The cyclin-dependent kinase 2 (CDK2) mediates hematopoiesis through G1-to-S transition in Chinese mitten crab Eriocheir sinensis

PyLKB1 regulates glucose transport via activating PyAMPKα in Yesso Scallop Patinopecten yessoensis under high temperature stress

Liver kinase B1 (LKB1) is a classical serine/threonine protein kinase and plays an important role in maintaining energy homeostasis through phosphorylate AMP-activated protein kinase α subunit (AMPKα). In this study, a homologous molecule of LKB1 with a typical serine/threonine kinase domain and two nuclear localization sequences (NLSs) was identified in Yesso Scallop Patinopecten yessoensis (PyLKB1). The mRNA transcripts of PyLKB1 were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in hepatopancreas. PyLKB1 was mainly located in cytoplasm and nucleus of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyLKB1, PyAMPKα, and PyGLUT1 in hepatopancreas, the phosphorylation level of PyAMPKα at Thr170 in hepatopancreas, the positive fluorescence signals of PyLKB1 in haemocytes, glucose analogue 2-NBDG content in haemocytes, and glucose content in hepatopancreas, haemocytes and serum all increased significantly (p < 0.05) compared to blank group (15 °C). However, there was no significant difference at the protein level of PyLKB1 and PyAMPKα. After PyLKB1 was knockdown by siRNA, the mRNA expression level of PyGLUT1, and the glucose content in hepatopancreas and serum were significantly down-regulated (p < 0.05) compared with the negative control group receiving an injection of siRNA-NC. However, there were no significant difference in PyGLUT1 expression, glucose content and glucose analogue 2-NBDG content in haemocytes. These results collectively suggested that PyLKB1-PyAMPKα pathway was activated to promote glucose transport by regulating PyGLUT1 in response to high temperature stress. These results would be helpful for understanding the function of PyLKB1-PyAMPKα pathway in regulating glucose metabolism and maintaining energy homeostasis under high temperature stress in scallops.

Potential molecular mechanism underlying the harmed haemopoiesis upon Benzo[a]pyrene exposure in Chlamys farreri

Benzo[a]pyrene (B[a]P), a ubiquitous contamination in the marine environments, has the potential to impact the immune response of bivalves by affecting the hemocyte parameters, especially total hemocyte count (THC). THC is mainly determined by haematopoietic mechanisms and apoptosis of hemocytes. Many studies have found that B[a]P can influence the proliferation and differentiation of hemocytes. However, the link between the toxic mechanisms of haematopoietic and environmental pollutants is not explicitly stated. This study is to investigate the toxic effects of B[a]P on haematopoietic mechanisms in C. farreri. Through the tissue expression distribution experiment and EDU assay, gill is identified as a potential haematopoietic tissue in C. farreri. Subsequently, the scallops were exposed to B[a]P (0.05, 0.5, 5 μg/L) for 1d, 3d, 6d, 10d and 15d. Then BPDE content, DNA damage, gene expression of haematopoietic factors and haematopoietic related pathways were determined in gill and hemocytes. The results showed that the expression of CDK2 was significantly decreased under B[a]P exposure through three pathways: RYR/IP3-calcium, BPDE-CHK1 and Notch pathway, resulting in cell cycle arrest. In addition, B[a]P also significantly reduced the number of proliferating hemocytes by affecting the Wnt pathway. Meanwhile, B[a]P can significantly increase the content of ROS, causing a downregulation of FOXO gene expression. The gene expression of Notch pathway and ERK pathway was also detected. The present study suggested that B[a]P disturbed differentiation by multiple pathways. Furthermore, the expression of SOX11 and CD9 were significantly decreased, which directly indicated that differentiation of hemocytes was disturbed. In addition, phagocytosis, phenoloxidase activity and THC were also significant decreased. In summary, the impairment of haematopoietic activity in C. farreri further causes immunotoxicity under B[a]P exposure. This study will improve our understanding of the immunotoxicity mechanism of bivalve under B[a]P exposure.

The involvement of AMP-activated protein kinase α in regulating glycolysis in Yesso scallop Patinopecten yessoensis under high temperature stress

AMP-activated protein kinase α subunit (AMPKα), the central regulatory molecule of energy metabolism, plays an important role in maintaining energy homeostasis and helping cells to resist the influence of various adverse factors. In the present study, an AMPKα was identified from Yesso scallop Patinopecten yessoensis (PyAMPKα). The open reading frame (ORF) of PyAMPKα was of 1599 bp encoding a putative polypeptide of 533 amino acid residues with a typical KD domain, a α-AID domain and a α-CTD domain. The deduced amino acid sequence of PyAMPKα shared 59.89-74.78% identities with AMPKαs from other species. The mRNA transcripts of PyAMPKα were found to be expressed in haemocytes and all the examined tissues, including gill, mantle, gonad, adductor muscle and hepatopancreas, with the highest expression level in adductor muscle. PyAMPKα was mainly located in cytoplasm of scallop haemocytes. At 3 h after high temperature stress treatment (25 °C), the mRNA transcripts of PyAMPKα, the phosphorylation level of PyAMPKα at Thr170 and the lactic acid (LD) content in adductor muscle all increased significantly, while the glycogen content decreased significantly. The activity of pyruvate kinase (PyPK) and the relative mRNA expression level of phosphofructokinase (PyPFK) were significantly up-regulated at 3 h after high temperature stress treatment (25 °C). Furthermore, the PyAMPKα activator AICAR could effectively upregulate the phosphorylation level of PyAMPKα, and increase activities of PyPFK and pyruvate kinase (PyPK). Meanwhile the glycogen content also declined under AICAR treatment. These results collectively suggested that PyAMPKα was involved in the high temperature stress response of scallops by enhancing glycolysis pathway of glycogen. These results would be helpful for understanding the functions of PyAMPKα in maintaining energy homeostasis under high temperature stress in scallops.

Effects of dietary melatonin on growth performance, antioxidant capacity, and nonspecific immunity in crayfish, Cherax destructor

Melatonin (MT) is an indole hormone widely found in plants and animals. Many studies have shown that MT promotes the growth and immunity of mammals, fish, and crabs. However, the effect on commercial crayfish has not been demonstrated. The purpose of this study was to evaluate the effects of dietary MT on growth performance and innate immunity of Cherax destructor from three aspects of individual level, biochemical level, and molecular level after 8 weeks of culture. In this study, we found that MT supplementation increased weight gain rate, specific growth rate, and digestive enzyme activity in C. destructor compared to the control group. Dietary MT not only promoted the activity of T-AOC, SOD, and GR, increased the content of GSH, and decreased the content of MDA in the hepatopancreas, but also increased the content of hemocyanin and copper ions and AKP activity in hemolymph. Gene expression results showed that MT supplementation at appropriate doses increased the expression of cell cycle-regulated genes (CDK, CKI, IGF, and HGF) and non-specific immune genes (TRXR, HSP60, and HSP70). In conclusion, our study showed that adding MT to the diet improved growth performance, enhanced the antioxidant capacity of hepatopancreas, and immune parameters of hemolymph in C. destructor. In addition, our results showed that the optimal dietary supplementation dose of MT in C. destructor is 75-81 mg/kg.

An ATP-binding cassette transporter G2 (CgABCG2) regulates the haemocyte proliferation by modulating the G1/S phase transition of cell cycle in oyster Crassostrea gigas

ATP-binding cassette transporter G2 (ABCG2) is a half-transporter of the G subfamily in ATP-binding cassette transporters (ABC transporter), which is involved in the regulation of multidrug-resistant, cell cycle, and cell proliferation. In the present study, a homologue of ABCG2 (named as CgABCG2) with the conserved AAA domain and ABC2 membrane domain was identified from the Pacific oyster Crassostrea gigas. The open reading frame (ORF) of CgABCG2 was of 1956 bp encoding a predicted polypeptide of 652 amino acids, which shared 56.7%-65.7% sequence similarities with previously identified ABCG2s from other animals. The mRNA transcripts of CgABCG2 were detected in all the tested tissues with higher expression levels in gonad and haemocytes (19.31-fold and 11.23-fold of that in adductor muscle respectively, p < 0.05). CgABCG2 was mainly distributed on the cell membrane of the haemocytes with a partial distribution in the cytoplasm and nucleus. After Vibrio splendidus stimulation, the mRNA expression level of CgABCG2 in haemocytes was significantly up-regulated at 3 h and 6 h, which was 5.22-fold and 8.60-fold (p < 0.05) of that in control, respectively. After the expression of CgABCG2 was interfered by RNAi, the number of cells with EdU positive signals was reduced in both haemocytes and the potential hematopoietic sites. And the mRNA expression level of CgPCNA, CgGATA3, CgRunx, CgSCL and CgC-kit decreased significantly (p < 0.05), which were about 0.66-, 0.37-, 0.32-, 0.50-, and 0.50-fold of that in the negative control group, respectively. While the mRNA expression level of CgCDK2 increased significantly (1.84-fold to that in control, p < 0.05) and that of stem cell-related factor CgSOX2 did not change significantly in the si-CgABCG2 oysters. Moreover, the cell cycle of haemocytes was detected by flow cytometry, which was arrested at G0/G1 phase in the si-CgABCG2 oysters. All the results collectively suggested that CgABCG2 might involve the proliferation of haemocytes by regulating the expression of haematopoiesis related transcription factors and the G1/S phase transition of the cell cycle in oyster C. gigas.

The expression profile of a multi-stress inducible transient receptor potential vanilloid 4 (TRPV4) in Pacific oyster Crassostrea gigas

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CgTRPV4 with typical structural characteristics was indentified from Crassostrea gigas.

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CgTRPV4 was located in both endoplasmic reticulum and cytoplasmic membrane of oyster haemocytes.

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CgTRPV4 mRNA was ubiquitously expressed with the highest level in gill.

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The expression of CgTRPV4 mRNA was significantly up-regulated after high temperature stress at 30°C or V. splendidus stimulation.

Transient receptor potential vanilloid 4 (TRPV4) is one of the major non-selective cation channel proteins, which plays a crucial role in sensing biotic and abiotic stresses, such as pathogen infection, temperature, mechanical pressure and osmotic pressure changes by regulating Ca²⁺ homeostasis. In the present study, a TRPV4 homologue was identified in Pacific oyster Crassostrea gigas, designated as CgTRPV4. The open reading frame (ORF) of CgTRPV4 was of 2298 bp encoding a putative polypeptide of 765 amino acid residues with three typical ankyrin domains and six conserved transmembrane domains of TRPV4 subfamily proteins, as well as multiple N-glycosylation sites, cAMP- and cGMP-dependent protein kinase phosphorylation sites, protein kinase C phosphorylation sites, casein kinase II phosphorylation sites, and prokaryotic membrane lipoprotein lipid attachment site. The deduced amino acid sequence of CgTRPV4 shared 20.5%-26.2% similarity with TRPV4s from other species. During the early ontogenesis stages of oyster, the mRNA transcripts of CgTRPV4 were detectable in all the stages with the highest expression level in fertilized eggs and the lowest in D-hinged larvae. In adult oyster, the CgTRPV4 mRNA could be detected in all the examined tissues, including gill, hepatopancreas, adductor muscle, labial palp, mantle and haemocyte, with the highest expression level in gill (45.08-fold of that in hepatopancreas, p < 0.05). In immunocytochemical assay, the CgTRPV4 positive signals were distributed in both endoplasmic reticulum and cytoplasmic membrane of oyster haemocytes. The mRNA expression of CgTRPV4 in gill was significantly up-regulated after high temperature stress at 30°C (p < 0.05) and after Vibrio splendidus stimulation (p < 0.05). These results indicated that CgTRPV4 was a classical member of TRPV4 family in oyster, which was induced by either biotic or abiotic stimulations and involved in mediating the stress response of oysters.

MEK homologue is involved in immune response by regulating antimicrobial peptides expression in Chinese mitten crab Eriocheir sinensis

MEK activates the phosphorylation of downstream molecules involved in various immune responses. In this study, an MEK homologue gene in Chinese mitten crab Eriocheir sinensis (designated as EsMEK) was investigated. EsMEK mRNA was constitutively expressed in all tissues with higher expression in hepatopancreas, hemocytes, and gills. EsMEK protein was mainly localized in the cytoplasm. Lipopolysaccharide (LPS) and Aeromonas hydrophila challenge significantly increased the mRNA levels of EsMEK in hemocytes. In addition, the mRNA expression level of some antimicrobial peptides (AMPs), including EsWAP, EsDWD1, and EsALF decreased significantly due to the inhibition of EsMEK by specific dsRNA in LPS-challenged crabs. Downstream pathway analysis revealed that the phosphorylation of EsERK decreased prominently after EsMEK inhibition. These results suggested that EsMEK played an important role in regulating the expression of antimicrobial peptides in E. sinensis through MEK-ERK pathway.

Blood cell formation in crustaceans

In crustacean animals the hemocytes are key players in immunity and of crucial importance for the health of the animals. Hemocytes are mainly produced in the hematopoietic tissue and from there released into the circulation where they finally mature. In this review we summarize the latest findings about crustacean hemocyte formation. The role of the extracellular matrix and crosslinking enzyme transglutaminase is discussed. Moreover, important growth factors, transcriptional regulation and recent findings about inducers of hematopoiesis are covered. Finally, we discuss the use of different markers for classification of crustacean hemocytes.

Effects of nanoplastic exposure on the growth performance and molecular characterization of growth-associated genes in juvenile Macrobrachium nipponense

Nanoplastic pollution has become a major issue in the aquatic environment while there are few studies examined the effects of nanoplastic exposure on crustaceans. To investigate this issue, we exposed juvenile shrimp, Macrobrachium nipponense to 75 nm polystyrene with 0, 5, 10, 20 and 40 mg/L nanoplastics concentrations for 28 days. The effects of nanoplastic exposure on the microstructure of the hepatopancreas, digestive enzyme activity and expression of growth-related genes were studied. The results showed that (1) adverse effects on the hepatopancreas were positively correlated with nanoplastic concentration; (David et al.) the activity of lipase, trypsin and pepsin was initially promoted and then inhibited with increasing nanoplastic concentration, whereas the activity of amylase was not significantly affected; (3) molting-associated genes were initially promoted and then inhibited with increasing nanoplastic concentration; (4) CDK2 gene was first cloned and molecular characteristics were analyzed. (5) polystyrene nanoplastics concentration >10 mg/L showed inhibition effect on CDK2 expression. These results indicated that nanoplastics affect the growth, digestive enzyme activity, hepatopancreas function and growth-related gene expression. Capsule: Our results identified the effects of nanoplastics on the growth performance of Macrobrachium nipponense in terms of digestion and molting.

Clinicopathological significance and prognostic value of P27 expression in gastric cancer patients: a meta-analysis

Loss of P27 expression correlates with clinical progression in a variety of human cancers. However, the correlation between P27 expression and gastric cancer remains controversial. In this meta-analysis, we performed an electronic search based on six databases to select a sufficient number of studies. Pooled hazard ratio (HR) was used as estimates to investigate the association between P27 expression and prognosis of patients with gastric cancer. We identified 19 studies with 2387 gastric cancer patients, ranging between 50 and 316 samples per study. Q and I2 tests demonstrated that the homogeneity among 19 studies (I2 = 47%, P = 0.0004), thus we applied a fixed-effects model to calculate the pooled HR of P27expression and overall survival (OS) of gastric cancer patients was 0.68, and 95% confidence interval (CI) was 0.60-0.78. Next, we conducted a subgroup meta-analysis and found that patients with low P27 expression in Asians (HR = 0.69, 95% CI: 0.58-0.82) and non-Asians (HR = 0.57, 95% CI: 0.41-0.79) had poor prognosis. In addition, we found the publication bias results of OS in the final included 19 studies showed that this funnel plot presented incomplete symmetry, and then removed three literatures with larger HRs bias, and found that the remaining 16 literatures were homogeneity (I2 = 0%, P = 0.47), the pooled HR was 0.52 with 95% CI of 0.43-0.62, and the publication bias disappeared. These results suggested a strong association between P27 underexpression and poorer prognosis of gastric cancer in patients. P27 may be a tumor suppressor for predicting survival outcome of gastric cancer patients.

The Elevated Expressions of Anti-lipopolysaccharide Factors After Priming Stimulation Confer Lastingly Humoral Protection in Crab Eriocheir sinensis

Evidence of immune memory in invertebrates (immune priming) has accumulated in various organisms, and both cellular and humoral immune reactions are speculated to be involved in immune priming. However, there is a lack of understanding of the molecular mechanisms involved. In the present study, the protective effect of primed haemolymph was further validated by the increased survival rate of naïve crabs receiving a transfusion of primed haemolymph. By proteomic analysis, there were 474 proteins identified from the primed haemolymph, and most of them were functionally annotated in transport and metabolism classes. A total of 70 proteins were found to be differentially expressed in haemolymph at 12 hours and 7 days after priming stimulation with Aeromonas hydrophila, among which anti-lipopolysaccharide factor 1 (EsALF-1) and 3 (EsALF-3) were identified as the most significant (p < 0.05). After being challenged with A. hydrophila, EsALF-1 and EsALF-3 were highly expressed at both mRNA (in haemocytes) and protein (in haemolymph) levels compared with blank crabs, and the mRNA expressions of components in the EsTLR1-EsMyd88-EsPelle-EsALF pathway also increased significantly (p < 0.05). The EsALF-3 and EsMyd88 were even significantly higher expressed in response to the second A. hydrophila challenge, but their expressions all decreased (p < 0.05) when EsTLR1 was knocked down by RNAi. After the naïve crabs received an injection with the recombinant protein of EsALF-1 (rEsALF-1) or EsALF-3 (rEsALF-3), their survival rate increased significantly (p < 0.05) upon A. hydrophila stimulation. In contrast, the survival rate of the primed crabs reduced significantly (p < 0.05) after they received an injection with the antibody of EsALF-1 or EsALF-3. The enhanced expressions of EsALF-1 and EsALF-3 after A. hydrophilap riming stimulation could sustain for four weeks. All the results suggested that the EsTLR1-mediated productions of EsALF-1 and EsALF-3 in haemolymph played an indispensable role in the month-long humoral immune protection induced by A. hydrophila, which provides solid evidence of immune priming in crabs and a valuable reference for further understanding immune memory in invertebrates.

DNA binding protein CgIkaros-like regulates the proliferation of agranulocytes and granulocytes in oyster (Crassostrea gigas)

DNA-binding protein Ikaros is a major determinant of haematopoietic lineage, especially in the development, differentiation and proliferation of lymphocytes. In the present study, a Ikaros homologue (designed as CgIkaros-like) was identified and characterized as a vital determinant in the proliferation of haemocytes during haematopoiesis of Pacific oyster Crassostrea gigas. The complete coding sequence of CgIkaros-like was of 1329 bp encoding a predicted polypeptide of 442 amino acids with four ZnF regions, locating at the C-terminus and N-terminus respectively. The highest expression level of CgIkaros-like mRNA was found in gills, followed by haemocytes and gonad. The mRNA transcripts of CgIkaros-like could be detected in all the haemocytes with higher abundance in semi-granulocytes and agranulocytes. CgIkaros-like protein was localized in both of cytoplasm and nucleus with higher abundance in nucleus of oyster haemocytes. The mRNA and protein expression levels of agranulocyte marker CgCD9, granulocyte marker CgAATase, cell cycle related gene CgCDK2, Notch receptor CgNotch and Notch target gene CgHes1 all increased significantly (p < 0.05) after CgIkaros-like was interfered by siRNAs, which were about 27.33-, 2.63-, 24.34-, 4.45- and 6.08-fold of that in the siRNA-NC control group, respectively. While the transcripts of CgGATA3 and CgRunx did not change significantly after CgIkaros-like was interfered. These results demonstrated that CgIkaros-like functioned as a transcription factor combined with Notch pathway to mediate CgCDK2 and regulate the proliferation of oyster haemocytes.

The involvement of PyBeclin 1 and PyLC3 in regulating the activation of autophagy in scallop Patinopecten yessoensis after acute high temperature stress

Beclin 1 and LC3 are important autophagy regulation proteins involved in vesicle nucleation and extension stage, respectively. In the present study, a Beclin 1 and a LC3 were identified from Yesso scallop Patinopecten yessoensis (PyBeclin 1 and PyLC3). The open reading frame (ORF) of PyBeclin 1 was of 1335 bp encoding a putative polypeptide of 444 amino acid residues with an N-terminal BCL-2 homology 3 (BH3) domain, a central coiled-coil domain (CCD), and a C-terminal evolutionarily conserved domain (ECD). The ORF of PyLC3 was of 369 bp encoding a putative polypeptide of 122 amino acid residues with an APG12 domain. The deduced amino acid sequences of PyBeclin 1 and PyLC3 shared 31.92-74.09% and 68.38-79.50% identities with Beclin 1s and LC3s from other species, respectively. The mRNA transcripts of PyBeclin 1 and PyLC3 were found to be expressed in all the examined tissues, including adductor muscle, gonad, gill, haemocytes and mantle, with the highest expression level in gill and haemocytes. The mRNA expression level of PyBeclin 1 in haemocytes increased significantly at 1, 3, 6, 12 and 24 h (2.98-4.07 fold of that in the Blank group, p < 0.05), and returned to normal level at 48 h after acute high temperature stress at 25 °C. Unlike PyBeclin 1, the mRNA transcripts of PyLC3 in haemocytes were significantly up-regulated at1, 3, 6 and 12 h (1.80-2.54 fold of that in the Blank group, p < 0.05), then decreased to blank level at 24 h (p > 0.05), and increased significantly again at 48 h (3.70 fold of that in the Blank group, p < 0.05) after high temperature. PyBeclin 1 and PyLC3 were mainly located in the cytoplasm and a small amount in the nucleus with few puncta, and the numbers of PyBeclin 1 and PyLC3 puncta increased at 3 h after acute high temperature stress. The LC3-II levels in gill and haemocytes were significantly up-regulated at 1 h and 3 h after acute high temperature stress. These results collectively suggested that PyBeclin 1 and PyLC3 were conserved members of Beclin 1 and LC3 family in scallops, and involved in regulating the activation of autophagy in scallops after acute high temperature stress.

A novel nuclear factor Akirin regulating the expression of antimicrobial peptides in Chinese mitten crab Eriocheir sinensis

Akirin, a recently discovered nuclear factor, participates in regulating various processes, including cell proliferation and differentiation, embryonic development, and immunity. In the present study, a novel Akirin was identified from Chinese mitten crab Eriocheir sinensis (designated as EsAkirin), and its primary functions in regulating antimicrobial peptides were explored. The open reading frame of EsAkirin was of 615 bp, encoding a polypeptide of 204 amino acid residues. The deduced amino acid sequence of EsAkirin shared high similarities ranging from 44.1% to 89.2% with other Akirins. In the phylogenetic tree, EsAkirin was firstly clustered with Akirins from shrimp and then assigned into the invertebrate branch. The mRNA transcripts of EsAkirin were constitutively expressed in all the tested tissues, with the highest expression level (5.07-fold compared to the stomach, p < 0.01) in hepatopancreas. The mRNA expression of EsAkirin in hemocytes was significantly increased at 6 h, and reached the maximum level at 24 h post stimulations with either lipopolysaccharide (LPS) (5.04-fold, p < 0.01) or Aeromonas hydrophila (3.10-fold, p < 0.01). After the injection of EsAkirin-dsRNA, the mRNA expressions of EsALF2, EsLYZ, EsCrus2 and EsDWD1 were significantly decreased (p < 0.01) upon LPS stimulation. EsAkirin protein was prominently distributed in the nucleus of E. sinensis hemocytes after LPS and A. hydrophila stimulations. The relative luciferase reporter system analysis revealed that the activity of nuclear factor-κB was significantly up-regulated (2.64-fold, p < 0.01) in human embryonic kidney (HEK293T) cells after the over-expression of EsAkirin. Collectively, these results suggested that EsAkirin might play an important role in the immune responses of E. sinensis by regulating the expression of antimicrobial peptides.

Beclin-1 is involved in the regulation of antimicrobial peptides expression in Chinese mitten crab Eriocheir sinensis

Beclin-1, the mammalian ortholog of yeast Atg6, plays essential roles in the regulation of various processes, including autophagy, apoptosis, embryonic development and immune responses in vertebrates. However, the information about Beclin-1 in invertebrates especially in crustaceans is still very limited. In the present study, a novel Beclin-1 (designated as EsBeclin-1) was identified from Chinese mitten crab Eriocheir sinensis. The open reading frame of EsBeclin-1 cDNA was of 1,275 bp, encoding a typical APG6 domain. The deduced amino acid sequence of EsBeclin-1 shared high similarity ranging from 42.9% to 63.6% with the previously identified Beclins. In the phylogenetic tree, EsBeclin-1 was firstly clustered with Drosophila melanogaster Atg6 and then assigned into the branch of invertebrate Beclin-1. The mRNA transcripts of EsBeclin-1 were highly expressed in hepatopancreas, hemocytes and gill. After lipopolysaccharide (LPS) and Aeromonas hydrophila stimulations, the relative mRNA expression of EsBeclin-1 in hemocytes was significantly increased from 3 to 24 h with the peak level of 4.70-fold (p < 0.01) and 2.91-fold (p < 0.01) at 6 h, respectively. EsBeclin-1 protein was diffusely distributed in the cytoplasm of crab hemocytes under normal conditions, whereas it displayed predominantly punctuate distribution after LPS stimulation. After EsBeclin-1 was interfered with specific EsBeclin-1-dsRNA, the mRNA transcripts of some antimicrobial peptides, including EsALF2, EsLYZ, EsCrus and EsCrus2 in crab hemocytes were significantly decreased at 6 h post LPS stimulation. These results implicated that EsBeclin-1 played a role in regulating the antimicrobial peptides expressions in the immune responses of E. sinensis.

Cyclin-dependent kinase 2 (Cdk-2) from the White shrimp Litopenaeus vannamei: Molecular characterization and tissue-specific expression during hypoxia and reoxygenation

The cell cycle comprises a series of steps necessary for cell growth until cell division. The participation of proteins responsible for cell cycle regulation, known as cyclin dependent kinases or Cdks, is necessary for cycle progression. Cyclin dependent kinase 2 (Cdk-2) is one of the most studied Cdks. This kinase regulates the passage through the G1/S phase and is involved in DNA replication in the S phase. Cdks have been extensively studied in mammals, but there is little information about these proteins in crustaceans. In the present work, the nucleotide and amino acid sequence of Cdk-2 from the white shrimp (Cdk-2) and its expression during hypoxia and reoxygenation are reported. Cdk-2 is a highly conserved protein and contains the serine/threonine catalytic domain, an ATP binding site and the PSTAIRE sequence. The predicted Cdk-2 structure showed the two-lobed structure characteristic of kinases. Expression of Cdk-2 was detected in hepatopancreas, gills and muscle, with hepatopancreas having the highest expression during normoxic conditions. Cdk-2 expression was significantly induced after hypoxia for 24 h in muscle cells, but in hypoxia exposure for 24 followed by 1 h of reoxygenation, the expression levels returned to the levels found in normoxic conditions, suggesting induction of cell cycle progression in muscular cells during hypoxia. No significant changes in expression of Cdk-2 were detected in these conditions in hepatopancreas and gills.

A serotonin receptor (Cg5-HTR-1) mediating immune response in oyster Crassostrea gigas

Serotonin receptors, including ligand-gated ion channel (LGICs) and G protein-coupled receptors (GPCR), play vital roles in modulating physiological processes and immunoreaction. In the present study, a homologue of serotonin (5-HT) receptor was identified from oyster Crassostrea gigas (designated Cg5-HTR-1). Its open reading frame (ORF) was of 1239 bp, encoding a polypeptide of 412 amino acids with a seven transmembrane region. Cg5-HTR-1 shared high similarity with the 5-HTRs from other animals. The cAMP contents in HEK293T cells decreased significantly after Cg5-HTR-1 transfection and 5-HT incubation (p < .05), while blocking Cg5-HTR-1 with specific receptor antagonist reversed this downtrend. The intracellular Ca²⁺ concentrations increased significantly (p < .05) after cell transfection and 5-HT incubation, and the antagonist treatment also arrested this process. Cg5-HTR-1 transcripts were widely distributed in various tissues, with the highest level in hepatopancreas and lowest level in mantle and gill. The mRNA expression of Cg5-HTR-1 in hemocyte increased significantly after lipopolysaccharide (LPS) stimulation and reached the peak level (6.47-fold, p < .05) at 6 h post treatment. The inhibition of Cg5-HTR-1 significantly reduced the expression of tumor necrosis factor (TNF) mRNA in hemocyte, down-regulated the superoxide dismutase (SOD) activity in serum, and induced the apoptosis of hemocyte (p < .05). These results suggested that Cg5-HTR-1 was a novel member of 5-HT₁ receptor family and it mediated serotonergic immunomodulation on both cellular and humoral immune responses.