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Molecular adaptation of caspase genes to salinity stress in the tropical sea cucumber Stichopus monotuberculatus: A comparative analysis across echinoderms.

Apoptosis is an essential physiological process that plays a critical role in development and tissue homeostasis. Caspases, as central regulators of apoptosis, are crucial in controlling inflammation and cell death. In this study, we investigated the caspase gene family in Stichopus monotuberculatus to explore their potential roles in salinity stress adaptation. Five caspase genes were identified from the genome of S. monotuberculatus, including Smcaspase3, Smcaspase6, Smcaspase8a, Smcaspase8b, and Smcaspase8c. Phylogenetic analysis revealed that these Smcaspase genes clustered into distinct caspase subfamilies and showed high conservation with homologs from other echinoderms and representative vertebrates. Conserved motif and gene structure analyses showed relatively similar structural patterns within each clade, whereas divergence was observed among different subfamilies. Promoter analysis identified numerous cis-acting elements related to gene regulation, immune response, and growth and development. Expression profiling under salinity stress showed that Smcaspase8a was significantly upregulated, particularly under prolonged stress, whereas the other genes exhibited limited transcriptional responses. Our findings highlight caspase function in salinity stress and provide the foundation of molecular salinity adaptation mechanisms in S. monotuberculatus.

Animals

Genome-wide identification of the HSP70 superfamily in tropical sea cucumber Stichopus monotuberculatus and their expression analysis under low-salinity stress.

Heat shock proteins (HSPs) are a group of evolutionarily conserved molecular chaperones that serve as indispensable core regulators in preserving cellular homeostasis and orchestrating organismal stress responses. The tropical sea cucumber Stichopus monotuberculatus, a high-value aquaculture species, is sensitive to fluctuations in environmental salinity-a challenge that has emerged as a critical bottleneck limiting its large-scale commercial cultivation. However, no systematic investigation has been conducted to characterize the HSP70 superfamily in S. monotuberculatus and elucidate its functional roles in salinity adaptation. In the present study, we performed a comprehensive genome-wide scan and identified 19 HSP70 superfamily genes in the S. monotuberculatus genome, with the HSP70IV subfamily showing remarkable gene expansion, containing 8 distinct copies. Phylogenetic analysis, conserved motif identification, and gene structure characterization demonstrated high evolutionary conservation within each HSP subfamily. These genes were unevenly distributed across the chromosomes of S. monotuberculatus, and prediction of cis-acting elements revealed that their upstream regulatory regions were enriched with numerous functional elements associated with stress response and immune regulation. Salinity stress experiments revealed that under severe low-salinity conditions (18‰), the expression levels of SmHSPA14L and multiple HSP70IV subfamily members were significantly elevated, while SmHYOU1D was significantly downregulated; in contrast, only subtle changes were detected in the expression of most HSP70 genes under moderate low-salinity stress (24‰). These findings strongly suggest that HSP70 genes, particularly the expanded HSP70IV subfamily, may act as key modulators in the low-salinity stress response. This work provides valuable insight into the molecular mechanisms underlying salinity adaptation in tropical sea cucumbers.

Animals

Transcriptomic characterization of the intestine in Stichopus monotuberculatus under gradient temperature stress and HSP gene family-mediated molecular adaptation.

The increasing frequency of extreme temperature events under climate change poses a growing threat to the stability of tropical sea cucumber aquaculture. To characterize the molecular responses of the tropical sea cucumber Stichopus monotuberculatus to acute temperature stress, juveniles were exposed for 96 h to 15 °C, 20 °C, 25 °C, 30 °C, and 35 °C, followed by transcriptomic profiling of the intestine. By transcriptomic analysis, 2258, 634, 1618, and 2980 differentially expressed genes (DEGs) were identified at 15, 20, 30, and 35 °C compared to control, respectively. More DEGs were generally detected at temperatures further from 25 °C, with the 35 °C group showing the largest transcriptional response. Although cold and heat stress both affected metabolism and protein homeostasis, their enrichment profiles differed. At 15 °C, DEGs were mainly enriched in the spliceosome and p53 signaling pathways, highlighting RNA processing and p53 signaling as prominent features of the cold-stress response. At 35 °C, DEGs were mainly enriched in the PI3K-Akt signaling pathway, ubiquitin-mediated proteolysis, and mitophagy, indicating enhanced regulation of cell survival, protein turnover, and mitochondrial quality control. HSP genes also responded differently to cold and heat stress. Most HSP70 and HSP90 family members were downregulated at low temperatures, whereas HSP70 genes and small heat shock proteins were markedly upregulated at high temperatures. Overall, the intestinal transcriptome showed distinct responses to cold and heat stress. These results identify pathways and HSP genes potentially involved in the temperature response of S. monotuberculatus and provide useful information for evaluating temperature tolerance and defining suitable temperatures for its aquaculture.

Heat shock protein

Glycosaminoglycan involved in the cation-induced change of body wall structure of sea cucumber Stichopus japonicus.

The body wall of sea cucumber Stichopus japonicus was treated with various concentrations of several cations, and examined for changes in toughness, taking punch force as parameter. Toughness of the body wall tended to decrease with increasing concentration of each cation, but in different modes depending mainly upon the valency of cation: e.g., the body wall completely lost toughness in 0.3 M Na+ or 0.4 M K+, whereas it retained more than half the initial toughness even in 0.4 M Ca2+ or Mg2+. Glycosaminoglycan (GAG) from the body wall was dissolved in water, and examined for viscosity changes as caused by those cations. Specific viscosity (eta sp) decreased from 0.71 (without cation) to 0.47-0.57 in the presence of 0.1 M monovalent and divalent cations. At 0.4 M, monovalent cations reduced eta sp to 0.38-0.46, but divalent cations increased eta sp to 0.56-0.63. Electron microscopy demonstrated that GAG matrix was clearly observed in the absence of cation, but disappeared in 0.4 M NaCl, forming wide free spaces in the body wall. These results all suggested that GAG is closely involved in the change of toughness of sea cucumber body wall.

Animals

Antithrombotic and anticoagulant activity of depolymerized fragment of the glycosaminoglycan extracted from Stichopus japonicus Selenka.

The antithrombotic and anticoagulant activities of depolymerized fragment (DHG-1) of glycosaminoglycan extracted from Stichopus japonicus Selenka (FGAG) were compared with those of unfractionated heparin (UFH) or low molecular weight heparin (LMWH). DHG-1 at more than 0.3 mg/kg i.v. significantly prevented death of mice treated with thrombin (800 U/kg i.v.). Under the same conditions, FGAG, UFH and LMWH significantly prevented death of mice at more than 0.3, 0.3 and 0.6 mg/kg i.v., respectively. In normal plasma, the concentration required to double the activated partial thromboplastin time (doubling APTT) of DHG-1, FGAG, LMWH and UFH were 12.0, 2.4, 5.8, and 1.2 micrograms/ml, respectively. In antithrombin III (AT III)-depleted plasma, doubling APTT of DHG-1, FGAG, and UFH were 11.3, 2.1, and 18.5 micrograms/ml, respectively. Prothrombin activation in contact-activated plasma was inhibited completely for 60 s at doubling APTT by all glycosaminoglycans used in this study. DHG-1, however, showed much less antithrombin activity than UFH as tested by thrombin clotting time in plasma and chromogenic assay in the presence of AT III. Moreover, DHG-1 showed much less inhibitory activity on factor Xa, factor IXa, and glass surface-induced factor IXa generation than UFH. These results suggested that DHG-1 is one of the promising antithrombotic agents with quite different anticoagulant property from UFH or LMWH.

Animals

Occurrence of chondroitin sulfate E in glycosaminoglycan isolated from the body wall of sea cucumber Stichopus japonicus.

Glycosaminoglycan was isolated from the body wall of sea cucumber Stichopus japonicus by a method consisting of enzymatic digestion, gel filtration, and ion-exchange chromatography. One gram of sea cucumber glycosaminoglycan was composed of 2.50 mmol of sulfate, 0.47 mmol of N-acetylgalactosamine (GalNAc), 0.53 mmol of glucuronic acid (GlcA), 1.73 mmol of fucose, and a small amount of peptide. When mildly hydrolyzed with 0.1 N H2SO4, this glycosaminoglycan released two products, one consisting of fucose plus sulfate and the other of fucose only. Partially hydrolyzed glycosaminoglycan thus obtained was composed of sulfate, GalNAc, GlcA, and fucose at a molar ratio of 3:2:2:1. Partially hydrolyzed glycosaminoglycan was easily digested with chondroitinase AC II. In ion-exchange chromatography, the digest exhibited four sharp peaks whose retention times agreed with those of unsaturated 0-(delta Di-0S), mono-(delta Di-4S and delta Di-6S), and di-(delta Di-SE) sulfated disaccharide, respectively. The disaccharide unit of sea cucumber glycosaminoglycan was composed of 22.4% chondroitin sulfate E, 11.2% chondroitin, 10.4% chondroitin 4-sulfate, and 56.0% chondroitin 6-sulfate.

Animals

[Binding of acid mucopolysaccharides of Stichopus japanicus to washed human platelets].

The binding of acid mucopolysaccharides of Stichopus japonicus Selenka (Sjamp) to washed human platelets was studied using [3H]Sjamp. The binding was rapid, reversible and with a saturable tendency. The binding reached to equilibrium at about 10 min, and 50% of [3H]Sjamp bound to the platelets at equilibrium within the first minute. When excess unlabeled Sjamp was added to the [3H]Sjamp binding suspension, [3H]Sjamp dissociated from the platelets rapidly and rather completely. Scatchard analysis revealed a class of binding sites with Kd = 2.3 +/- 0.7 micrograms/ml and Bmax = 4.5 +/- 1.2 micrograms/10(9) platelets. Separate experiments showed that the monoclonal antibody (McAb) SZ-21, a McAb to platelet membrane glycoprotein (GP) IIIa, weakened the binding, while McAb SZ-2 and SZ-22 (to GP Ib and GP IIb respectively) were ineffective. We also observed that heparin inhibited [3H]Sjamp binding to the platelets. These results indicated that the binding sites on platelets might be the Sjamp receptors. We conclude that receptor-Sjamp binding is an important process in platelet aggregation induced by Sjamp.

Animals

Mechanism of rabbit platelet agglutination induced by acidic mucopolysaccharide extracted from Stichopus japonicus Selenka.

The effects of acidic mucopolysaccharide extracted from sea cucumber (Stichopus japonicus Selenka) (SJAMP) on rabbit platelets were studied. Using citrated platelet-rich plasma (PRP), washed platelets, and formaldehyde fixed platelets from 10 New Zealand white rabbits, we investigated the effects of platelet inhibitors and various plasma and its fractions on SJAMP-induced agglutination. It was found that the tracing of platelet agglutination induced by SJAMP showed a single phase without a lag period. The lowest concentration of SJAMP required for the agglutination of rabbit platelets was approximately 2 micrograms/ml, and the magnitude of agglutination induced by SJAMP was concentration dependent. In 8 out of 10 rabbits, the platelets in PRP were agglutinated by 10 micrograms/ml of SJAMP. Platelet inhibitors, such as aspirin, indomethacin, apyrase, antimycin, 2-deoxy-D-glucose and EDTA did not inhibit the agglutination induced by SJAMP. Washed rabbit platelets were not agglutinated by SJAMP even though the concentration of SJAMP was raised up to 50 micrograms/ml. When rabbit plasma, serum, or 50-60% ammonium sulfate saturated plasma fraction was added to the reaction mixture, agglutination of washed platelets by SJAMP was recovered completely. But human plasma or fibrinogen did not have any effect on the reactivity of washed rabbit platelets to SJAMP. From these data we conclude that the SJAMP-induced rabbit platelet agglutination is independent of energy metabolism but requires plasma cofactor(s) other than fibrinogen. The plasma cofactor is present in 50-60% ammonium sulfate saturated plasma fraction.

Animals

Aggregation of human platelets by acidic mucopolysaccharide extracted from Stichopus japonicus Selenka.

The acidic mucopolysaccharide extracted from sea cucumber (Stichopus japonicus Selenka) (SJAMP) has been shown to cause platelets to aggregate. Using citrated platelet-rich plasma (PRP), washed platelets and formaldehyde-fixed platelets from humans, we investigated the effects of platelet inhibitors and various plasmas and their fractions on SJAMP-induced platelet aggregation. It was found that the lowest concentration of SJAMP required for the aggregation of human platelets was about 0.4 micrograms/ml and the magnitude of aggregation induced by SJAMP was concentration dependent. The platelets were aggregated by SJAMP at 10 micrograms/ml in 25 out of 28 (89%) normal subjects tested. Platelet inhibitors such as PGE1, aspirin, indomethacin, apyrase, antimycin, 2-deoxy-D-glucose and EDTA inhibited by 70 to 100% the aggregation induced by SJAMP. Washed platelets alone were not aggregated by SJAMP. In the presence of fibrinogen, washed platelets were aggregated by SJAMP but formaldehyde-fixed platelets were not. These data indicate that the SJAMP-induced human platelet aggregation requires extracellular calcium, fibrinogen, and energy metabolism. The second phase of aggregation is dependent upon the release of ADP, and cyclooxygenase pathway.

Animals

Collagen glycopeptides from the sea cucumber Stichopus japonicus.

Structures of several hydroxylysine-containing glycopeptides derived from the body wall of the sea cucumber have been determined. The glycosylated hydroxylysines were all the Y positions of Gly-X-Y triplets. They are thought to be distributed throughout the peptide chain, in contrast to vertebrate skin collagens. One glycopeptide demonstrated the existence of the sequence Gly-Gly-Hyp in invertebrates for the first time.

Amino Acid Sequence

[Hypocholesteremic action of trepang (Stichopus japonicus) lipids].

The hypocholesteremic effect displated by the Japan Sea trepang is shown. The experiments were carried out on rabbits with hypocholesteremia caused by fasting. Total cholesterol, beta-lipoproteids, lipoid phosphorus, total phospholipids and the cholesterol/phospholipids ratio were determined in the blood of hypercholesteremic animals. The introduction of total trepang lipids to the hypercholesteremic fasting rabbits resulted in normalization of the lipids metabolism, this being indicative of the favourable effect produced by such lipids.

Animals

Fibrinolysis relating substances in marine creatures.

1. Extracts with physiological saline solution were obtained from about 20 species of invertebrates and seaweed. Tosyl-L-Arg-MeOH hydrolysing and fibrin plate lytic activity were detected in the invertebrates Stichopus japonicus, Crassost gigas, Tapes japonica, and Kintai-gai as well as the seaweed Codiales codium. 2. These activities were all labile against heat (at 65 degrees C for 1 hr). Except for the extract from Stichopus japonicus, lytic activities against fibrin plates with and without plasminogen were similar. 3. The extract from S. japonicus showed plasminogen activating potency as well as the existence of urokinase (UK) activity enhancing factor. 4. On the other hand, the extract of the seaweed Hizikia fusiformis showed a strong UK inhibiting activity. 5. A fraction of fibrinolytic enzyme was obtained from the extract of S. japonicus by absorption to the celite affinity chromatography. It was orally administered to rabbits at a dosage of 40 mg/kg/day. 6. Fibrinolytic activity was determined periodically on the eugloblin fraction of plasma samples collected from these animals. 7. As compared with the pretreatment value, the activity increased about 2 times (P less than 0.01) and 3 times (P less than 0.005) after 4 and 8 weeks, respectively, of the treatment. 8. After 8 weeks of treatment, the kidney of treated rabbits was extracted with 2 M KCl. The activity of tissue plasminogen activator (free-type TPA) was revealed to be enhanced significantly (P less than 0.001) in the extracts. 9. The fibrinolytic enzyme increased in the blood was recognized by zymography to be mainly the UK type plasminogen activator with mol. wt of 53,000.

Animals

Distribution of alkyl and alkenyl ether-linked phospholipids and platelet-activating factor-like lipid in various species of invertebrates.

The levels of alkenylacyl, alkylacyl and diacyl subclasses of choline glycerophospholipid (CGP) and ethanolamine glycerophospholipid (EGP) fractions in 28 species of various invertebrates were studied. We found that only small amounts of either 1-alkyl-2-acyl-sn-glycero-3-phosphocholine (alkylacyl-GPC) or 1-alkenyl-2-acyl-sn-glycero-3-phosphoethanolamine (alkenylacyl-GPE) are present in most species of insects. On the other hand, almost all species examined in various phyla other than Arthropoda were shown to contain large amounts of both alkylacyl-GPC and alkenylacyl-GPE. The highest proportion of alkylacyl subclass in CGP was noted in sponge, Halichondria japonica (81.8% of CGP) and the highest proportion of alkenylacyl subclass in EGP was found in clam worm, Marphysa sanguinea (88.7% of EGP). We next surveyed the presence of platelet-activating factor (PAF)-like lipid in 45 species of invertebrates. PAF-like lipid was widely distributed among various lower animals. The highest value was obtained for sea cucumber, Stichopus japonicus, in which PAF-like lipid was present throughout the body. We also confirmed the presence of acetyltransferase activity in several lower animals. These results suggest that alkyl and alkenyl ether-linked phospholipids including PAF are physiologically important molecules particularly for invertebrates belonging to lower phyla.

Animals

Cells in the intestinal system of holothurians (Echinodermata) express cholecystokinin-like immunoreactivity.

The presence of cholecystokinin (CCK), originally isolated from porcine small intestine, has been reported in a diversity of invertebrates ranging, from cnidarians to protochordates, but so far, not in echinoderms. We have used immunohistochemical techniques to demonstrate the presence of cells expressing CCK-like immunoreactivity in the intestine of three species of sea cucumber: Holothuria mexicana, H. glaberrima, and Stichopus badionotus. The immunoreactivity was observed within the cytoplasm of these cells, in what appeared to be granular or vesicle-like structures. The cell bodies were present in the outer connective tissue layer of the intestine and had a neuronal appearance, sending an axon-like structure into the circular muscle and internal connective tissue. A plexus of fibers expressing CCK-like immunoreactivity was found overlying the muscle layer. Contractility of H. mexicana intestinal strips was studied under partially isometric conditions. CCK and related peptides induced relaxation of the basal muscle tension, and of tension induced by ACh application, suggesting a role for this agent in the intestinal physiology of holothurians.

Acetylcholine