Essential roles of Cdc42 and MAPK in cadmium-induced apoptosis in Litopenaeus vannamei

Ajpacifastin-like is involved in the immune response of Apostichopus japonicus challenged by Vibrio splendidus

Pacifastin proteins are previously found to regulate the phenoloxidase system in invertebrates and arthropods. In this study, the immune response that was regulated by Ajpacifastin-like in the sea cucumber Apostichopus japonicus was determined. RNA interference was used to knock down the expression of the Ajpacifastin-like gene in A. japonicus, followed by challenge with Vibrio splendidus, and the colony count showed that the survival of V. splendidus in the si-Ajpacifastin group increased 4.64-fold compared to that of the control group. The purified recombinant Ajpacifastin-like showed an inhibitory effect on the extracellular protease activity of the supernatant collected from the V. splendidus culture. Consequently, a comparative transcriptome analysis of the coelomocytes from the control group and the si-Ajpacifastin group was performed to explore the global regulatory effect of the Ajpacifastin-like. A total of 1486 differentially expressed genes (DEGs) were identified, including 745 upregulated genes and 741 downregulated genes. GO enrichment showed that the DEGs were mainly enriched in translation, cytosolic ribosomal subunit and structural constituent of ribosome. KEGG analysis showed that the DEGs were significantly enriched in the retinoic acid-inducible gene I (RIG-I)-like receptor signaling pathway, antigen processing and presentation, toll-like receptor signaling pathway, mitogen-activated protein kinase signaling pathway, nuclear factor-kappa B signaling pathway and other immune-related pathways. Furthermore, real-time reverse transcriptase PCR was used to determine the RNA levels of six DEGs, i.e., cathepsinB, CYLD, caspase8, TRAF6, hsp90 and FADD, to verify the RNA-seq results. Overall, our results specified the immune response and pathways of A. japonicus in which Ajpacifastin-like was involved in.

In vitro immunotoxicity and possible mechanisms of 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) on Ruditapes philippinarum hemocytes

Marine bivalves can accumulate large amounts of pollutants from sea water, sediments and microalgae due to their filter-feeding habits. BDE-47 is often the most highly concentrated congener in bivalves. BDE-47 has been found to have toxic effects on bivalves, however, the immunotoxicity and the underlying mechanisms of BDE-47 on bivalves are not well understood yet. In this study, isolated hemocytes of Manila clam Ruditapes philippinarum were exposed to five concentrations of BDE-47 (6.25 μM, 12.5 μM, 25 μM, 50 μM, 100 μM), the effects of BDE-47 on hemocyte survival rate, cell viability, granulocyte ratio, phagocytosis, bacteriolytic activity, reactive oxygen species (ROS), lysosomal membrane permeability (LMP), superoxide dismutase (SOD), and phosphorylation state of extracellular regulated protein kinase (ERK) and p38 at 2 h, 6 h and 12 h were studied. The results indicated that BDE-47 exposure declined the hemocyte cell viability, reduced the granulocyte ratio, hampered the hemocyte phagocytosis and bacteriolytic activity, elevated the ROS levels, increased the LMP, significantly changed SOD expression and depressed the phosphorylation levels of ERK and p38. Taken together, the results demonstrated that BDE-47 had significant toxic effects on the immune function, and the immunotoxicity may partly via the overproduction of ROS and the alteration of MAPK signaling pathways.

Mechanism of Cadmium Exposure Induced Hepatotoxicity in the Mud Crab (Scylla paramamosain): Activation of Oxidative Stress and Nrf2 Signaling Pathway

Cadmium, one of the most toxic heavy metals, can cause severe oxidative damage to aquatic animals. However, the mechanism whereby the mud crabs respond to cadmium exposure remains unclear. This study investigated the effects of cadmium exposure on oxidative stress and histopathology changes and evaluated the role of the Nrf2 signaling pathway in regulating responses to cadmium-induced hepatotoxicity were investigated in mud crabs. Mud crabs were exposed to 0, 0.01, 0.05, and 0.125 mg/L cadmium for 21 d. The present results indicated that cadmium exposure increased hydrogen peroxide (H₂O₂) production, lipid peroxidation and tissue damage, but decreased the activity of superoxide dismutase (SOD) and catalase (CAT), and caused lipid peroxidation and tissue damage. The results of an integrated biomarker index analysis suggested that the toxicity of cadmium was positively related to cadmium concentration. The expression levels of the Nrf2 signaling pathway (Nrf2, metallothionein, and cytochrome P450 enzymes) were up-regulated after cadmium exposure. Silencing of Nrf2 in vivo decreased antioxidant gene (SOD, CAT, and glutathione S-transferase) expression, suggesting that Nrf2 can regulate antioxidant genes. Knocking down Nrf2 in vivo also significantly decreased the activity of SOD and CAT after cadmium exposure. Moreover, silencing of Nrf2 in vivo enhanced H₂O₂ production and the mortality rates of mud crabs after cadmium exposure. The present study indicated that cadmium exposure induced hepatotoxicity in the mud crab by increasing H₂O₂ content, which decreased the antioxidant capacity, leading to cell injury. In addition, the Nrf2 is activated to bound with antioxidant response element, initiating the expression of antioxidant enzyme genes during cadmium induced hepatotoxicity in the mud crabs.

The ARM repeat domain of hemocyanin interacts with MKK4 to modulate antimicrobial peptides expression

The mitogen-activated protein kinase (MAPK) intracellular signaling pathway mediates numerous biological processes, including antimicrobial immune response by inducing antimicrobial peptides (AMPs) production. Although MAPK signaling cascade proteins have been identified in penaeid shrimp, their modulation via the MKK4-p38-c-Jun cascade and effect on AMPs production is unknown. Here, we show that hemocyanin (PvHMC), antimicrobial peptides (anti-lipopolysaccharide factor, crustin, and penaeidins), and MKK4-p38-c-Jun cascade proteins are simultaneously induced by pathogens (Vibrio parahaemolyticus, Staphylococcus aureus, and white spot syndrome virus) in Penaeus vannamei. Intriguingly, knockdown of PvHMC with or without pathogen challenge attenuated the expression of MKK4-p38-c-Jun cascade proteins and their phosphorylation level, which consequently decreased AMPs expression. Further analysis revealed that PvHMC interacts via its armadillo (ARM) repeat domain with PvMKK4 to modulate the p38 MAPK signaling pathway. Thus, the ARM repeat domain enables penaeid shrimp hemocyanin to modulate AMPs expression during antimicrobial response by activating the p38 MAPK signaling pathway.

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Pathogens induce hemocyanin, MKK4-p38-c-Jun proteins, and antimicrobial peptide genes

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Hemocyanin modulates MKK4-p38-c-Jun cascade proteins to regulate AMPs gene expression

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Hemocyanin interacts with MKK4 to modulate p38 MAPK signaling in penaeid shrimp

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Deletion of the ARM repeat domain attenuates the interaction of hemocyanin with MKK4

FABP regulates fatty acid metabolism and oxidative response via PPARα/RXR signaling in Litopenaeus vannamei following environmental exposure of clofibric acid

Clofibric acid (CFA), a drug and personal care product, has been identified as ubiquitous in the aquatic system and surface water, causing pollution to the environment. In this study, after environmental (4 µg/L) levels of CFA challenge, the LvFABP, LvACS gene expressions, total haemocyte count (THC), relative enzymes (SOD1 and GST) activities in Litopenaeus vannamei were observed to decrease. In the meantime LvFATP, LvRXR expression and the level of NEFA were upregulated in L. vannamei body. LvFABP expression in vivo was knocked down by dsRNA-mediated RNA interference (RNAi), which led to significantly decreased levels of PPARα (including LvFATP, LvRXR and LvACS). When exposed to environmental CFA after 4 days, LvFABP knocked down group had a sharp upregulation of LvFATP, LvRXR, LvACS expression, GST activity and NEFA amount, following decreased THC and SOD1 activity. These results suggested that environmental concentration CFA may have some toxicological effect on L. vannamei, following fatty acids metabolism and oxidative stress responses by LvFABP via the PPARα/RXR signaling pathway, including LvFATP, LvRXR and LvACS.

Identification of co-chaperone Cdc37 in Penaeus monodon: coordination with Hsp90 can reduce cadmium stress-induced lipid peroxidation

Cell division cycle 37 (Cdc37) is an important cytoplasmic phosphoprotein, which usually functions as a complex with heat shock protein 90 (Hsp90), to effectively reduce the damage caused by heavy metals, such as cadmium (Cd), in aquatic animals. The high toxicity of Cd in aquatic systems generally has a deleterious effect on healthy farming of shrimps. In the present study, a novel Cdc37 gene from Penaeus monodon was identified and designated as PmCdc37. Following exposure to Cd stress, the expression levels of PmCdc37 were upregulated at the transcriptional level in both the hepatopancreas and hemolymph. RNA interference and recombinant protein injection experiments were carried out to determine the function of PmCdc37 in P. monodon following Cd exposure. To clarify the correlations between PmCdc37 and PmHsp90, the respective recombinant proteins were expressed in vitro, and the ATPase activity of PmHsp90, with or without PmCdc37, was assessed. Moreover, a pull-down assay was conducted to detect the correlation between PmCdc37 and PmHsp90. After analyzing the expression patterns of PmHsp90 following Cd challenge, whether PmHsp90 can promote the ability of PmCdc37 to resist Cd stress or not was investigated. The results showed that formation of a PmHsp90/PmCdc37 complex protected shrimp against Cd stress-induced damage. Moreover, we also confirmed that PmSOD is involved in Cd stress, and that the PmHsp90/PmCdc37 complex can regulate SOD enzymatic activity. PmSOD was involved in decreasing the MDA content in shrimp hemolymph caused by Cd stress. We concluded that during exposure to Cd, the PmHsp90/PmCdc37 complex increases SOD enzyme activity, and in turn decreases the MDA content, thereby protecting shrimp against the damage caused by Cd stress. The present studies contribute to understanding the molecular mechanism underlying resistance to Cd stress in shrimp.

The mechanism of Mitogen-Activated Protein Kinases to mediate apoptosis and immunotoxicity induced by Benzo[a]pyrene on hemocytes of scallop Chlamys farreri in vitro

Benzo [a]pyrene (B [a]P) has received widespread attention for serious pollution in the sea, which may reduce immunity and lead to the outbreak of disease in bivalves. However, the mechanism of immunotoxicity induced by B [a]P in bivalves was still unclear. Previous studies have found that Mitogen-Activated Protein Kinases (MAPKs) including three classic pathways (ERK, p38 and JNK) play an important role in mediating this process. Thus, in order to explore the mechanism of immunotoxicity induced by B [a]P in scallop Chlamys farreri, hemocytes were treated with PD98059 (ERK inhibitor), SB203580 (p38 inhibitor) and SP600125 (JNK inhibitor) for 1 h and then incubation with B [a]P for 24 h at 1 μg/mL. Indexes including oxidative damage, apoptotic rate, and immune indicators were detected in the present study. The results showed that the increase of Reactive Oxygen Species (ROS) and DNA damage induced by B [a]P was inhibited with PD98059 and SB203580. Besides, lysosomal membrane stability (LMS) damage was promoted by PD98059, while it was opposite when treated with SB203580. Moreover, the ascended apoptosis rate induced by B [a]P was increased significantly after treatment with PD98059, but it was remarkably attenuated by SB203580 and SP600125. However, the opposite pattern was showed in phagocytosis compared with apoptosis rate in all of three inhibitors. In addition, antibacterial activity and bacteriolytic activity were enhanced by SB203580 while inhibited by PD98059. Therefore, these results showed that MAPKs directly or indirectly mediate the decrease of oxidative damage, apoptosis and immune defense ability of C. farreri hemocytes, which suggesting ERK/p38/JNK pathways have different functions in the apoptosis and immunity of C. farreri hemocytes after B [a]P exposure. In conclusion, this study intended to enrich the theoretical basis for immunotoxicology of bivalves exposed to pollutants.

Molecular characterization of p38 MAPK and tissue-specific expression under cadmium stress in red swamp crayfish (Procambarus clarkii)

Keeping harmful pollutants out of some crucial tissues as much as possible is a key trait for the organism to survive in adverse conditions, such as in heavy-metal contaminated aquatic environments. In the current study, it was hypothesized that the p38 Mitogen-activated Protein Kinase (MAPK) controls the distribution of cadmium (Cd) in red swamp crayfish (Procambarus clarkii) by regulating the accumulation of Cd in different tissues under Cd-stressed conditions. To test this hypothesis, this study analyzed the p38 MAPK gene and compared the differential expression levels in the heart, antennal gland, gill, hepatopancreas, and muscles. Differences in expression levels of p38 MAPK gene between different tissues were conducted under controlled Cd exposure. This study found that the expression of p38 MAPK is tissue-specific in all tested samples under non-stressed condition. Under Cd-stressed condition and with the prolongation of Cd exposure time, the content of Cd in all examined tissues of P. clarkii has substantially increased compared to the control, although the Cd contents in the heart, antennal gland, and muscle remained relatively lower than those observed in the hepatopancreas. Consequently, the levels of p38 MAPK in the heart, antennal gland, and muscle were higher than the level in the hepatopancreas. These results indicate that p38 MAPK regulates the distribution and accumulation of Cd in different tissues of P. clarkii under Cd-stressed condition. Furthermore, the results suggested that the higher expression of p38 MAPK played a crucial role in keeping Cd out of the tissues in the Cd-rich aquatic environment to maintain the normal physiological function of the red swamp crayfish, a process necessary for survival and growth.

Increasing ERK phosphorylation by inhibition of p38 activity protects against cadmium-induced apoptotic cell death through ERK/Drp1/p38 signaling axis in spermatocyte-derived GC-2spd cells

Many studies report that cadmium chloride (CdCl₂)-induces oxidative stress is associated with male reproductive damage in the testes. CdCl₂ also induces mitochondrial fission by increasing dynamin-related protein 1 (Drp1) expression as well as the mitochondria-dependent apoptosis pathway by extracellular signal-regulated kinase (ERK) activation. However, it remains unclear whether mechanisms linked to the mitochondrial damage signal via CdCl₂-induced mitogen-activated protein kinases (MAPK) cause damage to spermatocytes. In this study, increased intracellular and mitochondrial reactive oxygen species (ROS) levels, mitochondrial membrane potential (∆Ψm) depolarization, and mitochondrial fragmentation and swelling were observed at 5 μM of CdCl₂ exposure, resulting in increased apoptotic cell death. Moreover, CdCl₂-induced cell death is closely associated with the ERK/Drp1/p38 signaling axis. Interestingly, SB203580, a p38 inhibitor, effectively prevented CdCl₂-induced apoptotic cell death by reducing ∆Ψm depolarization and intracellular and mitochondrial ROS levels. Knockdown of Drp1 expression diminished CdCl₂-induced mitochondrial deformation and ROS generation and protected GC-2spd cells from apoptotic cell death. In addition, electron microscopy showed that p38 inhibition reduced CdCl2-induced mitochondrial interior damage more effectively than N-acetyl-L-cysteine (NAC), an ROS scavenger; ERK inhibition; or Drp1 knockdown. Therefore, these results demonstrate that inhibition of p38 activity prevents CdCl₂-induced apoptotic GC-2spd cell death by reducing depolarization of mitochondrial membrane potential and mitochondrial ROS levels via ERK phosphorylation in a signal pathway different from the CdCl₂-induced ERK/Drp1/p38 axis and suggest a therapeutic strategy for CdCl₂-induced male infertility.

Biochemical and molecular responses of cyprinids in two Mediterranean lacustrine ecosystems: Opportunities for ecological assessment and biomonitoring

Lacustrine ecosystems have been altered by accelerating pollution, excessive nutrient and organic load, water abstraction, and are susceptible to climate change. Hence, suggesting sensitive and reliable biomarkers for early assessments of their status is of urgent need. In this study, two freshwater commercial fish species, Cyprinus carpio (carp) and Carassius gibelio (prussian carp) from two lakes (i.e. Koronia and Volvi, Northern Greece) with different anthropogenic pressures were used and a battery of biochemical and molecular biomarkers related to stress response were analyzed in fish gills and liver. In parallel, water physicochemical parameters (T, DO, pH, conductivity, salinity), BOD₅ and nutrient (N-NO₃, N-NO₂, N-NH₄, P-PO₄) concentrations were measured. Results showed that Lake Koronia had higher conductivity and salinity values and N-NO₂ concentrations. Levels of Heat Shock Response (HSR), MAPK phosphorylation, protein carbonylation, lipid peroxidation products, Bax/Bcl-2 ratio, ubiquitination and caspases were increased in gills and liver of both fish species sampled from Lake Koronia in relation to those of Lake Volvi. Likewise, liver lipid content was increased in both fish species sampled from Lake Koronia compared to those sampled from Lake Volvi. The results indicate and reflect the higher environmental degradation that prevails in Lake Koronia ecosystem in comparison to that of Lake Volvi. The fish species studied showed different susceptibility depending on the biomarkers examined. In addition, our results from both examined species provide insight into the mechanisms involved in acclimatization to stressful environments and support the role of the studied biomarkers as sensitive and reliable tools for ecological assessments of lake ecosystems in biomonitoring studies.

The role of delta-1-pyrroline-5-carboxylate dehydrogenase (P5CDh) in the Pacific white shrimp (Litopenaeus vannamei) during biotic and abiotic stress

Proline (Pro) metabolism is intimately associated with stress adaptation. The catabolism of Pro includes two dehydrogenation reactions catalyzed by proline dehydrogenase (ProDH) and Δ¹-pyrroline-5-carboxylate dehydrogenase (P5CDh). P5CDh is a mitochondrial matrix NAD⁺-dependent dehydrogenase that is critical in preventing P5C-Pro intensive cycling and avoiding ROS production from electron run-off. Little is known about the roles of P5CDh in invertebrates, however. We cloned the P5CDh sequence in the Pacific white shrimp, Litopenaeus vannamei, and found that LvP5CDh is expressed predominantly in pleopod, hepatopancreas and gill. Subcellular localization analysis revealed that LvP5CDh protein was mainly found in the cytoplasm. In addition, overexpressing LvP5CDh in cells reduced ROS formation and inhibited apoptosis induced by LC₅₀ Cd²⁺. Shrimp were exposed to various stress factors including infection with Vibrio alginolyticus, (½ LC₅₀ and LC₅₀) Cd²⁺, acid (pH 5.6) and alkali stress (pH 9.3). Both biotic and abiotic stress resulted in increased LvP5CDh expression and Pro accumulation; V. alginolyticus infection, pH 9.3 and LC₅₀ Cd²⁺ stress apparently stimulated the Glu pathway of Pro synthesis, while pH 5.6 and ½ LC₅₀ Cd²⁺ stress promoted the Orn pathway of Pro synthesis. Silencing of Lvp53 in shrimp attenuated LvP5CDh expression during Cd²⁺ stress, but had no effect on LvP5CDh mRNA levels if no Cd²⁺ stress was imposed. Our study contributes to the functional characterization of LvP5CDh in biotic and abiotic stress and reveals it to protect against ROS generation, damage to the cell, including the mitochondria, and apoptosis. Thus, LvP5CDh plays a critical role in immune defense and antioxidant responses.

cDNA cloning and expression analysis of glutaredoxin (Grx) 2 in the Pacific white shrimp Litopenaeus vannamei

Glutaredoxin (Grx) is a class molecule oxidoreductase, which can regulate the redox state of proteins and plays a key role in antioxidant defense. However, the informations of Grx cDNA sequences and their functions are lack in decapod crustacea. In the present study, the cDNA of LvGrx 2 was cloned from the Pacific white shrimp, Litopenaeus vannamei. The open reading frame (ORF) of LvGrx 2 was 360 bp, which encoded a polypeptide of 119 amino acids. The molecular mass of the predicted protein is 12.87 kDa with an estimated pI of 8.22. Sequence alignment showed that the amino acid sequence of LvGrx 2 shares 59%, 59% and 58% identity with that of the coelacanth Latimeria chalumnae, the plateau frog Nanorana parkeri and the half-smooth tongue sole Cynoglossus semilaevis, respectively. Quantitative real-time PCR analysis revealed that LvGrx 2 were detected in a wide range of tissues, with highest expression in gill, hepatopancrea and intestine, and weakest expression in muscle. The expression responses of LvGrx 2 were analyzed in hepatopancrea and gill after ammonia-N stress or lipopolysaccharide (LPS) injection. During ammonia-N exposure, the LvGrx 2 transcriptions in hepatopancrea and gill significantly up-regulated, and the peak value appeared after 12 h and 24 h exposure respectively. After LPS injection, expression levels of LvGrx 2 in hepatopancrea obviously increased in the early and late stages, while LvGrx 2 transcription in gill sharply up-regulated in the middle period. These results suggest that LvGrx 2 may play a vital role in shrimp defense system against environmental stress and pathogen infection. RNA interference experiment was designed to further probe roles of LvGrx 2 during ammonia-N exposure. Ammonia-N induced obvious improvement in expression levels of LvGrx 2, LvGrx 3, GPx, GST and Trx, accompanied by increases of protein carbonyl and malondialdehyde (MDA) contents. However, transcription of GPx and GST were much weaker in LvGrx 2 interfered-shrimp, and oxidative damage in both lipid and protein were more serious. These results further suggest that LvGrx 2 in shrimp participates in oxidative defence and regulation of antioxidant system.

Molecular characterization and function analysis of a nucleotide excision repair gene Rad23 from Litopenaeus vannamei after Vibrio alginolyticus challenge

Nucleotide excision repair (NER) removes many different types of DNA lesions, and NER related host factors are reported to aid recovery steps during viral integration. Here, we report the identification and characterization of a DNA repair gene Rad23 from Litopenaeus vannamei and explore its role in innate immunity of crustaceans. LvRad23 contains a1149 bp open reading frame (ORF) which encodes a 382 amino acids protein with predicted theoretical isoelectric point of 4.21. LvRad23 was ubiquitously expressed in the muscle, eyestalk, gill, stomach, heart, legs, intestine, and hepatopancreas in order from high to low and LvRad23 protein was showed to be located in the cytoplasm of Drosophila S2 cells. The homology analysis showed that it has a high sequence homology with Rad23 protein from Marsupenaeus japonicus. Vibrio alginolyticus challenge induced a remarkable up-regulation of LvRad23 mRNA in hepatopancreas. Knocking down LvRad23can interfere the NER pathway by down regulating the expression of replication protein A (RPA) and proliferating cell nuclear antigen (PCNA). However it didn't cause any significant difference on total hemocyte count (THC) between LvRad23-silenced and non-silenced group.LvRad23-silenced then challenge with V. alginolyticus inducing high level of reactive oxygen species (ROS) and DNA damage in hemolymph. As well as decreased THC, which seriously diminished the innate immune system of L. vannamei. Meanwhile, the NER pathway was reactived by enhancing the expression of LvRad23 and promoting the production of LvPCNA to resist apoptosis and maintain proliferation of hemolymph cells in the later stage. Our results suggest that LvRad23 plays a vital role in shrimp specific immune response to V. alginolytcus through its participation in NER pathway.

Comparative transcriptomics analysis of the river pufferfish (Takifugu obscurus) by tributyltin exposure: Clues for revealing its toxic injury mechanism

TBT residual in water had become a noticeable ecological problem for aquatic ecosystems. The river pufferfish (Takifugu obscurus) is a kind of an anadromous fish species and widely distributed in the East China Sea and the Yellow Sea. Because of the water contamination, the pufferfish wild resource had a sudden decline in recent years. Therefore, the study on the response of pufferfish to the TBT exposure may contribute to reveal toxic injury mechanism of T. obscurus under TBT exposure. In this study, the transcriptional library of T. obscurus liver and gill was constructed and sequenced by an improved Illumina HiseqX10 high-throughput sequencing platform under different concentrations of TBT acute stress. The blood cell numbers distinctly decreased after TBT exposure, showing the adverse effects of TBT invasion and self-adjusting ability of the pufferfish. The production of reactive oxygen species increased, demonstrating the oxidation resistance of T. obscurus when exposed to TBT. The obtained data were compared with the genome data of Takifugu rubripes and transcriptional resource database. On this basis, gene function annotation, analysis and classification were carried out by bioinformatics method, and differential genes related to toxic injury function were screened out. Meanwhile, new toxic related genes and related signal pathways were sought to provide new theoretical guidance for the pathogenesis of T. obscurus exposed to TBT. This study not only enriched the transcriptome data of T. obscurus under environmental stress, but also provided a new research method for the response mechanism of T. obscurus under the stimulation of environmental factors.

LvCdc42 is a potential negative regulator of Lvp53 in Litopenaeus vannamei exposed to Vibrio alginolyticus stress

As a crucial molecular switch, Cdc42 is a signal regulation hub which is involved in a wide range of cellular processes, including cytokinesis, gene expression, cell cycle progression and apoptosis. It has been reported that this GTPase promotes host defense against fatal infection and plays a vital role in the innate immunity system of mammals. But whether and how Cdc42 participates in innate immunity in invertebrates, such as the shrimp Litopenaeus vannamei, is still unknown. In this study, confocal microscopy analysis showed that LvCdc42 located in both cytoplasm and nucleus of S2 cells depended on its structure. The silencing LvCdc42 induced an increase in the expression of Lvp53 and Lvcaspase-3. When LvCdc42-silenced shrimps were stressed with Vibrio alginolyticus, the expression of Lvp53 and Lvcaspase-3 was markedly up-regulated. Moreover, the increase in the apoptosis rate in hemocytes and in cumulative mortality were in line with Lvp53 mRNA expression. These data suggest that the molecular switch LvCdc42 acts as a negative regulator of Lvp53 and participates in the apoptosis of hemocytes when L. vannamei is challenged with V. alginolyticus.

Cross-reactivities of mammalian MAPKs antibodies in rotifer and copepod: Application in mechanistic studies in aquatic ecotoxicology

The mitogen-activated protein kinases (MAPKs) family is known to mediate various biological processes in response to diverse environmental pollutants. Although MAPKs are well characterized and studied in vertebrates, in invertebrates the cross-reactivities of MAPKs antibodies were not clearly known in response to environmental pollutants due to limited information of antibody epitopes with material resources for invertebrates. In this paper, we performed phylogenetic analysis of MAPKs genes in the marine rotifer Brachionus koreanus and the copepods Paracyclopina nana and Tigriopus japonicus. Also in rotifer and copepods, several studies of Western blot of MAPK signaling pathways were shown in response to environmental pollutants, including multi-walled carbon nanotubes (MWCNTs), water-accommodated fractions (WAFs) of crude oil, and microplastics. This paper will provide a better understanding of the underlying mechanistic scenario in terms of cross-reactivities of mammalian antibodies in rotifer and copepod.

Molecular cloning, characterization and function of a germinal center kinase MST4 gene from Litopenaeus vannamei in response to Vibrio alginolyticus challenge in TLR-TRAF6 signaling pathway

The serine/threonine protein kinase MST4 plays multiple roles in the regulation of signaling pathways that govern cellular processes including mitosis, migration, homeostasis, polarity, proliferation, differentiation and apoptosis. Here we report the identification and characterization of the full-length sequence of LvMST4 from the shrimp L. vannamei, and investigations into its role in the shrimp's immune response to infection by the pathogenic bacterium Vibrio alginolyticus. Subcellular localization assays demonstrated the enzyme's presence in the shrimp's cytoplasm, and tissue-specific expression analysis revealed that it is expressed ubiquitously but at different levels in different tissues. Infection with V. alginolyticus increased LvMST4 expression and induced a rapid response via the TLR-TRAF6 signaling pathway, causing a decline in the total hemocyte count (THC) and an increase in respiratory burst (RB) activity. In non-infected shrimp, RNAi silencing of LvMST4 with dsRNA had no significant effect on THC but seemed to activate the TRAF6-MKK6-p38 pathway and reduced RB activity. In shrimp challenged with V. alginolyticus, LvMST4 silencing reduced bacterial clearance and increased the initial upregulation of LvTRAF6 while reducing the expression of LvMKK6 and Lvp38. LvMST4 silencing also slightly reduced the THC but caused pronounced increases in RB activity and cumulative mortality. These findings suggest that LvMST4 contributes to antimicrobial responses via the TLR-TRAF6 signal pathway, and helps maintain immunological homeostasis in L. vannamei.

Functional and molecular responses of the blue mussel Mytilus edulis' hemocytes exposed to cadmium - An in vitro model and transcriptomic approach

The bivalve mollusk, Mytilus edulis, is used as a sentinel species in several monitoring programs due to its ability to bio-accumulate contaminants. Its immune system consists of hemocytes and humoral components, which constitute the main part of the hemolymph. The present study is aimed at understanding the effects of Cd on the differentially expressed genes involved in the phagocytosis of M. edulis' hemocytes. Our approach focuses on an in vitro model by exposing hemocytes to different concentrations of Cd ranging from 10^-9 M to 10^-3 M. Phagocytosis and cell viability as functional markers were measured using flow cytometry. The molecular mechanisms regulated by Cd were investigated using RNA-seq and DGE analysis. Results showed that viability and phagocytosis of hemocytes exposed to 10^-3 M of Cd were significantly decreased after 21 h of exposure. RNA sequencing data showed that 1112 transcripts (out of 352,976 contigs) were differentially regulated by the highest concentration of Cd. Among these identified transcripts, 1028 and 84 were up and down-regulated respectively. The induction of super oxide dismutase (SOD), glutathion-s-transferase (GST), cytochrome P450 2C8 (CYP2C8), multidrug resistance protein (MRP1) and heat shock protein 70 (HSP70) suggests that Cd can regulate key molecular mechanisms. In addition, several toll-like receptors (TLR) as well as genes involved in phagocytosis (actin and CDC42) and apoptosis (caspase 8 and XIAP/IAP) were induced by Cd. Thus, our model highlights the effect of Cd on the phagocytic function of M. edulis' hemocytes along with the regulation of gene expression involved in innate immunity, detoxification and apoptosis. Further investigations need to be pursued to unravel the effects of Cd on the molecular mechanisms identified in this study.

Molecular Characterization and Expression Analysis of P38 MAPK Gene and Protein in Aquatic Midge, Chironomus riparius (Diptera: Chironomidae), Exposed to Environmental Contaminants

P38 Mitogen-activated protein kinase (MAPK), an important signaling protein involved in various cellular processes, including stress responses, has been well characterized in model organisms. P38 has been identified in a number of insects, including the genus Drosophila; however, its homologue in Chironomus riparius has not yet been identified. In this study, we identified and characterized p38 MAPK (Crp38) gene in C. riparius using a transcriptome database that was previously generated 454 GS-FLX pyrosequencing. Comparative and phylogenetic analyses were performed using the p38 homologue of other species, such as Drosophila melanogaster, Aedes aegypti, Bombyx mori, Caenorhabditis elegans, Homo sapiens, etc. Furthermore, to test its potential as a biomarker of environmental contamination, Crp38 gene expression was analyzed upon exposure to nonylphenol (NP), silver nanoparticles (AgNPs), and cadmium (Cd). Crp38 gene expression was up- or down-regulated depending on the concentration and exposure duration of chemicals. These results show the role of Crp38 gene in defense against environmental stresses, as well as its potential use as a biomarker for various environmental pollutants. We further synthesized p38 antibody based on the predicted amino acid sequence deduced from Crp38 cDNA and, using this customized antibody, examined p38 protein expression in Cd exposed C. riparius. Although transcriptional alteration was not translated to the protein level, this result showed the possible application of a protein level functional study using cDNA sequence information from next-generation sequencing database in nonmodel organisms.

Hypoxia drives apoptosis independently of p53 and metallothionein transcript levels in hemocytes of the whiteleg shrimp Litopenaeus vannamei

The cellular mechanisms used by the shrimp Litopenaeus vannamei to respond to hypoxia have been studied from the energetic metabolism and antioxidant angles. We herein investigated the participation of p53 and metallothionein (MT) in the apoptotic process in response to hypoxia in shrimp hemocytes. The Lvp53 or LvMT genes were efficiently silenced by injection of double stranded RNA for p53 or MT. The effects of silencing on apoptosis were measured as caspase-3 activity and flow cytometry in hemocytes after 24 and 48 h of hypoxia (1.5 mg DO L(-1)). Hemocytes from unsilenced animals had significantly higher apoptosis levels upon both times of hypoxia. The apoptotic levels were diminished but not suppressed in dsp53-silenced but not dsMT-silenced hemocytes after 24 h of hypoxia, indicating a contribution of Lvp53 to apoptosis. Apoptosis in normoxia was significantly higher in dsp53-and dsMT-silenced animals compared to the unsilenced controls, pointing to a possible cytoprotective role of LvMT and Lvp53 during the basal apoptotic program in normoxia. Overall, these results indicate that hypoxia augments apoptosis in shrimp hemocytes and high mRNA levels of Lvp53 and LvMT are not necessary for this response.

Molecular characterization and function of a PTEN gene from Litopenaeus vannamei after Vibrio alginolyticus challenge

PTEN, a tumor suppressor gene, suppresses cell survival, growth, apoptosis, cell migration and DNA damage repair by inhibiting the PI3K/AKT signaling pathway. In this study, the full-length Litopenaeus vannamei PTEN (LvPTEN) cDNA was obtained, containing a 5'UTR of 59bp, an ORF of 1269bp and a 3'UTR of 146bp besides the poly (A) tail. The PTEN gene encoded a protein of 422 amino acids with an estimated molecular mass of 48.3 KDa and a predicted isoelectric point (pI) of 7.6. Subcellular localization analysis revealed that LvPTEN was distributed in both cytoplasm and nucleus, and the tissue distribution patterns showed that LvPTEN was ubiquitously expressed in all the examined tissues. Vibrio alginolyticus challenge induced upregulation of LvPTEN expression. Moreover, RNAi knock-down of LvPTEN in vivo significantly increased the expression of LvAKT mRNA, while reducing that of the downstream apoptosis genes LvP53 and LvCaspase3. LvPTEN knock-down also caused a sharp increase in cumulative mortality, bacterial numbers, and DNA damage in the hemolymph of L. vannamei following V. alginolyticus challenge, together with a sharp decrease in the total hemocyte count (THC). These results suggested that LvPTEN may participate in apoptosis via the PI3K/AKT signaling pathway in L. vannamei, and play an important role in shrimp innate immunity.

Genetic and Histopathological Responses to Cadmium Toxicity in Rabbit's Kidney and Liver: Protection by Ginger (Zingiber officinale)

This study aimed to examine the protective effects of ginger (G) on the genetic response induced by cadmium (Cd) and immunohistochemical expression of Caspase3 and MKI67 in the kidney and liver of rabbits. Male rabbits were divided into three groups; each group contains 10 animals: group (C) received basic diet and tap water for 12 weeks, the second group (Cd) received 200 mg/kg b.w CdCl2 in water for 12 weeks, group (Cd + G) was given 200 mg/kg b.w CdCl2 in water and 400 mg ginger/kg b.w in food for 12 weeks. Cd administration increased the activity of mRNA expression of the examined apoptotic (Caspase3), proliferation (MKI67), proto-oncogene (C-fos), and antioxidant (GST), while decreased the expression of anti-apoptotic (Bcl2). Ginger counteracted the effects of Cd in (Cd + G) group and downregulated the previously upregulated genes under Cd administration appeared in (Cd) group. The immunohistochemical expression of Caspase3 and MKI67 in the liver and kidney cells of the (C) group was shown very faint to negative reactions, strong staining in hepatocytes and the tubular epithelium in cadmium-treated group, while slight staining in some hepatocytes and tubular epithelium in co-administration with ginger in (Cd + G) group. In conclusion, ginger administration showed a protective effect against cadmium toxicity.

The GRIM-19 plays a vital role in shrimps' responses to Vibrio alginolyticus

GRIM-19 (gene associated with retinoid-interferon-induced mortality 19), a novel cell death regulatory gene, plays important roles in cell apoptosis, mitochondrial respiratory chain and immune response. It has been reported to interact physically with STAT3 and inhibit STAT3-dependent signal transduction. In this study, a new GRIM-19 gene, which is a 789-bp gene encoding a 149 amino acids protein, is identified and characterized from Litopenaeus vannamei. The tissue distribution patterns showed that LvGRIM-19 was widely expressed in all examined tissues, with the highest expression in muscle. Quantitative real-time PCR revealed that LvGRIM-19 was down-regulated in hepatopancreas after infection with the Vibrio alginolyticus. Knockdown of LvGRIM-19 by RNA interference resulted in a lower mortality of L. vannamei under V. alginolyticus infection, as well as an enhancement in the protein expression of STAT gene and JAK gene. V. alginolyticus infection caused an increase apoptotic cell ratio and ROS production of L. vannamei, while LvGRIM-19 silenced shrimps showed significantly lower than GFP group. Our results suggest that the GRIM-19 plays a vital role in shrimps' responses to V. alginolyticus. Interferenced LvGRIM-19 treatment during V. alginolyticus infection could increase 12 h survival rate, which might indicated that LvGRIM-19 is closely related to death of shrimps.

The Rho GTPase Family Genes in Bivalvia Genomes: Sequence, Evolution and Expression Analysis

Background

Rho GTPases are important members of the Ras superfamily, which represents the largest signaling protein family in eukaryotes, and function as key molecular switches in converting and amplifying external signals into cellular responses. Although numerous analyses of Rho family genes have been reported, including their functions and evolution, a systematic analysis of this family has not been performed in Mollusca or in Bivalvia, one of the most important classes of Mollusca.

Results

In this study, we systematically identified and characterized a total set (Rho, Rac, Mig, Cdc42, Tc10, Rnd, RhoU, RhoBTB and Miro) of thirty Rho GTPase genes in three bivalve species, including nine in the Yesso scallop Patinopecten yessoensis, nine in the Zhikong scallop Chlamys farreri, and twelve in the Pacific oyster Crassostrea gigas. Phylogenetic analysis and interspecies comparison indicated that bivalves might possess the most complete types of Rho genes in invertebrates. A multiple RNA-seq dataset was used to investigate the expression profiles of bivalve Rho genes, revealing that the examined scallops share more similar Rho expression patterns than the oyster, whereas more Rho mRNAs are expressed in C. farreri and C. gigas than in P. yessoensis. Additionally, Rho, Rac and Cdc42 were found to be duplicated in the oyster but not in the scallops. Among the expanded Rho genes of C. gigas, duplication pairs with high synonymous substitution rates (Ks) displayed greater differences in expression.

Conclusion

A comprehensive analysis of bivalve Rho GTPase family genes was performed in scallop and oyster species, and Rho genes in bivalves exhibit greater conservation than those in any other invertebrate. This is the first study focusing on a genome-wide characterization of Rho GTPase genes in bivalves, and the findings will provide a valuable resource for a better understanding of Rho evolution and Rho GTPase function in Bivalvia.

Allograft inflammatory factor-1 in grass carp (Ctenopharynogodon idella): Expression and response to cadmium exposure

Allograft Inflammatory Factor-1 (AIF-1) is an inflammation responsive protein that is mainly produced by immunocytes. As a pro-inflammatory cytokine, AIF-1 is a key moderator in host immune defense reaction. However, the inflammatory properties of AIF-1 in freshwater fish still hasn't been clearly elucidated. In the present study, AIF-1 was identified from grass carp (Ctenopharynogodon idella). It's transcript was found in all examined tissues including brain, spleen, kidney, liver, heart, while a relative low level in red muscle, gill, thymus, white muscle, intestine and fin. Furthermore, AIF-1 transcription and expression level decreased in spleen and didn't change a lot in kidney with cadmium induction, respectively. The result indicated that grass carp AIF-1 might be involved in cadmium-induced stress.