TMT-Based Quantitative Proteomic Analysis Reveals the Key Role of Cell Proliferation and Apoptosis in Intestine Regeneration of Apostichopus japonicus

Sea cucumbers are widely known for their powerful regenerative abilities, which allow them to regenerate a complete digestive tract within a relatively short time following injury or autotomy. Recently, even though the histological changes and cellular events in the processes of intestinal regeneration have been extensively studied, the molecular machinery behind this faculty remains unclear. In this study, tandem mass tag (TMT)-based quantitation was utilized to investigate protein abundance changes during the process of intestine regeneration. Approximately 538, 445, 397, 1012, and 966 differential proteins (DEPs) were detected (p < 0.05) between the normal and 2, 7, 12, 20, and 28 dpe stages, respectively. These DEPs also mainly focus on pathways of cell proliferation and apoptosis, which were further validated by 5-Ethynyl-2'-deoxyuridine (EdU) or Tunel-based flow cytometry assay. These findings provide a reference for a comprehensive understanding of the regulatory mechanisms of various stages of intestinal regeneration and provide a foundation for subsequent research on changes in cell fate in echinoderms.

Dietary tryptophan decreases the impacts of seawater temperature changes on behavior and gut health of the sea cucumber Apostichopus japonicus

Seawater temperature change is an important concern for seed production and pond culture of sea cucumbers. The present study found that tentacle activity frequency was significantly lower in sea cucumbers exposed to continuous and rapid temperature increases than that of those at ambient temperature. Feeding behavior directly determines food intake, and further affects physiology and growth efficiency of sea cucumbers. This means that the decline in feeding caused by continuous and rapid temperature increases needs to be addressed in sea cucumber aquaculture. However, a sudden temperature change of 5 °C had no significant effect on behaviors of sea cucumbers. This indicates that continuous temperature increases, rather than a sudden increase, result in behavioral impacts on sea cucumbers. Therefore, we recommend aqua-farmers reduce the feeding amount for sea cucumbers during continuous and rapid temperature increases. In the present study, feeding behavior was significantly higher in sea cucumbers fed with 3% dietary tryptophan than that of those fed with 0% and 5% dietary tryptophan. This indicates that 3% dietary tryptophan increases the food intake of sea cucumbers, and mitigates the feeding decline caused by continuous and rapid temperature increase. This indicates that tryptophan has the potential to promote the feeding of sea cucumbers in seed production and pond culture. Adhesion capacity of sea cucumbers fed with 5% dietary tryptophan was significantly higher than that of individuals fed with 0% and 3% dietary tryptophan. This suggests that dietary tryptophan increases the feeding of sea cucumbers exposed to continuous and rapid temperature increases in pond culture and seed production. In addition, this study found that sea cucumbers fed with 3% dietary tryptophan had higher intestinal colony richness under the continuously rapid temperature change. The present study provides an effective method to improve adhesion behavior and to alleviate the impacts on feeding behavior for seed production and pond culture of sea cucumbers exposed to continuous and rapid temperature increases.

Chemical substances and their activities in sea cucumber Apostichopus japonicus: A review

Apostichopus japonicus, also known as Stichopus japonicus, with medicinal and food homologous figures, is a globally recognized precious ingredient with extremely high nutritional value. There is no relevant review available through literature search, so this article selects the research articles through the keywords "sea cucumber" and "Apostichopus japonicus (Stichopus japonicus)" in six professional databases, such as Wiley, PubMed, ScienceDirect, ACS, Springer, and Web of Science, from 2000 to the present, summarizing the extraction, isolation, and purification methods for the four major categories (polysaccharides, proteins and peptides, saponins, and other components) of the A. japonicus chemical substances and 10 effective biological activities of A. japonicus. Included are anticoagulation, anticancer/antitumor activities, hematopoiesis, regulation of gut microbiota, and immune regulatory activities that correspond to traditional efficacy. Literature support is provided for the development of medicines and functional foods and related aspects that play a leading role in future directions.

Sulfide causes histological damage, oxidative stress, metabolic disorders and gut microbiota dysbiosis in juvenile sea cucumber Apostichopus japonicus Selenka

Sulfide is a common harmful substance in sediments, with an especially high risk for deposit feeder organisms. The sea cucumber Apostichopus japonicus is a typical benthic feeder, and its intestine is the first line of defense and serves as a crucial barrier function. In this study, histological, physiological, gut microbiota, and metabolomic analyses were performed to explore the toxic response in the intestine of juvenile A. japonicus exposed to 0, 0.8, and 1.6 mg/L sulfide stress for 96 h. The results revealed sulfide-induced intestinal inflammatory symptoms and oxidative stress. Moreover, gut bacterial composition was observed after sulfide exposure, with an increase in Proteobacteria and a decrease in Cyanobacteria and Planctomycetes. Specifically, sulfide increased a set of sulfide-removing bacteria and opportunistic pathogens while decreasing several putative beneficial substance-producing bacteria. The metabolomic analysis indicated that sulfide also disturbed metabolic homeostasis, especially lipid and energy metabolism, in intestine. Interestingly, several intestinal bacteria were further identified to be significantly correlated with metabolic changes; for example, the decreased abundance levels of Bacillus, Corynebacterium, and Psychromonas were positively correlated with important energy metabolites, including maleic acid, farnesyl pyrophosphate, thiamine, butynoic acid, and deoxycholic acid. Thus, our research provides new insights into the mechanisms associated with the intestinal metabolic and microbiota response involved in sulfide stress adaptation strategies of juvenile A. japonicus.

Heat stress and evisceration caused lipid metabolism and neural transduction changes in sea cucumber: Evidence from metabolomics

When encountering adverse environmental conditions, some holothurians can eject their internal organs in a process called evisceration. As global warming intensified, eviscerated and intact sea cucumbers both experience heat stress, but how they performed was uncertain. We constructed 24 metabolomics profiles to reveal the metabolite changes of eviscerated and intact sea cucumbers under normal and high temperature conditions, respectively. Carboxylic acids and fatty acyls were the most abundant metabolic categories in evisceration and heat stress treatments, respectively. Neural transduction was involved in sea cucumber evisceration and stress response, and the commonly enriched pathway was "neuroactive ligand-receptor interaction". Lipid metabolism in eviscerated sea cucumbers differed from those of intact individuals and was more seriously affected by heat stress. Choline is a key metabolite for revealing the evisceration mechanism. Our results contribute to understanding the mechanisms of evisceration in sea cucumbers, and how sea cucumbers might respond to increasingly warming ocean conditions.

The exogenous autophagy inducement alleviated the sea cucumber (Stichopus japonicus) autolysis with exposure to stress stimuli of ultraviolet light

BACKGROUND

Autolysis is the most important restrictive factor for the live sea cucumber trade and commercial transportation. Thus, it is essential to investigate the mechanism of autolysis activation or deactivation in the sea cucumber. In this study, monodansylcadaverine staining and Western blotting experiment methods indicated the implication of autophagy in the ultraviolet (UV) exposed sea cucumbers. The health condition was observed after the sea cucumbers (Stichopus japonicus) were gastric perfusion with autophagic inhibitor (3-methyladenine) or inducer (rapamycin) and exposure to UV light for half an hour.

RESULTS

The protein expressions of LC3-II and Atg5 appeared immediately after UV exposure and then vanished 1 h later. The autophagosome formation in coelomic fluid cells confirmed the autophagy appearance pattern of LC3-II and Atg5. The sea cucumber individuals maintained the health condition during the entire event of autophagy. The autophagic inhibitor along with UV exposure contributed to sea cucumber's swollen intestinal tissues, but the autophagic inducer functioned to alleviate and neutralize the UV effect.

CONCLUSIONS

The autophagy procedure analysis demonstrated that autophagy plays a role to maintain the health condition of sea cucumber during autolysis inducement. The autolysis of sea cucumber can be alleviated or postponed by the exogenous autophagy inducer and this finding would benefit the live sea cucumber transportation. © 2021 Society of Chemical Industry.

Transcriptomic responses to air exposure stress in coelomocytes of the sea cucumber, Apostichopus japonicus

During rearing in hatcheries and transportation to restocking sites, sea cucumbers are often exposed to air for several hours, which may depress their non-specific immunity and lead to mass mortality. We performed transcriptome analysis of Apostichopus japonicus coelomocytes after air exposure to identify stress-related genes and pathways. After exposure to air for 1 h, individuals were re-submerged in aerated seawater and coelomocytes were collected at 0, 1, 4, and 16 h (B, H1, H4, and H16, respectively). We identified 6148 differentially expressed genes, of which 3216 were upregulated and 2932 were downregulated. Many genes involved in the immune response, antioxidant defense, and apoptosis were highly induced in response to air exposure. Enrichment analysis of Gene Ontology terms showed that the most abundant terms in the biological process category were oxidation-reduction process, protein folding and phosphorylation, and receptor-mediated endocytosis for the comparison of H1 vs. B, H4 vs. H1, and H16 vs. H4, respectively. Kyoto Eecyclopedia of Genes and Genomes enrichment analysis showed that six pathways related to the metabolism of proteins, fats, and carbohydrates were shared among the three comparisons. These results indicated that sea cucumbers regulate the expression of genes related to the antioxidant system and energy metabolism to resist the negative effects of air exposure stress. These findings may be applied to optimize juvenile sea cucumber production, and facilitate molecular marker-assisted selective breeding of an anoxia-resistant strain.

Distinct microbiota assembly mechanisms revealed in different reconstruction stages during gut regeneration in the sea cucumber Apostichopus japonicus

Apostichopus japonicus is a useful model for studying organ regeneration, and the gut microbiota is important for host organ regeneration. However, the reconstruction process and the mechanisms of gut microbiota assembly during gut regeneration in sea cucumbers have not been well studied. In the present study, gut regeneration was induced (via evisceration) in A. japonicus, and gut immune responses and bacterial diversity were investigated to reveal gut microbiota assembly and its possible mechanisms during gut regeneration. The results revealed that bacterial community reconstruction involved two stages with distinct assembly mechanisms, where the reconstructed community was initiated from the bacterial consortium in the residual digestive tract and tended to form a novel microbiota in the later stage of reconstruction. Together, the results of immunoenzyme assays, community phylogenetic analysis, and source tracking suggested that the host deterministic process was stronger in the initial stage than in the later stage. The bacterial interactions that occurred were significantly different between the two stages. Positive interactions dominated in the initial stage, while more complex and competitive interactions developed in the later stage. Such a dynamic bacterial community could provide the host with energetic and immune benefits that promote gut regeneration and functional recovery. The results of the present study provide insights into the processes and mechanisms of gut microbiota assembly during intestinal regeneration that are valuable for understanding gut regeneration mechanisms mediated by the microbiota.

Infective prey leads to a partial role reversal in a predator-prey interaction

An infective prey has the potential to infect, kill and consume its predator. Such a prey-predator relationship fundamentally differs from the predator-prey interaction because the prey can directly profit from the predator as a growth resource. Here we present a population dynamics model of partial role reversal in the predator-prey interaction of two species, the bottom dwelling marine deposit feeder sea cucumber Apostichopus japonicus and an important food source for the sea cucumber but potentially infective bacterium Vibrio splendidus. We analyse the effects of different parameters, e.g. infectivity and grazing rate, on the population sizes. We show that relative population sizes of the sea cucumber and V. Splendidus may switch with increasing infectivity. We also show that in the partial role reversal interaction the infective prey may benefit from the presence of the predator such that the population size may exceed the value of the carrying capacity of the prey in the absence of the predator. We also analysed the conditions for species extinction. The extinction of the prey, V. splendidus, may occur when its growth rate is low, or in the absence of infectivity. The extinction of the predator, A. japonicus, may follow if either the infectivity of the prey is high or a moderately infective prey is abundant. We conclude that partial role reversal is an undervalued subject in predator-prey studies.

Combined Effects of Elevated Temperature and Crude Oil Pollution on Oxidative Stress and Apoptosis in Sea Cucumber (Apostichopus japonicus, Selenka)

Currently, global climate change and oil pollution are two main environmental concerns for sea cucumber (Apostichopus japonicus) aquaculture. However, no study has been conducted on the combined effects of elevated temperature and oil pollution on sea cucumber. Therefore, in the present study, we treated sea cucumber with elevated temperature (26 °C) alone, water-accommodated fractions (WAF) of Oman crude oil at an optimal temperature of 16 °C, and Oman crude oil WAF at an elevated temperature of 26 °C for 24 h. Results showed that reactive oxygen species (ROS) level and total antioxidant capacity in WAF at 26 °C treatment were higher than that in WAF at 16 °C treatment, as evidenced by 6.03- and 1.31-fold-higher values, respectively. Oxidative damage assessments manifested that WAF at 26 °C treatment caused much severer oxidative damage of the biomacromolecules (including DNA, proteins, and lipids) than 26 °C or WAF at 16 °C treatments did. Moreover, compared to 26 °C or WAF at 16 °C treatments, WAF at 26 °C treatment induced a significant increase in cellular apoptosis by detecting the caspase-3 activity. Our results revealed that co-exposure to elevated temperature and crude oil could simulate higher ROS levels and subsequently cause much severer oxidative damage and cellular apoptosis than crude oil alone on sea cucumber.

Effects of aerial exposure on oxidative stress, antioxidant and non-specific immune responses of juvenile sea cucumber Apostichopus japonicus under low temperature

Desiccation is a commonly stressful situation experienced by sea cucumber during transportation without/less water. The present study was conducted to investigate the effects of aerial exposure on the survival, oxidative damage, antioxidant capacity, immune-related response and gene expression of Apostichopus japonicus at different low temperatures. After acclimation, sea cucumbers were randomly divided into 3 groups, which were exposed to 5 °C, 10 °C and 15 °C in the closed laboratory condition, respectively. Each group has three parallel replicates. During the experiment, coelomic fluid and respiratory tree of A. japonicus were sampled at the time points of 0, 3, 6, 12, 24 and 48 h post-desiccation for further analysis. The results showed that the survival rates of sea cucumber significantly decreased as time prolonged, and those of 5 °C at 6-48 h of desiccation were significantly higher than 15 °C. Most oxidative damage parameters (e.g., O₂^- production, MDA, LPO and PC contents) significant increased after 6-12 h of desiccation. Antioxidant enzyme activities and T-AOC in coelomic fluid firstly increased and then decreased during aerial exposure, indicating that sea cucumber could adjust antioxidant defense to reduce the concentrations of ROS and MDA as a strategy for protecting organisms from oxidative damage in the early stage (0-6 h) of desiccation. The relative expression levels of Hsp90 and Hsp70 mRNA in respiratory tree of sea cucumber exhibited similar rise-fall trends with antioxidant parameters, while immune enzyme activities of ACP, AKP, LSZ and T-NOS, and gene expression of TLR, Rel and p105 all significantly decreased as time prolonged. Overall, low temperature postponed the process of ROS formation and the depression of antioxidant and non-specific immune responses of sea cucumber within a certain extent, which implied that it might play a positive role in improvement of desiccation tolerance. This study not only contribute to better understand the adaption mechanisms of A. japonicus to desiccation stress, but also provide valuable information for sea cucumber culture and transportation.

The role of matrix metalloprotease (MMP) to the autolysis of sea cucumber (Stichopus japonicus)

BACKGROUND

Sea cucumber (Stichopus japonicus) is easy to autolysis in response to a variety of environmental and mechanical factors. In the current study, collagen fibres were extracted from fresh sea cucumber body wall and then incubated with endogenous matrix metalloprotease (MMP) of sea cucumber. Scanning electron microscopy (SEM), differential scanning calorimetry (DSC), chemical analysis and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE) analysis were utilized to demonstrate the changes in collagen fibres, collagen fibrils and collagen proteins. Moreover, a verification experiment was also carried out to confirm the contribution of MMP to the autolysis of sea cucumber.

RESULTS

Endogenous MMP caused complete depolymerization of collagen fibres into smaller collagen fibril bundles and collagen fibrils due to the fracture of proteoglycan interfibrillar bridges. Meanwhile, endogenous MMP also caused partial degradation of collagen fibrils by releasing soluble hydroxyproline and pyridinium cross-links. Furthermore, the treatment with MMP inhibitor (1,10-phenanthroline) prevented the autolysis of tissue blocks from S. japonicus dermis.

CONCLUSION

Endogenous MMP was the key enzyme in the autolysis of sea cucumber, while its action still focused on high-level structures of collagens especially collagen fibres. © 2019 Society of Chemical Industry.

Gender specific differences of immune competence in the sea cucumber Apostichopus japonicus before and after spawning

The gender differences of immunity have been elucidated in many vertebrates and invertebrates. However, the information of this difference was still not clear in the sea cucumber Apostichopus japonicus, which is one of the most valuable aquaculture species and susceptible to diseases caused by pathogen infection. In the present study, the transcriptome of coelomocytes from female and male A. japonicus before and after spawning was obtained by RNA-sequencing technology. A total of 4,538 and 8,248 differentially expressed genes were identified between female and male A. japonicus before and after spawning, respectively, indicating that the gender differences of gene expression profiles in A. japonicus were more remarkable after spawning. Further KEGG enrichment analyses were conducted for both male and female up-regulated genes before and after spawning. The results revealed that the capacity to kill pathogens in female A. japonicus might be more powerful than that in males no matter before and after spawning; the antioxidant ability in male A. japonicus was probably stronger than that in females after spawning; the complement system in male A. japonicus might be more effective than that in females after spawning; and the apoptosis was likely to be more serious in male A. japonicus before spawning. Moreover, we speculated that the fatty acid composition might be one of the inducements for gender specific immune differences of A. japonicus. Overall, the results of our study illustrated the global gender specific immune differences of A. japonicus and contributed to understanding of the molecular mechanisms underlying sea cucumber immune regulation.

VEGF-like protein from Apostichopus japonicus promotes cell proliferation and migration

Vascular endothelial growth factor (VEGF) is a key conservative regulator of inflammation response by promoting cell proliferation, migration, and vascular permeability. It also induces the release of inflammatory factors in vertebrates. We previously characterized NLR family pyrin domain containing 3 and HMGB3 homology in Apostichopus japonicus, providing the occurrence of inflammation in this species. However, to our knowledge, other inflammation-related molecules, such as VEGF, have rarely been investigated. In the present study, a novel VEGF homolog was identified from A. japonicus (designated as AjVEGF) by rapid amplification of cDNA ends. Full-length cDNA of AjVEGF was 3181 bp with a putative open reading frame of 1752 bp encoding 583 amino acid (aa) residue protein. Structural analysis revealed that AjVEGF processed characteristic VEGF domains of platelet-derived growth factor domain (132-232 aa) and CXC domain (223-270 aa). Multiple sequence alignment and phylogenetic analysis both supported that AjVEGF belongs to a new member of VEGF protein subfamily. Both Vibrio splendidus challenge in vivo and lipopolysaccharide stimulation in vitro could significantly upregulate mRNA expression of AjVEGF compared with the control group. Functional analysis indicated that recombinant AjVEGF promoted coelomocyte proliferation and migration not only in sea cucumber but also in human colorectal adenocarcinoma cells (HT29). This consistent function was also detected for human VEGFs. Taken together, these findings suggest that AjVEGF has a similar function of VEGF in higher animals and might serve as a candidate cytokine in sea cucumber inflammation.

Metabolome responses of the sea cucumber Apostichopus japonicus to multiple environmental stresses: Heat and hypoxia

Economically important marine organisms face severe environmental challenges, such as high temperature and low dissolved oxygen, from global climate change. Adverse environmental factors impact the survival and growth of economically important marine organisms, thereby negatively influencing the aquaculture industry. However, little is known about the responses of sea cucumbers to combined environmental co-stressors till now. In this study, ultra-performance liquid chromatography (UPLC) was utilized to obtain metabolic profiles of sea cucumbers. Changes in the concentrations of 84, 68, and 417 metabolites related to the responses of sea cucumbers to heat (26 °C), hypoxia (2 mg/L) and the combined stress, respectively, were observed and analyzed. Representative biomarkers were discussed in detail, including deltaline, fusarin C, halichondrin B and rapanone. The concentration of metabolites involved in the regulation of energy metabolism, including amino acid, carbohydrate and lipid metabolism were significantly changed, and the tricarboxylic acid (TCA)-cycle was significantly altered under heat plus hypoxia. We interpreted these changes partly as an adaptation mechanism in response to environmental stress. Based on the decreased accumulation of glutamine, we hypothesized that heat stress is the main factor that interferes with the process of glutamic acid-glutamine metabolism. The present study showed that combined environmental stressors have a more extensive impact on the metabolites of the respiratory tree in sea cucumbers than single stress. These results would facilitate further development of the sea cucumber as an echinoderm model to study mechanisms of response to adverse environments, as well as to help advance knowledge of the adaptation of marine organisms to global climate change.

Regulation of growth, intestinal microbiota, non-specific immune response and disease resistance of sea cucumber Apostichopus japonicus (Selenka) in biofloc systems

Bioflocs are not only a source of supplemental nutrition but also provide substantial probiotic bacteria and bioactive compounds, which play an important role in improving physiological health of aquatic organisms. A 60-day experiment was conducted to investigate the growth, intestinal microbiota, non-specific immune response and disease resistance of sea cucumber in biofloc systems with different carbon sources (glucose, sucrose and starch). Control (no biofloc) and three biofloc systems were set up, and each group has three replicates. The results showed that biofloc volume (BFV) and total suspended solids (TSS) increased in the sequences of glucose > sucrose > starch and green sea cucumber > white sea cucumber during the experiment. The highest specific growth rates (SGRs) were observed in biofloc system with glucose as carbon source, which also had relatively lower glucose, lactate and cortisol levels in coelomic fluid and higher glycogen content in muscle compared to other groups. There were significant increased Bacillus and Lactobacillus counts of sea cucumber intestine in biofloc systems, and the activities of superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPx) also showed obvious ascending trends. Significant increases in total coelomocytes counts (TCC), phagocytosis, respiratory burst, complement C3 content and lysozyme (LSZ) and acid phosphatase (ACP) activities of sea cucumber were all found in biofloc system (glucose). The expression patterns of most immune-related genes (i.e. Hsp90, Hsp70, c-type lectin (CL), toll-like receptor (TLR)) were up-regulated, suggesting the promotion of pathogen recognition ability and immune signaling pathways activation by biofloc. Furthermore, green and white sea cucumber had significantly higher survival rates in biofloc systems during the 14-day challenge test. In conclusion, biofloc technology could improve growth and physiological health of A. japonicus, by optimizing intestinal microbiota, strengthening antioxidant ability, enhancing non-specific immune response and disease resistance against pathogens, meanwhile glucose was recommended as optimal carbon source in biofloc system of sea cucumber culturing.

Dietary supplementation of biofloc influences growth performance, physiological stress, antioxidant status and immune response of juvenile sea cucumber Apostichopus japonicus (Selenka)

Bioflocs are rich in various probiotics and bioactive compounds, which play an important role in improving growth and health status of aquatic organisms. A 60-day experiment was conducted to investigate the effects of dietary supplementation of biofloc on growth performance, digestive enzyme activity, physiological stress, antioxidant status, expression of immune-related genes and disease resistance of sea cucumber Apostichopus japonicus. Juvenile sea cucumbers were fed five experimental diets containing graded levels of biofloc from 0% to 20% (referred as B0, B5, B10, B15 and B20, respectively). The results showed that the sea cucumbers at dietary supplementation levels of 10%-15% biofloc had significantly higher specific growth rate (SGR) compared to control group (diet B0). Digestive enzyme activity increased with the increasing of dietary biofloc level, while no significant difference was found between diets B15 and B20. Dietary supplementation of biofloc also had significant influences on physiological stress parameters except for lactate. There was no significant discrepancy in total coelomocytes counts (TCC) in coelomic fluid of sea cucumber between the treatments. Phagocytosis and respiratory burst of cellular immune at 15% and 20% biofloc levels were significantly higher than those of control group. Significant increases in superoxide dismutase (SOD), total nitric oxide synthase (T-NOS), lysozyme (LSZ), acid phosphatase (ACP) and alkaline phosphatase (AKP) activities of sea cucumber were found at highest dietary supplementation level of 20% biofloc. The expression patterns of immune-related genes (i.e., Hsp90, Hsp70, p105, Rel, NOS and LSZ) in tissues of sea cucumber were analyzed between the experimental diets, and a general trend of up-regulation was observed at higher biofloc levels. Furthermore, dietary 10%-20% biofloc significantly reduced cumulative mortality of sea cucumber after being challenged with Vibrio splendidus. In conclusion, dietary supplementation of biofloc could improve growth performance of A. japonicus, by increasing digestive enzyme activity, releasing physiological stress, enhancing immune response and disease resistance of sea cucumber. The suitable supplemental level of approximately 15% biofloc was recommended in the present study.

Establishment of lysozyme gene RNA interference systemand its involvement in salinity tolerance in sea cucumber (Apostichopus japonicus)

The lysozyme gene was silenced using RNA interference (RNAi) to analyze the function of lysozyme in sea cucumber under salt stress. The interfering efficiency of four lysozyme RNAi oligos ranged from 0.55 to 0.70. From the four oligos, p-miR-L245 was used for further interfering experiments because it had the best silencing efficiency. Peristomial film injection of p-miR-L245 (10 μg) was used for further interfering experiments. The lowest gene expression, determined by RT-PCR assay, in muscle, coelomic fluid, and parapodium occurred 48 h after p-miR-L245 injection, while that of body wall and tube foot was 96 h and 24 h, respectively. Lysozyme activity in muscle and body wall was significantly lower than the controls. The lowest lysozyme activity in muscle, body wall and parapodium, was found at 48, 72, and 48 h, respectively, which was consistent with the transcription expression of lysozyme. The lowest point of lysozyme activity was at 96 h in coelomic fluid and tube foot, which was laid behind lysozyme expression in transcription level. The expression profile of the lysozyme transcription level and lysozyme activity in the body wall and tube foot increased at 12 h after p-miR-L245 injection before the interference effect appeared. NKA gene expression was expressed at a high level in the positive control (PC) and negative control (NC) groups at 12, 24, and 48 h, while NKA was expressed at low levels in the lysozyme RNAi injection group at 12 and 24 h. The level of NKA gene expression recovered to the level of the PC and NC group at 48, 72, and 96 h after the lysozyme RNAi injection. NKCC1 gene expression was high in the PC and NC groups at 96 h, while the NKCC1 was expressed at a low level 96 h after lysozyme RNAi injection. The results suggest that lysozyme decay involves NKA and NKCC1 gene expression under salinity 18 psμ. The K⁺ and Cl^- concentration after lysozyme RNAi injection was lower than in the PC and NC group.

Effects of tussah immunoreactive substances on growth, immunity, disease resistance against Vibrio splendidus and gut microbiota profile of Apostichopus japonicus

Tussah immunoreactive substance (TIS) comprises a number of active chemicals with various bioactivities. The current study investigated the effects of these substances on the sea cucumber Apostichopus japonicus. The specific growth rate (SGR) of TIS-fed sea cucumbers was significantly enhanced, whereas no significant difference in SGR was observed between those soaked in antibiotics and those fed with basal diet only. TIS also improved the immune response of the animals when given at a dose of 1.0% or 2.0%, as shown by increased phagocytic, lysozyme, superoxide dismutase, alkaline phosphatase, acid phosphatase, and catalase activities following injection with live Vibrio splendidus. At a dose of 1.0% or 2.0%, TIS significantly enhanced the immune ability (P < 0.05) of the sea cucumbers, but except for lysozyme activity, other immune indices were reduced one day after the animals were injected with Vibrio splendidus. However, the values of these immune indexes were still significantly higher compared to those of the control groups (P < 0.05). Intestinal micro flora counts and high-throughput sequencing showed that dietary TIS could improve the amount of probiotic bacteria, yielding a 6-fold increase in Bacillus and 10-fold increase in Lactobacillus for sea cucumbers fed with 2.0% TIS diet compared to the control. Furthermore, TIS-containing diet also greatly reduced the number of harmful bacteria, with the number of Vibrio in sea cucumbers fed with 1%TIS diet decreased by 67% compared to the control. The results thus indicated that TIS increased the growth of sea cucumbers and enhanced their resistance to V. splendidus infection by improving the immunity of the animals. TIS also improved the gut microbiota profiles of the animals by increasing the probiotics and reducing the harmful bacteria within their guts.

Differential count and time-course analysis of the cellular composition of coelomocyte aggregate of the Japanese sea cucumber Apostichopus japonicus

Echinoderms have many types of coelomocytes, which have been known to form aggregates immediately after they are removed from the coelom. To assess the roles that each type of coelomocyte plays in aggregate formation, cellular components of coelomocyte aggregates of the Japanese sea cucumber, Apostichopus japonicus, were investigated. The coelomocytes were tentatively classified into 12 types based on May-Grunwald/Giemsa staining. After the coelom was incubated for 30 min or 6 h, the aggregates were disaggregated completely with 200 mM EDTA. Differential counts of the dissociated cells indicated that the largest component of the aggregates was amoebocytes (67.8%) and the second-largest component of the aggregates incubated 30 min was a type of basophilic granulocyte. In the 6h-incubated aggregates, the fraction of amoebocytes decreased to 59.0%, while that of lymphoid cells significantly increased, which suggests that lymphoid cells participate in late-stage aggregation. After 24-h incubation, only a portion of the aggregated cells could be disaggregated with EDTA. After 48 h, most of the cells could not be detached from the aggregates. Microscopy of frozen sections of the aggregates after 6-h incubation revealed that amoebocytes constructed a mesh-like structure to which other types of cells adhered. After 48 h, the borders of the cells and the intracellular granules were not recognizable. In time-lapse microscopy, the aggregates were observed to move on a glass slide, which suggests that aggregates can "crawl" on the intraluminal surface of the coelom toward, for example, injured regions in the body of the sea cucumber.

Bioenergetic trade-offs in the sea cucumber Apostichopus japonicus (Echinodermata: Holothuroidea) in response to CO2-driven ocean acidification

Ocean acidification (OA) caused by excessive CO2 is a potential ecological threat to marine organisms. The impacts of OA on echinoderms are well-documented, but there has been a strong bias towards sea urchins, and limited information is available on sea cucumbers. This work examined the effect of medium-term (60 days) exposure to three pH levels (pH 8.06, 7.72, and 7.41, covering present and future pH variability) on the bioenergetic responses of the sea cucumber, Apostichopus japonicus, an ecologically and economically important holothurian in Asian coasts. Results showed that the measured specific growth rate linearly decreased with decreased pH, leading to a 0.42 %·day(-1) decrease at pH 7.41 compared with that at pH 8.06. The impacts of pH on physiological energetics were variable: measured energy consumption and defecation rates linearly decreased with decreased pH, whereas maintenance energy in calculated respiration and excretion were not significantly affected. No shift in energy allocation pattern was observed in A. japonicus upon exposure to pH 7.72 compared with pH 8.06. However, a significant shift in energy budget occurred upon exposure to pH 7.41, leading to decreased energy intake and increased percentage of energy that was lost in feces, thereby resulting in a significantly lowered allocation into somatic growth. These findings indicate that adult A. japonicus is resilient to the OA scenario at the end of the twenty-first century, but further acidification may negatively influence the grazing capability and growth, thereby influencing its ecological functioning as an "ecosystem engineer" and potentially harming its culture output.

Regulation of dietary glutamine on the growth, intestinal function, immunity and antioxidant capacity of sea cucumber Apostichopus japonicus (Selenka)

The present study examined the effects of dietary glutamine (Gln) on the growth, intestinal function, immunity and antioxidant capacity of sea cucumber Apostichopus japonicus (Selenka). The specific growth rate, intestinal morphology, activity of digestive enzymes, activity and gene expression of lysozyme and antioxidative enzymes of the sea cucumbers were determined after feeding 5 experimental diets with additions of increasing levels of Gln (at 0%, 0.4%, 0.8%,1.2% and 1.6%, respectively) for 60 days. We discovered that the specific growth rate of the sea cucumbers in 0.4%, 0.8% and 1.2% groups increased 35.3%, 27.3% and 24.1%, respectively, compared to the control (0%) group with significant differences. Dietary Gln can improve the intestinal function of the sea cucumbers by increasing the activities of trypsin and lipase in the intestine and the villus height and villus density of the intestine, eventhough significant differences were not observed in some groups. 0.4%-0.8% of dietary Gln can significantly increase the activity of lysozyme (LSZ) in the coelomic fluid of the sea cucumbers. Significant improvements were observed on the SOD activity in coelomic fluid of the sea cucumbers fed diets supplemented with 0.4%-1.6% of Gln compared to the control group. Similarly, the CAT activity in coelomic fluid of the sea cucumbers significantly increased in 0.8%, 1.2% and 1.6% groups compared to the control and 0.4% groups. Change pattern of the activity of CAT was consistent with the change pattern of the expression of CAT gene, indicating the dietary Gln can up-regulate the expression of CAT gene and consequently promote the secretion of CAT. However, the down-regulation of the expression of SOD gene by dietary Gln were observed in almost all of the treatment groups, which is in contrast with the change pattern of the activity of SOD, indicating the negative feedback regulation of the secretion of SOD on the expression of SOD gene. In summary, the suitable supplementation levels of Gln in diets of sea cucumber A. japonicus are 0.4%-0.8%, based on the effectiveness of dietary Gln on the growth, intestinal function, immunity and antioxidant capacity of the sea cucumbers.

Effects of dietary Bacillus cereus G19, B. cereus BC-01, and Paracoccus marcusii DB11 supplementation on the growth, immune response, and expression of immune-related genes in coelomocytes and intestine of the sea cucumber (Apostichopus japonicus Selenka)

Probiotics have positive effects on the nutrient digestibility and absorption, immune responses, and growth of aquatic animals, including the sea cucumber (Apostichopus japonicus Selenka). A 60-day feeding trial was conducted to evaluate the effects of Bacillus cereus G19, B. cereus BC-01 and Paracoccus marcusii DB11 supplementation on the growth, immune response, and expression level of four immune-related genes (Aj-p105, Aj-p50, Aj-rel, and Aj-lys) in coelomocytes and the intestine of juvenile sea cucumbers. One group was fed the basal diet (control group), while three other groups were fed the basal diet supplemented with B. cereus G19 (G19 group), B. cereus BC-01 (BC group), or P. marcusii DB11 (PM group). The growth rate of sea cucumbers fed diets with probiotics supplementation was significantly higher than that of the control group (P < 0.05). Sea cucumbers in the G19 and PM groups had a significantly greater phagocytic activity of coelomocytes compared to the control group (P < 0.05), while those in the G19 and BC groups had a greater respiratory burst activity (P < 0.05). The alkaline phosphatase (AKP) activity of coelomocytes in sea cucumbers fed diets with probiotics supplementation was significantly higher than the control group (P < 0.05). Comparatively, superoxide dismutase (SOD) activity of coelomocytes for sea cucumber in the PM group was significantly greater (P < 0.05). As for the immune-related genes, B. cereus G19 supplementation significantly increased the expression level of the Aj-rel gene in coelomocytes (P < 0.05), while B. cereus BC-01 supplementation significantly increased that of the Aj-p50 gene as compared to the control group (P < 0.05). In the intestine, the relative expression level of Aj-p105, Aj-p50, and Aj-lys genes in the PM group was significantly higher than that in the control group (P < 0.05). These results suggested that B. cereus G19 and B. cereus BC-01 supplementation could improve the growth performance and the immune response in coelomocytes, while P. marcusii DB11 supplementation could have a positive effect on the growth performance and immune response in coelomocytes and the intestine of sea cucumbers.

Histological, ultrastructural and heat shock protein 70 (HSP70) responses to heat stress in the sea cucumber Apostichopus japonicus

The aquaculture industry for Apostichopus japonicus has suffered severe economic and resource losses due to high temperature in recent summers. There is increasing concern about the effect of high temperature on this species. Histological, ultrastructural and HSP70 responses to heat stress were investigated in the intestine of A. japonicus. Tissue degradation was observed in muscular, submucosal and mucosal layers, with significant decrease in plicae circulares of the mucosal layer. Ultrastructural damage intensified with increasing stress time, and indicators of cell apoptosis were evident after 192 h heat stress. Immunostaining showed HSP70 mainly in mucosa and serosa, with faint staining in non-stressed individuals (the control group) and denser staining under stress (the 6, 48 and 192 h groups). Western blot detection confirmed ocurrence of HSP70 in all groups and significant up-regulation under stress. The rapid and persistent response of HSP70 implies its critical role in the heat shock response of A. japonicus.

Impact of CO2-driven acidification on the development of the sea cucumber Apostichopus japonicus (Selenka) (Echinodermata: Holothuroidea)

We evaluated the impact of ocean acidification on the early development of sea cucumber Apostichopus japonicus. The effect of pH-levels (pH 8.04, 7.85, 7.70 and 7.42) were tested on post-fertilization success, developmental (stage duration) and growth rates. Post-fertilization success decreased linearly with pH leading to a 6% decrease at pH 7.42 as compared to pH 8.1. The impact of pH on developmental time was stage-dependent: (1) stage duration increased linearly with decreasing pH in early-auricularia stage; (2) decreased linearly with decreasing pH in the mid-auricularia stage; but (3) pH decline had no effect on the late-auricularia stage. At the end of the experiment, the size of doliolaria larvae linearly increased with decreasing pH. In conclusion, a 0.62 unit decrease in pH had relatively small effects on A. japonicus early life-history compared to other echinoderms, leading to a maximum of 6% decrease in post-fertilization success and subtle effects on growth and development.

Feeding behavior and digestive physiology in sea cucumber Apostichopus japonicus

The feeding behavior and digestive physiology of the sea cucumber, Apostichopus japonicus are not well understood. A better understanding may provide useful information for the development of the aquaculture of this species. In this article the tentacle locomotion, feeding rhythms, ingestion rate (IR), feces production rate (FPR) and digestive enzyme activities were studied in three size groups (small, medium and large) of sea cucumber under a 12h light/12h dark cycle. Frame-by-frame video analysis revealed that all size groups had similar feeding strategies using a grasping motion to pick up sediment particles. The tentacle insertion rates of the large size group were significantly faster than those of the small and medium-sized groups (P<0.05). Feeding activities investigated by charge coupled device cameras with infrared systems indicated that all size groups of sea cucumber were nocturnal and their feeding peaks occurred at 02:00-04:00. The medium and large-sized groups also had a second feeding peak during the day. Both IR and FPR in all groups were significantly higher at night than those during the daytime (P<0.05). Additionally, the peak activities of digestive enzymes were 2-4h earlier than the peak of feeding. Taken together, these results demonstrated that the light/dark cycle was a powerful environment factor that influenced biological rhythms of A. japonicus, which had the ability to optimize the digestive processes for a forthcoming ingestion.

RNA-Seq reveals dynamic changes of gene expression in key stages of intestine regeneration in the sea cucumber Apostichopus japonicus. [corrected]

BACKGROUND

Sea cucumbers (Holothuroidea; Echinodermata) have the capacity to regenerate lost tissues and organs. Although the histological and cytological aspects of intestine regeneration have been extensively studied, little is known of the genetic mechanisms involved. There has, however, been a renewed effort to develop a database of Expressed Sequence Tags (ESTs) in Apostichopus japonicus, an economically-important species that occurs in China. This is important for studies on genetic breeding, molecular markers and special physiological phenomena. We have also constructed a library of ESTs obtained from the regenerative body wall and intestine of A. japonicus. The database has increased to ~30000 ESTs.

RESULTS

We used RNA-Seq to determine gene expression profiles associated with intestinal regeneration in A. japonicus at 3, 7, 14 and 21 days post evisceration (dpe). This was compared to profiles obtained from a normally-functioning intestine. Approximately 5 million (M) reads were sequenced in every library. Over 2400 up-regulated genes (>10%) and over 1000 down-regulated genes (~5%) were observed at 3 and 7dpe (log2Ratio ≥ 1, FDR ≤ 0.001). Specific "Go terms" revealed that the DEGs (Differentially Expressed Genes) performed an important function at every regeneration stage. Besides some expected pathways (for example, Ribosome and Spliceosome pathway term), the "Notch signaling pathway," the "ECM-receptor interaction" and the "Cytokine-cytokine receptor interaction" were significantly enriched. We also investigated the expression profiles of developmental genes, ECM-associated genes and Cytoskeletal genes. Twenty of the most important differentially expressed genes (DEGs) were verified by Real-time PCR, which resulted in a trend concordance of almost 100% between the two techniques.

CONCLUSION

Our studies demonstrated dynamic changes in global gene expression during intestine regeneration and presented a series of candidate genes and enriched pathways that contribute to intestine regeneration in sea cucumbers. This provides a foundation for future studies on the genetics/molecular mechanisms associated with intestine regeneration.

Physiological responses in a variable environment: relationships between metabolism, hsp and thermotolerance in an intertidal-subtidal species

Physiological responses to temperature reflect the evolutionary adaptations of organisms to their thermal environment and the capability of animals to tolerate thermal stress. Contrary to conventional metabolism theory, increasing environmental temperatures have been shown to reduce metabolic rate in rocky–eulittoral-fringe species inhabiting highly variable environments, possibly as a strategy for energy conservation. To study the physiological adaptations of an intertidal-subtidal species to the extreme and unpredictable heat stress of the intertidal zone, oxygen consumption rate and heat shock protein expression were quantified in the sea cucumber Apostichopus japonicus. Using simulate natural temperatures, the relationship between temperature, physiological performance (oxygen consumption and heat shock proteins) and thermotolerance were assessed. Depression of oxygen consumption rate and upregulation of heat shock protein genes (hsps) occurred in sequence when ambient temperature was increased from 24 to 30°C. Large-scale mortality of the sea cucumber occurred when temperatures rose beyond 30°C, suggesting that the upregulation of heat shock proteins and mortality are closely related to the depression of aerobic metabolism, a phenomenon that is in line with the concept of oxygen- and capacity-limited thermal tolerance (OCLTT). The physiologically-related thermotolerance of this sea cucumber should be an adaptation to its local environment.

Molecular characterization and expression analysis of a complement component 3 in the sea cucumber (Apostichopus japonicus)

The complement system has been discovered in invertebrates and vertebrates, and plays a crucial role in the innate defense against common pathogens. As a central component in the complement system, complement component 3 (C3) is an intermediary between innate and adaptive immune system. In this study, a new isoform of C3 in the sea cucumber Apostichopus japonicus, termed AjC3-2 was identified. Its open reading frame (ORF) is 5085 bp and encodes for 1695 amino acids with a putative signal peptide of 20 amino acid residues. The mature protein molecular weight of AjC3-2 was 187.72 kDa. It has a conserved thioester site and a linker R(689)RRR(692) where AjC3-2 is splitted into β and α chain during posttranslational modification. The expression patterns of two distinct sea cucumber C3 genes, AjC3-2 and AjC3, were similar. During the different development stages from unfertilized egg to juvenile of the sea cucumber, the highest expression levels of AjC3-2 and AjC3 genes were both found in late auricularia. In the adult, the highest expression of these two genes was observed in the coelomocytes and followed by the body wall. AjC3-2 and AjC3 genes expression increased significantly at 6 h after the LPS challenge. These results indicated that these two C3 genes play a pivotal role in immune responses to the bacterial infection in sea cucumber.

Difference in thermotolerance between green and red color variants of the Japanese sea cucumber, Apostichopus japonicus Selenka: Hsp70 and heat-hardening effect

We studied thermal tolerance limits, heat-hardening, and Hsp70 to elucidate the difference in thermotolerance between two color variants of the sea cucumber Apostichopus japonicus. Green and Red variants occupy different habitats and have different aestivation responses to high temperature in summer. In the absence of heat-hardening, the variants showed no difference in the temperature at which 50% of the individuals died: Green, 31.49 degrees C; Red, 31.39 degrees C. However, Green specimens acquired higher thermotolerance than Red after a prior sublethal heat exposure. After 72 h of recovery from a heat-hardening treatment (30 degrees C for 2 h), the survival of Green variants was more than 50% and that of Red was less than 5% when they were treated at 33 degrees C for 2 h. Levels of mRNA and protein for Hsp70 were significantly higher in Green than Red after the heat shock of 30 degrees C, and the stability of hsp70 mRNA of Green was significantly higher than that of Red. Our findings suggest that within the same species, different variants that have similar thermal limits in the absence of heat-hardening can acquire different thermotolerances after a prior sublethal heat shock. The difference in induced thermotolerance between Green and Red is closely related to the expression pattern of Hsp70, which was partly governed by the stability of hsp70 mRNA.

[Etiology of off-plate syndrome in cultured larval Apostichopus japonicus at attachment stage and analysis of reservoir of pathogens]

OBJECTIVE

To clarify pathogens and sources of the off-plate syndrome at the attachment stage in the larval culture of Apostichopus japonicus, and further to find out effective medicines for this disease.

METHODS

Etiological analysis was performed on larvae with typical off-plate syndrome from three larvae culture factories. Suspicious pathogens were used for artificial infection test, and were identified through morphological, physiological and biochemical tests, and 16S rDNA sequence analysis. Quantitative bacterial analysis was done on the culture systems of the three factories, including water sources, rearing water, ordure (in the pond floor), attachments and feeds. Finally, drug-sensitive tests were done against the pathogens.

RESULTS

A common dominant bacterium strain was isolated from all ill larvae included in the study. Artificial infection test showed it was the causative pathogen associated with the disease, and the artificially infected sea cucumbers had same syndromes to the naturally ill ones. The bacterium was identified as Vibrio sp. Bacterial quantity of water sources was in the qualified range (<50 cfu/mL), while out of the standard range in others (> 1 x 10(5) cfu/mL). The sources of the pathogen were complicated, since pathogens were discovered in the water sources, rearing water, ordure, attachments and feeds. However, the density of causative bacteria was the highest in the feeds, middle in the attachments, and lowest in the water sources. Twelve antibiotics could inhibit growth of the pathogens.

CONCLUSION

The possible pathogen for off-plate syndrome was Vibrio sp. Feeds may be the main source of the pathogen. Twelve antibiotics besides nalidixic acid could be applied for disease prevention and treatment of Apostichopus japonicus.

Microsatellite analysis of Japanese sea cucumber, Stichopus (Apostichopus) japonicus, supports reproductive isolation in color variants

The genetic relationship among the three color variants (Red, Green, and Black) of the Japanese sea cucumber, S. japonicus, was investigated using 11 microsatellite markers. Genetic differentiation testing among the three sympatric color types showed the strong heterogeneity of Red (p<0.001), while no significant difference was observed between Green and Black (p=0.301 to 0.961). UPGMA trees constructed from 10 sample lots from 5 localities showed two distinct clusters, one from the Red types and the other from the Green and Black types. In addition, the sympatric Green and Black formed one subcluster with strong bootstrap support at each locality. These results indicate the separate species status of Red and the other color types, and also support the population identity of sympatric Green and Black.