Molecular characterization of a cathepsin L1 highly expressed in phagocytes of pacific oyster Crassostrea gigas

CTSL-2 upon specifically recognizing Vibrio splendidus directly cleaves complement C3 to promote the bacterial phagocytosis and degradation in oyster

Cathepsin L (CTSL) as a cysteine cathepsin protease mediates complement C3 cleavage and pathogen degradation. In the present study, a CTSL homolog was identified from Crassostrea gigas (designated as CgCTSL-2). Its mRNA expression increased significantly in hemocytes after Vibrio splendidus stimulation. The activity of rCgCTSL-2 was induced after incubation with LPS or V. splendidus in Ca2+-dependent manner. rCgCTSL-2 could specifically bound V. splendidus in Ca2+-dependent manner. The co-localization of rCgCTSL-2 and V. splendidus was observed in cell-free hemolymph. Upon binding V. splendidus, CgCTSL-2 interacted with CgC3 in cell-free hemolymph and hemocytes. CgC3 fragments in CgCTSL-2-RNAi oysters and full length CgC3 in rCgCTSL-2-treated oysters were both reduced in cell-free hemolymph, respectively. CgC3 fragments were accumulated in CgCTSL-2-RNAi or rCgCTSL-2-treated oysters. The co-localizations of V. splendidus, CgC3, CgCD18, CgCTSL-2 and lysosomes were observed in hemocytes. These results suggested that CgCTSL-2 upon binding V. splendidus directly interacted with CgC3 to lead to CgC3 cleavage and then CgC3 fragments coated on V. splendidus were mediated by CgCD18 into CTSL-2-lysosome pathway.

Identification, molecular characterization and expression patterns of Cathepsin L in Yesso scallop (Patinopecten yessoensis) shell-infested by Polydora

Patinopecten yessoensis (Yesso scallop), one of the most important aquaculture molluscs in China, has recently suffered severe Polydora disease, causing economic losses. Cathepsin L (CatL), a cysteine protease, has important functions in immune responses in vertebrates and invertebrates. However, little is known regarding the structure and function of CatL in scallops. In this study, a CatL gene named PyCatL was first identified in the genome of P. yessoensis. Gene structure analysis of PyCatL revealed it had 8 exons and 7 introns and a full length of 7916 bp. The gene sequence was analysed, and typically conserved functional domains (signal peptide, inhibitor I29 domain, and peptidase C1 domain) and motifs (ERWNIN, GNYD and GCXGG) of CatL were all predicted in PyCatL, confirming the sequence as belonging to a CatL gene. Phylogenetic analysis showed the evolutionary status of CatL was consistent with the species taxonomy. PyCatL was expressed ubiquitously in all the tested tissues in this study, suggesting its involvement in a wide range of physiological processes. After Polydora infestation, PyCatL exhibited significant upregulation in various mantle regions at both mRNA and protein levels, contrasting with a notable decrease in gene expression in hemocytes. Additionally, the enzyme activity of PyCatL showed a significant increase in the mantle of diseased P. yessoensis. The results suggested a role for mantle tissue in response to Polydora infestation by upregulating expression of PyCatL. The study offers novel insights into the function of CatL in innate immunity in scallops.

A transcription factor ATF3 involves in the phagocytosis of granulocytes in oyster Crassostrea gigas

Phagocytosis is a major cellular mechanism for mollusk granulocytes to eliminate nonself substances and dead cells, and thus to preserve the immune homeostasis. The knowledge of the regulatory mechanisms controlling phagocytic capacity is vital to understanding the immune system. In the present study, an ATF3 homolog (CgATF3) with a typical bZIP domain was identified in the Pacific oyster Crassostrea gigas. Its highly conserved bZIP domain consisted of two structural features, a basic region for DNA binding and a leucine zipper region for dimerization. Its transcript was found to be abundantly expressed in haemocytes, which was induced by Vibrio splendidus stimulation and recombinant CgTNF-2 treatment, along with an increase of its protein content in the nucleus. Moreover, CgATF3 showed a consistent and specific high expression in granulocytes, and CgATF3+ granulocytes were characterized morphologically by the largest diameter, smaller nucleus to cytoplasmic ratio, and abundant cytoplasmic granules, and functionally by a higher capacity for phagocytosis. When CgATF3 expression was inhibited by RNAi, the expression levels of CgRab1, CgRab33 and CgCathepsin L1, as well as the phagocytic rate and index of granulocytes all decreased after V. splendidus stimulation. These results together demonstrated the involvement of CgATF3 in regulating the expressions of Rabs and Cathepsin L1, as well as the phagocytosis of granulocytes in oyster C. gigas.

Dietary Supplementation of Chlorella vulgaris Effectively Enhanced the Intestinal Antioxidant Capacity and Immune Status of Micropterus salmoides

An M. salmoides fish meal diet was supplemented with 0 (CHL0, Control), 38 (CHL38), 76 (CHL76), 114 (CHL114), and 152 (CHL152) mg/kg C. vulgaris for 60 days, and their serum and intestinal samples were analyzed. The results showed that the albumin (ALB) and total protein (TP) contents were observably enhanced in the CHL76 group compared with the Control group. The intestinal glutathione (GSH) and glutathione peroxidase (GSH-Px) contents were enhanced significantly in the CHL76 group, while the total antioxidant capacity (T-AOC) was enhanced in the CHL38 group, compared with the Control group. However, supplementation of >76 g/kg C. vulgaris significantly inhibited the superoxide dismutase (SOD) activity in the intestines of M. salmoides. Moreover, the malondialdehyde (MDA) content was observably dropped in the CHL-supplemented groups compared with the Control group. Transcriptome analysis of the CHL76 and Control groups displayed a total of 1384 differentially expressed genes (DEGs). KEGG analysis revealed that these DEGs were enriched in apoptosis, cytokine-cytokine receptor interaction, tight junction (TJ), and phagosome signaling pathways, which were associated with improved intestinal immunity in the CHL76 group. Additionally, the DEGs enriched in the above pathways were also correlated with the antioxidant parameters, such as catalase (CAT), GSH, GSH-Px, SOD, T-AOC, and MDA. Therefore, our study found that dietary supplementation of C. vulgaris effectively enhanced the intestinal antioxidant capacity of M. salmoides by increasing antioxidant enzyme activity and decreasing MDA content. Additionally, dietary supplementation of C. vulgaris improved the intestinal immune status of M. salmoides by reducing proapoptotic and proinflammatory factors, increasing intestinal TJs- and phagosome-related genes expressions, and increasing the serum ALB and TP contents. Lastly, quadratic regression analysis of the serum biochemical indices (ALB and TP) and intestinal antioxidant parameters (GSH-Px and GSH) revealed that the optimal supplemental level of C. vulgaris in the M. salmoides diet was 58.25-77.7 g/kg.

Insight into crustacean cathepsins: Structure-evolutionary relationships and functional roles in physiological processes

Cathepsins belong to a group of proteins that are present in both prokaryotic and eukaryotic organisms and have an extremely high degree of evolutionary conservation. These proteins are functionally active in extracellular environments as soluble enzymatic proteins or attached to plasma membrane receptors. In addition, they occur in cellular secretory vesicles, mitochondria, the cytosol, and within the nuclei of eukaryotic cells. Cathepsins are classified into various groups based on their sequence variations, leading to their structural and functional diversification. The molecular understanding of the physiology of crustaceans has shown that proteases, including cathepsins, are expressed ubiquitously. They also contain one of the central regulatory systems for crustacean reproduction, growth, and immune responses. This review focuses on various aspects of the crustaceans cathepsins and emphasizes their biological roles in different physiological processes such as reproduction, growth, development, and immune responses. We also describe the bioactivity of crustaceans cathepsins. Because of the vital biological roles that cathepsins play as cellular proteases in physiological processes, they have been proposed as potential novel targets for the development of management strategies for the aquaculture industries.

Genomic and transcriptomic identification of the cathepsin superfamily in the Mediterranean mussel Mytilus galloprovincialis

Cathepsins are lysosomal enzymes that participate in important physiological processes, such as development, tissue remodelling, senescence and innate and adaptive immunity. The description of these proteins in molluscs is fragmented and incomplete. In the present work, we identified most of the cathepsin family members in the bivalve Mytilus galloprovincialis by screening published genomic and transcriptomic information. In this specie, the cathepsin family is composed of 41 proteins showing a high diversification of cathepsins D, L and F, not previously observed in other taxonomic groups. Specific set of cathepsins are constitutively expressed in the different mussel tissues. Transcriptomic analyses suggested coordinated activity of the different cathepsins and their sequential activation during larval development. Cathepsins also play an important role in the immune response of bivalves, and different immune pathways seem to be activated in response to Vibrio splendidus infection.

Quantitative proteomic analysis reveals the molecular mechanism of the Yesso scallop (Patinopecten yessoensis) in response to Polydora infection

The Yesso scallop is a large and ancient molluscan group with great economic value; however, it has recently suffered severe cases of Polydora infection. Polydora parasitizes the shells of scallops, badly damaging shell structures and affecting growth and mortality. To investigate the molecular mechanism of Yesso scallops’ response to Polydora infection, proteomic profiling changes in the mantle tissues of Polydora-infected (diseased) and healthy scallops were systematically analysed by tandem mass tags (TMT) labelling technology in this study. A total of 519 differentially expressed proteins (DEPs) were identified. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed most innated immune-related functions and pathways were significantly downregulated in diseased scallops, except the phagocytosis pathway, indicating an important role of phagocytosis in response to Polydora infection. DEPs involved in the phagocytosis pathway were associated with phagocytic receptor recognition, phagosome biogenesis and pathogen degradation, and they were further verified by quantitative real-time PCR. The results elucidate the molecular components of phagocytosis in molluscs for the first time. Polydora can be encapsulated by melanization with an obvious appearance in shells; indeed, melanization-related DEPs were upregulated in diseased scallops. Inhibition of apoptosis and nervous modulation may be also involved in the response mechanism, with some highly associated proteins significantly differentially expressed. Finally, a protein–protein interaction network was constructed to provide a global view of the interaction relationships of the DEPs. The study predicts the molecular response mechanism of Yesso scallops to Polydora infection, and lays a theoretical foundation for Polydora disease control.

CgRab1 regulates Cgcathepsin L1 expression and participates in the phagocytosis of haemocytes in oyster Crassostrea gigas

Rab protein plays an important role in a variety of cellular activities, especially the fusion process of the inner membrane during endocytosis. In the present study, a Rab1 protein (CgRab1) was identified from the Pacific oyster Crassostrea gigas. The full-length cDNA sequence of CgRab1 was of 2248 bp with an open reading frame of 618 bp, encoding a polypeptide of 205 amino acids containing a Rab domain. The deduced amino acid sequence of CgRab1 shared 94.2% and 89.3% identity with Rab1 from Pomacea canaliculata and Homo sapiens respectively. In the phylogenetic tree, CgRab1 was firstly clustered with the Rab1s from Aplysia californica and Pomacea canaliculata to form a sister group with Rab1 from invertebrates. The recombinant CgRab1 protein (rCgRab1) was able to bind GTP. The mRNA transcripts of CgRab1 were highly expressed in oyster haemocytes, and its expression level in oyster haemocytes was significantly up-regulated at 24 h after the stimulations with Vibro splendidus, which was 2.43-fold (p < 0.01) of that in the control group. After the expression of CgRab1 was knocked down (0.38-fold of that in EGFP-RNAi experimental group) by RNAi，the protein expression of Cgcathepsin L1 were reduced (0.63-fold, p < 0.01) compared with that in EGFP-RNAi experimental group. The phagocytic rate and phagocytic index of haemocytes in CgRab1-RNAi oysters decreased after V. splendidus stimulation, which was 0.50-fold (p < 0.01) and 0.58-fold (p < 0.01) of that in EGFP-RNAi experimental group. These results indicated that CgRab1 was involved in the process of haemocytes phagocytosis by regulating the expression of Cgcathepsin L1 in oyster C. gigas.

Effect of Different Species of Prorocentrum Genus on the Japanese Oyster Crassostrea gigas Proteomic Profile

This paper assesses the effects of exposure to toxic concentrations (1200 to 6000 cells/mL) of the dinoflagellates Prorocentrum lima, Prorocentrum minimum, and Prorocentrum rhathymum and several concentrations of aqueous and organic extracts obtained from the same species (0 to 20 parts per thousand) on the Crassostrea gigas (5-7 mm) proteomic profile. Through comparative proteomic map analyses, several protein spots were detected with different expression levels, of which eight were selected to be identified by liquid chromatography-mass spectrometry (LC-MS/MS) analyses. The proteomic response suggests that, after 72 h of exposure to whole cells, the biological functions of C. gigas affected proteins in the immune system, stress response, contractile systems and cytoskeletal activities. The exposure to organic and aqueous extracts mainly showed effects on protein expressions in muscle contraction and cytoskeleton morphology. These results enrich the knowledge on early bivalve developmental stages. Therefore, they may be considered a solid base for new bioassays and/or generation of specific analytical tools that allow for some of the main effects of algal proliferation phenomena on bivalve mollusk development to be monitored, characterized and elucidated.