Integrated analysis of mRNA-seq in the haemocytes of Eriocheir sinensis in response to Spiroplasma eriocheiris infection

A time-dependent interactive effect of nitrite and ammonia on inflammatory and immune response in the head kidney of silver carp (Hypophthalmichthys molitrix)

Nitrite and ammonia stress frequently have harmful effects on aquatic animals. However, the effect of ammonia combined with nitrite on immunity is unclear. Aimed to determine their interactive effect on head kidney, silver carp were exposed to ammonia (15 mg/L), nitrite (10 mg/L), or ammonia+nitrite (15 mg/L + 10 mg/L), and control conditions for 48 h. The results showed that exposure to nitrite and ammonia caused loss of cytoplasm and vacuolar degeneration of cells in head kidney. Following exposure to nitrite and ammonia, tumor necrosis factor alpha (TNF-α) and interleukin-1β (IL-1β) levels decreased significantly, while immunoglobulin M (IgM) and complement 3 (C3) levels increased significantly (P < 0.05). Additionally, TNF-α and C3 were significantly affected synergistically by 24 h of exposure to ammonia+nitrite, while significantly antagonistic effect on IL-1β and C3 was observed after 48 h of exposure. After 48 h of exposure, differently expressed genes (DEGs) induced by ammonia, nitrite, and their combination were mainly assigned to molecular function and biological process, and complement and coagulation cascade pathway was enriched with the highest number of immunity-associated DEGs. Integrated biomarker response (IBR) in nitrite group was higher than that in ammonia group, and the combination of ammonia and nitrite increased and decreased the IBR induced by ammonia and nitrite after 24 and 48 h of exposure, respectively. In conclusion, the toxicities of ammonia and nitrite toward head kidney displayed inflammatory suppression and immune activation, and their had synergistic and antagonistic effects on head kidney at 24 h and 48 h, respectively.

Impacts of nanopolystyrene and/or phoxim exposure at environmentally relevant concentrations on the intestinal histopathology, intestinal microbiota, and metabolome in Eriocheir sinensis

Nanopolystyrene (NP) pollution in aquatic environments has become an increasing concern. Phoxim (PHO), one of the major organophosphorus pesticides, has also been detected in aquatic environments, posing serious health risks to crustaceans. This study aimed to assess the detrimental effects of NP and/or PHO exposure at environmentally relevant concentrations on the intestinal histopathology, intestinal microbiota, and metabolome of adult crabs (Eriocheir sinensis) for 21 days. Our study revealed significant histopathological abnormalities in the intestines. In all the exposure groups, there was a discovery of vacuolar degeneration occurring in epithelial cells. Additionally, the peritrophic membrane exhibited thinning after NP or PHO single exposure, while thickening was observed after co-exposure. Exposure to NP and/or PHO disrupted the intestinal microbiota homeostasis, as evidenced by the proliferation of pathogenic bacteria and suppression of beneficial bacteria. Notably, PHO exposure resulted in increased abundance of pathogenic bacteria (Spiroplasma and Arcobacter) and decreased abundance of beneficial bacteria (Bacteroides). Analysis of the metabolome revealed that exposure to NP and/or PHO led to alterations in the metabolic profile as well as several critical pathways. Among these, the upregulation of arachidonic acid metabolism, ABC transporters, and biosynthesis of amino acids was observed in both NP single exposure and co-exposure, while PHO single exposure downregulated these pathways. Additionally, NP and/or PHO exposure downregulated neuroactive ligand-receptor interaction. Spearman correlation analysis revealed that the significant reduction of some differentially expressed metabolites (DEMs) was potentially regulated by the low-abundance bacterial genera following exposure to NP and/or PHO. And these DEMs have a role in anti-inflammatory or antioxidant properties. Collectively, our results offer novel perspectives on the intestinal toxicity of crustaceans by NP and/or PHO at environmentally relevant concentrations.

Combined effects of low pH stress and bacterial infection on the transcriptional changes of hemocytes in Chinese mitten crab Eriocheir sinensis

Water pH is a critical environmental factor for aquaculture. Acidification is a pressing environmental issue that poses significant threats to the aquaculture industry. Since the outbreaks of disease generally accompany with environmental stress, comparative transcriptome analyses were performed to investigate the combined effects of low pH stress and bacterial infection on the transcriptional changes of hemocytes in the economically important crab Eriocheir sinensis. The results revealed that the immune deficiency (IMD) pathway and prophenoloxidase (proPO) system was activated to defense against Vibro parahaemolyticus even when crabs were subjected to low pH stress, whereas low pH stress resulted in the disorder of Toll-like receptor (TLR) pathway upon V. parahaemolyticus infection. Moreover, low pH stress might weaken crabs' defense against V. parahaemolyticus by inhibiting the up-regulation of crustin and suppressing the expression of lysozyme, and disturb the maintaining of protein homeostasis through the transcriptional decrement of a batch of heat shock proteins (HSPs). It is worth noting that both V. parahaemolyticus infection and low pH stress might suppress the energy metabolism in the hemocytes via inhibiting the expression of critical enzymes, dihydrolipoyllysine-residue acetyltransferase component of pyruvate dehydrogenase complex and fumarase, in the tricarboxylic acid (TCA) cycle. This study provides novel understandings concerning the transcriptional changes of hemocyte in E. sinensis subjected to a combination of low pH stress and V. parahaemolyticus infection as well as contribute to optimize the management strategies for the prevention and control of diseases in E. sinensis farming.

Cellular and transcriptomic response to pathogenic and non-pathogenic Vibrio parahaemolyticus strains causing acute hepatopancreatic necrosis disease (AHPND) in Litopenaeus vannamei

The shrimp industry has historically been affected by viral and bacterial diseases. One of the most recent emerging diseases is Acute Hepatopancreatic Necrosis Disease (AHPND), which causes severe mortality. Despite its significance to sanitation and economics, little is known about the molecular response of shrimp to this disease. Here, we present the cellular and transcriptomic responses of Litopenaeus vannamei exposed to two Vibrio parahaemolyticus strains for 98 h, wherein one is non-pathogenic (VpN) and the other causes AHPND (VpP). Exposure to the VpN strain resulted in minor alterations in hepatopancreas morphology, including reductions in the size of R and B cells and detachments of small epithelial cells from 72 h onwards. On the other hand, exposure to the VpP strain is characterized by acute detachment of epithelial cells from the hepatopancreatic tubules and infiltration of hemocytes in the inter-tubular spaces. At the end of exposure, RNA-Seq analysis revealed functional enrichment in biological processes, such as the toll3 receptor signaling pathway, apoptotic processes, and production of molecular mediators involved in the inflammatory response of shrimp exposed to VpN treatment. The biological processes identified in the VpP treatment include superoxide anion metabolism, innate immune response, antimicrobial humoral response, and toll3 receptor signaling pathway. Furthermore, KEGG enrichment analysis revealed metabolic pathways associated with survival, cell adhesion, and reactive oxygen species, among others, for shrimp exposed to VpP. Our study proves the differential immune responses to two strains of V. parahaemolyticus, one pathogenic and the other nonpathogenic, enlarges our knowledge on the evolution of AHPND in L. vannamei, and uncovers unique perspectives on establishing genomic resources that may function as a groundwork for detecting probable molecular markers linked to the immune system in shrimp.

Toxic effects of nanopolystyrene and cadmium on the intestinal tract of the Chinese mitten crab (Eriocheir sinensis)

Nanopolystyrene (NP) and cadmium (Cd) are ubiquitous contaminants in aquatic systems. The present study aimed to investigate the toxic effects of exposure to ambient concentrations of NP and/or Cd on the intestinal tract of the Chinese mitten crab (Eriocheir sinensis). Exposure to NP and/or Cd induced oxidative stress, as evidenced by a significant increase in lipid peroxide content (LPO), total antioxidant capacity (T-AOC), and peroxidase activity (POD), and significant decreases in superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) activities in E. sinensis. In addition, exposure to NP and/or Cd imbalanced the homeostasis of the intestinal microbiota, as demonstrated by the significantly increased abundance of Spiroplasma. Transcriptomic and metabolomic analyses were performed to investigate the mechanisms underlying intestinal toxicity. Our results showed that ferroptosis, ABC transporters, phosphotransferase system, apoptosis, and leukocyte transendothelial migration were disturbed after exposure to NP and/or Cd. In particular, Cd exposure affected mucin type O-glycan biosynthesis, purine metabolism, and neuroactive ligand-receptor interaction. Intriguingly, co-exposure to NP and Cd might mitigate intestinal toxicity by decreasing oxidative stress and affecting these pathways. Taken together, our study clearly demonstrates that exposure to NP and/or Cd at environmentally relevant concentrations causes intestinal toxicity in E. sinensis.

Integrative omics analysis highlights the immunomodulatory effects of the parasitic dinoflagellate hhematodinium on crustacean hemocytes

Parasitic dinoflagellates in genus Hematodinium have caused substantial economic losses to multiple commercially valuable marine crustaceans around the world. Recent efforts to better understand the life cycle and biology of the parasite have improved our understanding of the disease ecology. However, studies on the host-parasite interaction, especially how Hematodinium parasites evade the host immune response are lacking. To address this shortfall, we used the comprehensive omics approaches (miRNA transcriptomics, iTRAQ-based proteomics) to get insights into the host-parasite interaction between hemocytes from Portunus trituberculatus and Hematodinium perezi in the present study. The parasitic dinoflagellate H. perezi remodeled the miRNome and proteome of hemocytes from challenged hosts, modulated the host immune response at both post-transcriptional and translational levels and caused post-transcriptional regulation to the host immune response. Multiple important cellular and humoral immune-related pathways (ex. Apoptosis, Endocytosis, ECM-receptor interaction, proPO activation pathway, Toll-like signaling pathway, Jak-STAT signaling pathway) were significantly affected by Hematodinium parasites. Through modulation of the host miRNome, the host immune responses of nodulation, proPO activation and antimicrobial peptides were significantly suppressed. Cellular homeostasis was imbalanced via post-transcriptional dysregulation of the phagosome and peroxisome pathways. Cellular structure and communication was seriously impacted by post-transcriptional downregulation of ECM-receptor interaction and focal adhesion pathways. In conclusion, H. perezi parasites could trigger striking changes in the miRNome and proteome of crustacean hemocytes, and this parasite exhibited multifaceted immunomodulatory effects and potential immune-suppressive mechanisms in crustacean hosts.

Signaling Pathways That Regulate the Crustacean Molting Gland

A pair of Y-organs (YOs) are the molting glands of decapod crustaceans. They synthesize and secrete steroid molting hormones (ecdysteroids) and their activity is controlled by external and internal signals. The YO transitions through four physiological states over the molt cycle, which are mediated by molt-inhibiting hormone (MIH; basal state), mechanistic Target of Rapamycin Complex 1 (mTORC1; activated state), Transforming Growth Factor-β (TGFβ)/Activin (committed state), and ecdysteroid (repressed state) signaling pathways. MIH, produced in the eyestalk X-organ/sinus gland complex, inhibits the synthesis of ecdysteroids. A model for MIH signaling is organized into a cAMP/Ca2+-dependent triggering phase and a nitric oxide/cGMP-dependent summation phase, which maintains the YO in the basal state during intermolt. A reduction in MIH release triggers YO activation, which requires mTORC1-dependent protein synthesis, followed by mTORC1-dependent gene expression. TGFβ/Activin signaling is required for YO commitment in mid-premolt. The YO transcriptome has 878 unique contigs assigned to 23 KEGG signaling pathways, 478 of which are differentially expressed over the molt cycle. Ninety-nine contigs encode G protein-coupled receptors (GPCRs), 65 of which bind a variety of neuropeptides and biogenic amines. Among these are putative receptors for MIH/crustacean hyperglycemic hormone neuropeptides, corazonin, relaxin, serotonin, octopamine, dopamine, allatostatins, Bursicon, ecdysis-triggering hormone (ETH), CCHamide, FMRFamide, and proctolin. Contigs encoding receptor tyrosine kinase insulin-like receptor, epidermal growth factor (EGF) receptor, and fibroblast growth factor (FGF) receptor and ligands EGF and FGF suggest that the YO is positively regulated by insulin-like peptides and growth factors. Future research should focus on the interactions of signaling pathways that integrate physiological status with environmental cues for molt control.

Full-length transcriptome and long non-coding RNA profiling of whiteleg shrimp Penaeus vannamei hemocytes in response to Spiroplasma eriocheiris infection

Spiroplasma eriocheiris (S. eriocheiris) infection causes a significant economic loss in Penaeus vannamei (P. vannamei) culture industry. However, the response of P. vannamei hemocytes to S. eriocheiris infection has not been extensively studied. In this study, we conducted full-length transcriptome and long non-coding RNA (lncRNA) analyses of P. vannamei hemocytes by a challenge test with S. eriocheiris. Following assembly and annotation, there were 8077 high-quality unigenes. A total of 1168 differentially expressed genes (DEGs) were obtained, including 792 up-regulated and 376 down-regulated genes by differential expression analysis. Gene ontology (GO) enrichment analysis showed that the up-regulated DEGs were mainly clustered into immune system process, defense response, cell cycle and organelle organization. On the other hand, the down-regulated DEGs included that genes that were mainly clustered into metabolic processes related to organic compounds, metabolic process and cellular metabolic process. Protein-protein interaction (PPI) network analysis of DEGs indicated that the pivotal gene interactions were connected to stress response, immune system process and cell cycle. The lncRNA analysis identified multiple lncRNAs, which were highly co-expressed with the immune-related genes, such as lncRNA transcript-12631 and transcript-12631, suggesting that lncRNAs may be involved in the regulation of immune defense in shrimp hemocytes. Additionally, 20 hub unigenes and putative lncRNAs related to immune system were validated by quantitative real-time PCR (qRT-PCR), validating the reliability of RNA-Seq. This study revealed a close connection between the immune and metabolic systems of S. eriocheiris infected P. vannamei.

Comparative transcriptomics reveals eyestalk ablation induced responses of the neuroendocrine-immune system in the Pacific white shrimp Litopenaeus vannamei

In decapod crustaceans, eyestalk ablation is widely used to expedite ovarian maturation and spawning because of the removal of a gonad inhibiting hormone produced by the X-organ sinus gland. However, eyestalk ablation also results in negative impacts on the immunocompetence of the eyestalk-ablated females. In the current study, we investigated the impact of eyestalk ablation on the transcriptomic responses of three major nervous organs of shrimp, including the eyestalk ganglion, brain and thoracic ganglion, using the Illumina Hiseq™ 4000 platform. A total of 48,249 unigenes with an average length of 1253 bp and a N50 value of 2482 bp were obtained. Following eyestalk ablation treatment, a total of 2,983, 6325 and 6575 unigenes were detected as differentially expressed (log₂Ratio >1 and FDR <0.05) from the eyestalk, brain and thoracic ganglia, respectively. Functional GO and KEGG analysis of these differential expression genes (DEGs) showed that these DEGs were associated with a wide variety of biological processes and pathways. The distribution of DEGs among three comparison groups was similar, and many DEGs were mapped to the phagosome pathway, indicating that eyestalk ablation triggers activation of the neuroendocrine-immune (NEI) system. Interestingly, several important pathways were uniquely enriched in the brain tissue, suggesting that the brain may play a crucial role in the NEI system in response to eyestalk ablation. This is the first report on the transcriptomic regulation of the nervous system in response to eyestalk ablation in L. vannamei. The genes and pathways identified in this study will help to elucidate the molecular mechanisms of neuroendocrine-immune responses to eyestalk ablation in penaeid shrimp.

Transcriptome-wide analysis of immune responses in Eriocheir sinensis hemocytes after challenge with different microbial derivatives

Knowledge about how Eriocheir sinensis interacts with microorganisms in its ambient environment is still lacking. Using RNA-Seq, we determined the most conserved genes and pathways compared with other animals and detected highly-induced immune genes in E. sinensis hemocytes post-in vivo challenge with different microbial derivatives. In total, 33.2 million high-quality reads were generated and assembled into 177,679 contigs. Completeness assessment and functional annotation were performed. Lipopolysaccharide, peptidoglycan, and β-1, 3-glucan stimulation induced 373, 173, and 108 differentially expressed (DE) transcripts, respectively. GO terms such as 'G-protein-coupled receptor binding', 'negative regulation of mitogen-activated protein kinase activity', and 'positive regulation of blood circulation' were enriched in the DE transcripts. Quantitative real-time PCR validated the data for selected genes. Our data contribute to understanding the immune defense mechanism in E. sinensis and the development of the innate immune system, thereby providing insights into disease control and prevention in aquaculture.

The Single-molecule long-read sequencing of Scylla paramamosain

Scylla paramamosain is an important aquaculture crab, which has great economical and nutritional value. To the best of our knowledge, few full-length crab transcriptomes are available. In this study, a library composed of 12 different tissues including gill, hepatopancreas, muscle, cerebral ganglion, eyestalk, thoracic ganglia, intestine, heart, testis, ovary, sperm reservoir, and hemocyte was constructed and sequenced using Pacific Biosciences single-molecule real-time (SMRT) long-read sequencing technology. A total of 284803 full-length non-chimeric reads were obtained, from which 79005 high-quality unique transcripts were obtained after error correction and sequence clustering and redundant. Additionally, a total of 52544 transcripts were annotated against protein database (NCBI nonredundant, Swiss-Prot, KOG, and KEGG database). A total of 23644 long non-coding RNAs (lncRNAs) and 131561 simple sequence repeats (SSRs) were identified. Meanwhile, the isoforms of many genes were also identified in this study. Our study provides a rich set of full-length cDNA sequences for S. paramamosain, which will greatly facilitate S. paramamosain research.

Characterization of cathepsin D from Eriocheir sinensis involved in Spiroplasma eriocheiris infection

Cathepsin D (catD) belongs to a lysosomal aspartic protease superfamily. The full-length catD cDNA from the Chinese mitten crab Eriocheir sinensis (EscatD) was 2748 bp and contained a 1158-bp ORF encoding a protein of 385 amino acids, including a signal peptide and two N-glycosylation sites. Phylogenetic analysis showed that EscatD was clustered into a single group, together with other catD for crustaceans. Quantitative real-time PCR revealed that EscatD was expressed mainly in the eyes, hemocytes, intestine and nerve and was expressed weakly in heart, muscle and gills. After challenge with Spiroplasma eriocheiris, the expression of EscatD was significantly up-regulated from 1 d to 9 d. The copy number of S. eriocheiris in a silencing EscatD group was significantly higher than those in the control groups during S. eriocheiris infection. Meanwhile, the survival rate of crabs decreased in an EscatD-dsRNA group. We further found that knockdown of EscatD by RNA interference resulted in a downward trend of expression levels of JNK, ERK, relish and p38 during the early stage, as well as a reduction in the expression of five antimicrobial peptides genes, namely, crusrin1, crustin2, ALF1, ALF2 and ALF3. The subcellular localization experiment suggested that recombinant EscatD was mainly located in the cytoplasm. The over-expression in Drosophila S2 cells indicated that EscatD could decrease the copy number of S. eriocheiris and increase cell viability. The above results demonstrated that EscatD plays an important immune role in E. sinensis to S. eriocheiris challenge.

Transcriptomic Analysis of Flower Bud Differentiation in Magnolia sinostellata

Magnolias are widely cultivated for their beautiful flowers, but despite their popularity, the molecular mechanisms regulating flower bud differentiation have not been elucidated. Here, we used paraffin sections and RNA-seq to study the process of flower bud differentiation in Magnolia sinostellata. Flower bud development occurred between 28 April and 30 May 2017 and was divided into five stages: undifferentiated, early flower bud differentiation, petal primordium differentiation, stamen primordium differentiation, and pistil primordium differentiation. A total of 52,441 expressed genes were identified, of which 11,592 were significantly differentially expressed in the five bud development stages. Of these, 82 genes were involved in the flowering. In addition, MADS-box and AP2 family genes play critical roles in the formation of flower organs and 20 differentially expressed genes associated with flower bud differentiation were identified in M. sinostellata. A qRT-PCR analysis verified that the MADS-box and AP2 family genes were expressed at high levels during flower bud differentiation. Consequently, this study provides a theoretical basis for the genetic regulation of flowering in M. sinostellata, which lays a foundation for further research into flowering genes and may facilitate the development of new cultivars.

Liver Transcriptome and miRNA Analysis of Silver Carp (Hypophthalmichthys molitrix) Intraperitoneally Injected With Microcystin-LR

Next-generation sequencing was used to analyze the effects of toxic microcystin-LR (MC-LR) on silver carp (Hypophthalmichthys molitrix). Silver carps were intraperitoneally injected with MC-LR, and RNA-seq and miRNA-seq in the liver were analyzed at 0.25, 0.5, and 1 h. The expression of glutathione S-transferase (GST), which acts as a marker gene for MC-LR, was tested to determine the earliest time point at which GST transcription was initiated in the liver tissues of the MC-LR-treated silver carps. Hepatic RNA-seq/miRNA-seq analysis and data integration analysis were conducted with reference to the identified time point. Quantitative PCR (qPCR) was performed to detect the expression of the following genes at the three time points: heme oxygenase 1 (HO-1), interleukin-10 receptor 1 (IL-10R1), apolipoprotein A-I (apoA-I), and heme binding protein 2 (HBP2). Results showed that the liver GST expression was remarkably decreased at 0.25 h (P < 0.05). RNA-seq at this time point revealed that the liver tissue contained 97,505 unigenes, including 184 significantly different unigenes and 75 unknown genes. Gene Ontology (GO) term enrichment analysis suggested that 35 of the 145 enriched GO terms were significantly enriched and mainly related to the immune system regulation network. KEGG pathway enrichment analysis showed that 18 of the 189 pathways were significantly enriched, and the most significant was a ribosome pathway containing 77 differentially expressed genes. miRNA-seq analysis indicated that the longest miRNA had 22 nucleotides (nt), followed by 21 and 23 nt. A total of 286 known miRNAs, 332 known miRNA precursor sequences, and 438 new miRNAs were predicted. A total of 1,048,575 mRNA–miRNA interaction sites were obtained, and 21,252 and 21,241 target genes were respectively predicted in known and new miRNAs. qPCR revealed that HO-1, IL-10R1, apoA-I, and HBP2 were significantly differentially expressed and might play important roles in the toxicity and liver detoxification of MC-LR in fish. These results were consistent with those of high-throughput sequencing, thereby verifying the accuracy of our sequencing data. RNA-seq and miRNA-seq analyses of silver carp liver injected with MC-LR provided valuable and new insights into the toxic effects of MC-LR and the antitoxic mechanisms of MC-LR in fish.

The RNA/miRNA data are available from the NCBI database Registration No. : SRP075165.