain-containing receptors includes numerous proteins involved in innate immunity. In this study, a member of this family was characterized from the ovary of the oriental river prawn Macrobrachium nipponense and identified as interleukin-1 receptor (MnIL-1R). Meanwhile, to elucidate the conservation of IL-1R, its orthologous were identified in several crustacean species as well. In addition, the expression pattern of MnIL-1R in various adult tissues and post different pathogen-associated molecular patterns (PAMPs) challenge in ovary was analyzed with qRT-PCR technology. Finally, the roles of MnIL-1R in the ovary were analyzed by RNAi technology. The main results are as follows: (1) MnIL-1R comprises a 1785 bp ORF encoding 594 amino acids and is structurally composed of five domains: a signal peptide, two immunoglobulin (IG) domains, a transmembrane region, and a TIR-2 domain; (2) the TIR domain showed a high conservation among analyzed crustacean species; (3) MnIL-1R is widely detected in all tested tissues including ovary; (4) MnIL-1R showed a positive response to challenges with LPS, PGN, and polyI:C in the ovary; (5) its IG domain showed strong binding ability to LPS and PGN, confirming its role as a pattern recognition receptor; (6) the expression patterns of several members of the Toll signaling pathway (Myd88, TRAF-6, Dorsal, and Relish) was similar to that of MnIL-1R after challenges with LPS, PGN, and polyI:C in the ovary; (7) the silencing of MnIL-1R resulted in down-regulation of theses gene' (Myd88, TRAF-6, Dorsal, and Relish) expression level in the ovary. These results suggest that MnIL-1R can activate the Toll signaling pathway in the ovary by directly recognizing LPS and PGN through its IG domain, thereby contributing to the immune response in the ovary of M. nipponense.

Comparative Transcriptome Analysis of the Hepatopancreas from Macrobrachium rosenbergii Exposed to the Heavy Metal Copper

The contamination of aquatic ecosystems by the heavy metal copper (Cu) is an important environmental issue and poses significant risks to the physiological functions of aquatic organisms. Macrobrachium rosenbergii is one of the most important freshwater-cultured prawns in the world. The hepatopancreas of crustaceans is a key organ for immune defense, heavy metal accumulation, and detoxification, playing a pivotal role in toxicological research. However, research on the molecular response of the hepatopancreas in M. rosenbergii to Cu exposure is still lacking. In this study, the transcriptomic response in the hepatopancreas of M. rosenbergii was studied after Cu exposure for 3 and 48 h. Compared with the control group, 11,164 (7288 up-regulated and 3876 down-regulated genes) and 10,937 (6630 up-regulated and 4307 down-regulated genes) differentially expressed genes (DEGs) were identified after 3 and 48 h exposure, respectively. Most of these DEGs were up-regulated, implying that gene expressions were largely induced by Cu. Functional enrichment analysis of these DEGs revealed that immunity, copper homeostasis, detoxification, DNA damage repair, and apoptosis were differentially regulated by Cu. Seven genes involved in immunity, detoxification, and metabolism were selected for validation by qRT-PCR, and the results confirmed the reliability of RNA-Seq. All these findings suggest that M. rosenbergii attempts to resist the toxicity of Cu by up-regulating the expression of genes related to immunity, metabolism, and detoxification. However, with the excessive accumulation of reactive oxygen species (ROS), the antioxidant enzyme system was destroyed. As a result, DNA damage repair and the cellular stress response were inhibited, thereby exacerbating cell damage. In order to maintain the normal function of the hepatopancreas, M. rosenbergii removes damaged cells by activating the apoptosis mechanism. Our study not only facilitates an understanding of the molecular response mechanisms of M. rosenbergii underlying Cu toxicity effects but also helps us to identify potential biomarkers associated with the stress response in other crustaceans.

Alternative Splicing Reveals Acute Stress Response of Litopenaeus vannamei at High Alkalinity

Alkalinity is regarded as one of the primary stressors for aquatic animals in saline-alkaline water. Alternative splicing (AS) can significantly increase the diversity of transcripts and play key roles in stress response; however, the studies on AS under alkalinity stress of crustaceans are still limited. In the present study, we devoted ourselves to the study of AS under acute alkalinity stress at control (50 mg/L) and treatment groups (350 mg/L) by RNA-seq in pacific white shrimp (Litopenaeus vannamei). We identified a total of 10,556 AS events from 4865 genes and 619 differential AS (DAS) events from 519 DAS genes in pacific white shrimp. Functional annotation showed that the DAS genes primarily involved in spliceosome. Five splicing factors (SFs), U2AF1, PUF60, CHERP, SR140 and SRSF2 were significantly up-regulated and promoted AS. Furthermore, alkalinity activated the Leukocyte transendothelial migration, mTOR signaling pathway and AMPK signaling pathway, which regulated MAPK1, EIF3B and IGFP-RP1 associated with these pathways. We also studied three SFs (HSFP1, SRSF2 and NHE-RF1), which underwent AS to form different transcript isoforms. The above results demonstrated that AS was a regulatory mechanism in pacific white shrimp in response to acute alkalinity stress. SFs played vital roles in AS of pacific white shrimp, such as HSFP1, SRSF2 and NHE-RF1. DAS genes were significantly modified in immunity of pacific white shrimp to cope with alkalinity stress. This is the first study on the response of AS to acute alkalinity stress, which provided scientific basis for AS mechanism of crustaceans response to alkalinity stress.

In-depth transcriptomic analysis of Anopheles gambiae hemocytes uncovers novel genes and the oenocytoid developmental lineage

BACKGROUND

Hemocytes are immune cells that patrol the mosquito hemocoel and mediate critical cellular defense responses against pathogens. However, despite their importance, a comprehensive transcriptome of these cells was lacking because they constitute a very small fraction of the total cells in the insect, limiting the study of hemocyte differentiation and immune function.

RESULTS

In this study, an in-depth hemocyte transcriptome was built by extensive bulk RNA sequencing and assembly of hemocyte RNAs from adult A. gambiae female mosquitoes, based on approximately 2.4 billion short Illumina and about 9.4 million long PacBio high-quality reads that mapped to the A. gambiae PEST genome (P4.14 version). A total of 34,939 transcripts were annotated including 4,020 transcripts from novel genes and 20,008 novel isoforms that result from extensive differential splicing of transcripts from previously annotated genes. Most hemocyte transcripts identified (89.8%) are protein-coding while 10.2% are non-coding RNAs. The number of transcripts identified in the novel hemocyte transcriptome is twice the number in the current annotation of the A. gambiae genome (P4.14 version). Furthermore, we were able to refine the analysis of a previously published single-cell transcriptome (scRNAseq) data set by using the novel hemocyte transcriptome as a reference to re-define the hemocyte clusters and determine the path of hemocyte differentiation. Unsupervised pseudo-temporal ordering using the Tools for Single Cell Analysis software uncovered a novel putative prohemocyte precursor cell type that gives rise to prohemocytes. Pseudo-temporal ordering with the Monocle 3 software, which analyses changes in gene expression during dynamic biological processes, determined that oenocytoids derive from prohemocytes, a cell population that also gives rise to the granulocyte lineage.

CONCLUSION

A high number of mRNA splice variants are expressed in hemocytes, and they may account for the plasticity required to mount efficient responses to many different pathogens. This study highlights the importance of a comprehensive set of reference transcripts to perform robust single-cell transcriptomic data analysis of cells present in low abundance. The detailed annotation of the hemocyte transcriptome will uncover new facets of hemocyte development and function in adult dipterans and is a valuable community resource for future studies on mosquito cellular immunity.

Alternative Splicing, An Overlooked Defense Frontier of Plants with Respect to Bacterial Infection

Disease represents a major problem in sustainable agricultural development. Plants interact closely with various microorganisms during their development and in response to the prevailing environment. In particular, pathogenic microorganisms can cause plant diseases, affecting the fertility, yield, and longevity of plants. During the long coevolution of plants and their pathogens, plants have evolved both molecular pattern-triggered immunity (PTI) and effector-triggered immunity (ETI) signaling networks in order to regulate host cells in response to pathogen infestation. Additionally, in the postgenomic era, alternative splicing (AS) has become uncovered as one of the major drivers of proteome diversity, and abnormal RNA splicing is closely associated with bacterial infections. Currently, the complexity of host-bacteria interactions is a much studied area of research that has shown steady progress over the past decade. Although the development of high-throughput sequencing technologies and their application in transcriptomes have revolutionized our understanding of AS, many mechanisms related to host-bacteria interactions remain still unclear. To this end, this review summarizes the changes observed in AS during host-bacteria interactions and outlines potential therapeutics for bacterial diseases based on existing studies. In doing so, we hope to provide guidelines for plant disease management in agriculture.

The Responses of Alternative Splicing during Heat Stress in the Pacific White Shrimp Litopenaeus vannamei

Heat tolerance is increasingly becoming a crucial trait for aquaculture species in the face of rapidly changing climate conditions. Alternative splicing (AS) is a vital mechanism within cells that modulates gene abundance and functional diversity, enabling organisms to effectively respond to diverse stressful conditions, including thermal stress. However, it is still uncertain whether AS contributes to heat tolerance in shrimp. In this study, we conducted an extensive transcriptome analysis on the Pacific white shrimp, Litopenaeus vannamei, revealing a total of 1267, 987, and 130 differential AS events (DAS) in the gill, hepatopancreas, and muscle, respectively, following exposure to heat stress. Among all of the DAS events, exon skipping (ES) was the predominant form of splicing modification observed. Interestingly, a minor portion of DAS genes exhibited overlap across the three tissues, implying that heat stress exerts unique effects on various tissue types. Moreover, the functional enrichment analysis demonstrated that commonly identified DAS genes were primarily associated with the "spliceosome" pathway, indicating that the AS of splicing-related genes played a crucial role in the response to heat stress. Our findings also revealed that heat stress tended to induce longer mRNA isoforms through differential alternative 3' splice site (A3SS) events. Notably, A3SS events exhibited the highest proportion of maintained open reading frames (ORFs) under heat stress. Interestingly, we observed a limited overlap between the genes exhibiting DAS and those showing differential gene expression (DEG), indicating that AS may function as a distinct regulatory mechanism independent of transcriptional regulation in response to heat stress. This is the first comprehensive study on AS in crustacea species under heat stress, which broadens our understanding of the regulatory mechanisms governing the crustaceans' response to environmental stress, providing valuable insights for the aquaculture breeding of shrimp and other aquatic animals.

Redclaw crayfish (Cherax quadricarinatus) responds to Vibrio parahaemolyticus infection by activating toll and immune deficiency signaling pathways and transcription of associated immune response genes

In invertebrates, several genes controlled by the Toll and immunodeficiency (IMD) signaling cascade are altered during microbial infection. However, little is known about the expression patterns of innate immune response genes in red-clawed crayfish (Cherax quadricarinatus). In the present study, the transcription of five genes was assessed in C. quadricarinatus challenged with Vibrio parahaemolyticus (V. parahaemolyticus). The expression of Relish, Toll-like receptor (TLR), tumor necrosis factor receptor-related factor 6 (TRAF6), Akirin, and IMD in different tissues and at different time points after infection were assessed. In addition, the Relish gene was amplified, the protein conformation of the Relish gene was predicted, and gene expression changes associated with antimicrobial peptide production in C. quadricarinatus were analyzed using RNA interference (RNAi). During V. parahaemolyticus infection, the transcripts of the above five genes were significantly increased in the hepatopancreas of C. quadricarinatus (P < 0.05). In contrast, TLR was significantly downregulated in muscle tissue at the initial stage of infection (P < 0.05); TRAF6 and IMD were significantly down-regulated throughout infection (P < 0.05); Akirin transcripts had the lowest abundance at 24 h post-infection; Relish, IMD and Akirin genes were significantly up-regulated in gill tissue at the early stage of infection (P < 0.05); only TRAF6 was significantly up-regulated at 6, 24 and 48 h after infection. The Relish gene of C. quadricarinatus is closely related to the Exopalaemon carinicauda. When the Relish gene was knocked down by RNAi, the V. parahaemolyticus challenge showed that the mortality rate of the RANi group was significantly higher than that of the NC group; pathological sections showed that the hepatopancreatic tissue damage was the most severe 12 h after the interference; and the interference significantly inhibited IRF4, NF-κB, ALF, laccase, SOD1, and lectin genes. Therefore, it can be hypothesized that the Toll and IMD pathways are activated in C. quadricarinatus in response to bacterial infection and that genes associated with these pathways are differentially transcribed in different tissues. This study provides insights into the Toll and IMD signaling pathways and the spatiotemporal expression of key genes regulating bacterial infection resistance in C. quadricarinatus.

Characterization of four spliced isoforms of a transmembrane C-type lectin from Procambarus clarkii and their function in facilitating WSSV infection

C-type lectin (CTL) is an important pattern recognition receptor that play vital functions in the innate immunity. Many soluble CTLs in crustacean participate in the inhibition or promotion of white spot syndrome virus (WSSV) infection. However, whether transmembrane CTLs participate in WSSV infection in crustacean remains unknown. In the present study, four spliced isoforms of a transmembrane CTL (designated as PcTlec) from Procambarus clarkii were identified for the first time. The genome structure of PcTlec contains eight exons, six known introns, and one unknown intron. PcTlec-isoform1 is produced by intron retention, whereas PcTlec-isoform3 and PcTlec-isoform4 are produced by exon skipping. All of them contain the transmembrane domain and characteristic carbohydrate recognition domain (CRD). Four PcTlec isoforms were mainly expressed in the hepatopancreas, stomach, and intestine. After WSSV challenge, the expression levels of PcTlec-isoform1-4 in the intestine were upregulated. The knockdown of the region shared by four PcTlec isoforms evidently decreased the expression of WSSV envelope protein VP28 and the copies of viral particles. A recombinant protein (rPcTlec-CRD) containing the CRD that was shared by four PcTlec isoforms was acquired by procaryotic expression system. The injection of purified rPcTlec-CRD protein evidently increased the VP28 expression and WSSV copies during viral infection. Moreover, rPcTlec-CRD could directly bind to WSSV and interact with VP28 protein. These findings indicate that new-found transmembrane CTL isoforms in P. clarkii may act as viral receptors that facilitate WSSV infection. This study contributes to the recognition and understanding of the functions of transmembrane CTLs in crustacean in the infection of host by WSSV.

Characterization and functional analysis of a clip domain serine protease (MncSP) and its alternative transcript (MncSP-isoform) from Macrobrachium nipponense

Clip domain serine protease (cSPs) play an important role in the innate immune defense of crustaceans. In this study, a clip domain serine protease (MncSP) and its alternative transcript (MncSP-isoform) were identified from Macrobrachium nipponense. The full-length cDNA sequences of MncSP and MncSP-isoform were 2447 and 2351 bp with open reading frames comprising 1497 and 1401 bp nucleotides and encoding 498 and 466 amino acids, respectively. The genome of MncSP had 10 exons and 9 introns. MncSP contained all 10 exons, whereas MncSP-isoform lacked the second exon. MncSP and MncSP-isoform contained a signal peptide, a clip domain, and a Tryp_SPc domain. Phylogenetic tree analysis showed that MncSP and MncSP-isoform clustered with cSPs from Palaemonidae. MncSP and MncSP-isoform were widely distributed in hemocytes, heart, hepatopancreas, gills, stomach, and intestine. The expression profiles of MncSP and MncSP-isoform in the hemocytes of M. nipponense changed after simulation by Vibrio parahaemolyticus or Staphylococcus aureus. The RNAi of MncSP could inhibit the expression of antimicrobial peptides (AMPs), including crustins and anti-lipopolysaccharide factors. Phenoloxidase activity was also down-regulated in MncSP-silenced prawns. This study indicated that MncSP participated in the synthesis of AMPs and the activation of prophenoloxidase.

The potential of antimicrobial peptides isolated from freshwater crayfish species in new drug development: A review

The much-publicised increased resistance of pathogenic bacteria to conventional antibiotics has focused research effort on the characterization of new antimicrobial drugs. In this context, antimicrobial peptides (AMPs) extracted from animals are considered a promising alternative to conventional antibiotics. In recent years, freshwater crayfish species have emerged as an important source of bioactive compounds. In fact, these invertebrates rely on an innate immune system based on cellular responses and on the production of important effectors in the haemolymph, such as AMPs, which are produced and stored in granules in haemocytes and released after stimulation. These effectors are active against both Gram-positive and Gram-negative bacteria. In this review, we summarise the recent progress on AMPs isolated from the several species of freshwater crayfish and their prospects for future pharmaceutical applications to combat infectious agents.

Identification of four Spätzle genes (MnSpz1, MnSpz2, MnSpz2-isoform, and MnSpz3) and their roles in the innate immunity of Macrobrachium nipponense

Spätzle, an extracellular ligand of the Toll receptor, is involved in the innate immunity of crustaceans. In this study, four Spätzle genes were cloned from Macrobrachium nipponense and designed as MnSpz1, MnSpz2, MnSpz2-isoform, and MnSpz3. The coding region of the four Spätzle genes all contained one intron and two exons, and they were predicted to be produced by gene duplication based on sequence similarities and phylogenetic tree. The predicted MnSpz1, MnSpz2, and MnSpz3 proteins all contained a signal peptide and a Spätzle domain. No signal peptide but a Spätzle domain existed in MnSpz2-isoform because of frameshift mutation caused by 50 bp nucleotide deletion compared with MnSpz2. Quantitative real-time polymerase chain reaction (RT-qPCR) analysis showed that MnSpz1, MnSpz2, and MnSpz3 were expressed in all the detected tissues of M. nipponense, and MnSpz2 was found to be the major isoform in the heart, gills, stomach, and intestine. After stimulation by Vibrio parahaemolyticus, Staphylococcus aureus, or White spot syndrome virus (WSSV), the expression levels of MnSpz1, MnSpz2, and MnSpz3 changed. Given the high similarities among MnSpz1-3, RNA interference (RNAi) using dsRNA of MnSpz1 inhibited the expression of the three Spätzle genes (MnSpz1, MnSpz2 and MnSpz3). Silencing of MnSpz1-3 down-regulated the expression levels of nine antimicrobial peptide (AMP) genes in M. nipponense. After Knockdown of MnSpzs, the number of V. parahaemolyticus, S. aureus and WSSV copies in M. nipponense increased significantly in vivo. Our results suggest that Spätzles are involved in the innate immunity of M. nipponense. The expansion of MnSpz genes through gene duplication is beneficial to enhance the innate immune defense ability of M. nipponense.

Interleukin enhancer binding factor 2 (IEBF 2) was involved in the regulation of the antibacterial immune reactions in fresh water crayfish, Procambarus clarkii

Although interleukin and interleukin analogues which play important immunomodulatory roles in mammals have not yet been reported in invertebrates, interleukin enhancer binding factor (IEBF) which acts as a transcription factor has been recently studied in several crustaceans and it may be involved in innate immune defence against pathogens. In this study, an IEBF 2 homologue was identified in the fresh water crayfish, Procambarus clarkii. The significantly changed expression levels of Pc-iebf 2 after bacterial challenge revealed the possibility of its participation in defence against bacterial infection. The results of an RNAi assay showed that the crayfish survival rate was obviously decreased after dsIEBF 2 injection, compared with the control groups. And S. aureus proliferation was obviously enhanced at 24 and 48 h post bacterial injection, when Pc-iebf 2 was knocked down. The possible molecular mechanisms for the innate immune regulation functions of Pc-IEBF 2 were also investigated. We speculated that Pc-IEBF 2 plays an important role in defending against bacterial infection in crayfish. It could regulate some innate immune responses by affecting the Toll signalling pathway, melanisation, and cell apoptosis.

Identification of two carcinin isoforms (MnCarc1 and MnCarc2) and their function in the antimicrobial immunity of Macrobrachium nipponense

Carcinin, a member of the crustin family, plays important roles in crustacean innate immunity. In this study, we identified two carcinin isoforms (MnCarc1 and MnCarc2) produced by alternative splicing from Macrobrachium nipponense. The full length of MnCarc1 and MnCarc2 cDNA are 1554 and 1495 bp with 687 and 609 bp open reading frame-encoding proteins that contain 228 and 202 amino acids, respectively. The genome of carcinin has nine exons and eight introns. MnCarc1 transcript contains all nine exons, whereas MnCarc2 only contains eight exons and lacks exon 4. MnCarc1 and MnCarc2 proteins contain a signal peptide, cysteine-rich regions, and a whey acidic protein domain. The phylogenetic tree shows that MnCarc1 and MnCarc2 are not grouped with other crustins and carcinins. MnCarc1 and MnCarc2 form a subgroup. MnCarc1 and MnCarc2 are widely distributed in various tissues. The expression of MnCarc1 and MnCarc2 were evidently upregulated at multiple time points in hemocytes and the intestine of M. nipponense after white spot syndrome virus, Vibrio parahaemolyticus, and Staphylococcus aureus challenges. Further studies showed that knockdown of MnDorsal or MnStat transcription factor could remarkably inhibit the upregulated expression of MnCarc1 and MnCarc2 caused by viral or bacterial challenges. In addition, recombinant MnCarc1 and MnCarc2 proteins could bind to various bacteria and polysaccharides and inhibit the growth of S. aureus and V. parahaemolyticus in vitro. This study indicated that carcinins from M. nipponense were involved in prawns innate immunity.

Characterization and antimicrobial evaluation of a new Spgly-AMP, glycine-rich antimicrobial peptide from the mud crab Scylla paramamosain

Antimicrobial peptide (AMP) is a crucial component of the innate immune system in crustaceans. In mud crab, Scylla paramamosain, a commercially important species, a glycine-rich antimicrobial peptide (Spgly-AMP) gene was newly identified and putatively encoded a 26aa signal peptide and 37aa mature peptide. To understand the function of Spgly-AMP, the expression profile of Spgly-amp gene was characterized, which showed Spgly-amp was expressed widely in most tissues of adult crabs with the highest expression level in hemocytes. After Vibrio parahaemolyticus, PGN, or Poly I:C stimulations, the expression level of Spgly-amp was significantly up-regulated in the hemocytes. In antimicrobial assays, chemically synthesized Spgly-AMP peptides exhibited strong antibacterial activities against both Gram-positive and Gram-negative bacteria and high thermal stability after high-temperature heating. These findings in the present study verified the importance of the Spgly-AMP in defense of pathogenic bacteria infection in the mud crab and provided a promising candidate of antimicrobial agents in the crab aquaculture.

Taiman negatively regulates the expression of antimicrobial peptides by promoting the transcription of cactus in Macrobrachium nipponense

In insects, Taiman (Tai) participates in the juvenile hormone, 20-hydroxyecdysone, insulin, and Hippo signaling pathways. However, the role of Tai in crustacean innate immunity is less known. In this study, four Tai isoforms (MnTai-A, MnTai-B, MnTai-C, and MnTai-D) produced by alternative splicing were identified from Macrobrachium nipponense. The obtained genome sequences indicated that MnTai DNA has more than 20 exons and 19 introns. The second to last (-exon2) and the third to last (-exon3) exons can be alternatively spliced. The loss of -exon2 or -exon3 produces MnTai-B or MnTai-C, respectively. Both exons are absent in MnTai-D. The full-length cDNA of MnTai-A (including all exons) was 6894 bp with an open reading frame of 4998 bp that encoded a protein of 1665 amino acids. MnTaiA contains the conservative structure of the Tai family and clustered with nuclear receptor coactivator from shrimp. All these four isoforms were widely distributed in a variety of tissues with the highest expression level in the hepatopancreas except MnTaiC. The transcriptional levels of total Tai genes (designated as MnTaiT) in the hepatopancreas and gills were regulated by bacterial or viral challenge. Knockdown of MnTaiT increased the expression of anti-microbial peptides (AMPs) during Vibrio parahaemolyticus infection. Further study indicated that the negative regulation of AMP gene expression by prawn Tai was mediated through its positive regulation of cactus. Our research provides valuable information that prawn Tai isoforms are involved in innate immunity.