CgATP synthase β subunit involved in the regulation of haemocytes proliferation as a CgAstakine receptor in Crassostrea gigas

A bone morphogenetic protein regulates the shell formation of Crassostrea gigas under ocean acidification

Bone morphogenetic proteins (BMPs) are key factors controlling osteoblast differentiation, which have been proved to be involved in the hard tissue formation of marine mollusks. In the present study, a member of BMPs gene (CgBMP7) was identified from Pacific oyster Crassostrea gigas (C. gigas) with the aim to understand its possible role in the regulation of shell formation under ocean acidification (OA) conditions. The open reading frame (ORF) of CgBMP7 was of 1254 bp encoding a polypeptide of 417 amino acids. The deduced amino acid sequence of CgBMP7 was comprised of one signal peptide, one prodomain and one TGF-β domain, which shared 21.69%-61.10% identities with those from other species. The mRNA transcript of CgBMP7 was ubiquitously expressed in all the tested tissues of adult oysters with a higher expression level in mantle, notably highest in the middle fold (MF) of the three folds of mantle. The expression level of bone morphogenetic protein type I receptor (CgBMPR1B) mRNA was also highest in the MF and up-regulated dramatically post recombinant BMP7 protein (rCgBMP7) stimulation. After the blockage of BMPR1B with inhibitor LDN193189 (LDN), the mRNA expression level and phosphorylation level of CgSmad1/5/8 in mantle were decreased, and the mRNA expression levels of CgCaM and Cgengrailed-1 were down-regulated significantly. During the oysters were exposed to acidified seawater for weeks, the expression levels of CgBMP7, CgBMPR1B and CgSmad1/5/8 in the MF decreased significantly (p < 0.01) at the 4th week, and CgCaM and Cgengrailed-1 also exhibited the same variable expression patterns as CgBMP7. In addition, the growth of shell in the treatment group (pH 7.8) was slower than that in the control group (pH 8.1). These results collectively indicated that BMP7 was able to trigger the BMPR-Smad signaling pathway and involved in controlling the formation of oyster calcified shell under OA conditions.

A pattern recognition receptor CgTLR3 involves in regulating the proliferation of haemocytes in oyster Crassostrea gigas

Toll-like receptors (TLRs) are expressed on various immune cells as key elements of innate and adaptive immunity, and they also play significant roles in regulating cell proliferation and differentiation. In the present study, the binding activity of CgTLR3 to PAMPs and CgMyD88-2, and its role in mediating the proliferation of haemocytes was investigated. The recombinant proteins of the extracellular six LRR domains (rCgTLR3-LRR) and intracellular TIR domain (rCgTLR3-TIR) of CgTLR3 were obtained respectively. rCgTLR3-LRR exhibited binding activity to lipopolysaccharide (LPS), peptidoglycan (PGN), mannan (MAN) and Poly (I:C), with the highest affinity for LPS. While rCgTLR3-TIR displayed binding activity to the recombinant protein of rCgMyD88-2, with KD value of 7.22 × 10-7 M. The CgTLR3 mRNA and protein were detected in three subpopulations of oyster haemocytes, and they were mainly concentrated in granulocytes, which was 7.27-fold (p < 0.05) of that in semi-granulocytes and 8.51-fold (p < 0.01) of that in agranulocytes. The percentage of CgTLR3 positive cells (FITC+ haemocytes) in granulocytes was 4.45-fold (p < 0.01) and 2.57-fold (p < 0.05) of that in agranulocytes and semi-granulocytes, respectively. After Vibrio splendidus stimulation, the mRNA expression level of CgTLR3 in haemocytes significantly upregulated at 6 h and 12 h, which was 2.93-fold (p < 0.05) and 4.15-fold (p < 0.05) of that in the control group. After the expression of CgTLR3 was inhibited by the injection of si-CgTLR3, the expression levels of transcription factors associated with hematopoiesis (CgGATA, CgRunx), cell cycle-related genes (CgPCNA, CgCDC-45, CgCDK-2), the agranulocyte marker CgCD-9, the granulocyte marker CgAATase, and the inflammatory factor CgIL17-1 significantly decreased (p < 0.05) after the V. splendidus stimulation, which were 0.43-fold, 0.83-fold, 0.48-fold, 0.44-fold, 0.53-fold, 0.7-fold, 0.62-fold, and 0.47-fold of that in NC + V. s group in vivo, respectively. Meanwhile, the percentage of EdU+ haemocytes in si-CgTLR3+V. s group was significantly reduced by 0.54-fold (p < 0.05) compared to the control group (2.7%). These results collectively indicated that CgTLR3 was involved in modulating the proliferation of haemocytes by regulating the expression of proliferation-related genes and inflammatory factor in oyster C. gigas.

Soluble mediators of innate immunity in annelids and bivalve mollusks: A mini-review

Annelids and mollusks, both in the superphylum of Lophotrochozoa (Bilateria), are important ecological groups, widespread in soil, freshwater, estuarine, and marine ecosystems. Like all invertebrates, they lack adaptive immunity; however, they are endowed with an effective and complex innate immune system (humoral and cellular defenses) similar to vertebrates. The lack of acquired immunity and the capacity to form antibodies does not mean a lack of specificity: invertebrates have evolved genetic mechanisms capable of producing thousands of different proteins from a small number of genes, providing high variability and diversity of immune effector molecules just like their vertebrate counterparts. This diversity allows annelids and mollusks to recognize and eliminate a wide range of pathogens and respond to environmental stressors. Effector molecules can kill invading microbes, reduce their pathogenicity, or regulate the immune response at cellular and systemic levels. Annelids and mollusks are "typical" lophotrochozoan protostome since both groups include aquatic species with trochophore larvae, which unite both taxa in a common ancestry. Moreover, despite their extensive utilization in immunological research, no model systems are available as there are with other invertebrate groups, such as Caenorhabditis elegans or Drosophila melanogaster, and thus, their immune potential is largely unexplored. In this work, we focus on two classes of key soluble mediators of immunity, i.e., antimicrobial peptides (AMPs) and cytokines, in annelids and bivalves, which are the most studied mollusks. The mediators have been of interest from their first identification to recent advances in molecular studies that clarified their role in the immune response.

ROS function as an inducer of autophagy to promote granulocyte proliferation in Pacific oyster Crassostrea gigas

Hematopoiesis is the biological process to generate new blood cells in the living body and reactive oxygen species (ROS) contribute significantly to the regulation of haematopoietic cell homeostasis. In the present study, the involvement of ROS in the proliferation of haemocytes was examined in Pacific oyster Crassostrea gigas. The ROS content in haemocytes increased significantly after lipopolysaccharide (LPS) treatment, but decreased after the treatment with antioxidant N-Acetyl-L-cysteine (NAC, a scavenger of ROS). The percentage of 5-ethynyl-2'-deoxyuridine labeled (EdU⁺) granulocytes in total haemocytes significantly increased at 12 h (4.12-fold, p < 0.001) and 24 h (2.36-fold, p < 0.001) after LPS treatment, while decreased at 12 h (0.26-fold, p < 0.001) and 24 h (0.61-fold, p < 0.05) after NAC treatment, respectively. Meanwhile, the percentage of haemocytes with autophagosome positive signals significantly increased at 12 h (1.17-fold, p < 0.01) and 24 h (1.19-fold, p < 0.05) after LPS treatment, but significantly reduced at 12 h (0.41-fold, p < 0.001) and 24 h (0.28-fold, p < 0.001) after the NAC treatment, respectively. After ammonium chloride (NH₄Cl) treatment, the percentage of haemocytes with autophagosome and EdU⁺ granulocytes significantly increased at 12 h, which was 1.27-fold (p < 0.01) and 1.70-fold (p < 0.01) of control group, respectively. These results collectively suggested that ROS produced after LPS treatment could act as an inducer for autophagy and involved in regulating the proliferation of some granulocytes in C. gigas.