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A C1qDC (CgC1qDC-6) with a collagen-like domain mediates hemocyte phagocytosis and migration in oysters

Huan Li, Ning Kong, Jiejie Sun, Weilin Wang, Meijia Li, Changhao Gong, Miren Dong, Min Wang, Lingling Wang, Linsheng Song
Developmental and comparative immunology 2019 v.98 pp. 157-165
Crassostrea gigas, Escherichia coli, Gram-negative bacteria, Gram-positive bacteria, Komagataella pastoris, Micrococcus luteus, Staphylococcus aureus, Vibrio splendidus, amino acids, chemotaxis, collagen, dose response, fungi, hemocytes, hepatopancreas, immune response, mannose, messenger RNA, muscles, oligomerization, oysters, pathogen-associated molecular patterns, pathogens, peptides, phagocytosis, phylogeny, polyinosinic-polycytidylic acid, protein content, signal peptide, tissues, vertebrates
Most of the bivalve C1q domain containing proteins (C1qDCs) are either only composed of the globular head domain, or contain an N-terminal coiled-coil domain, presumed to cover a role in oligomerization. On the other hand, collagen regions, widespread in vertebrate C1qDCs, are very uncommon in bivalves. In the present study, a C1qDC with a collagen-like domain (designated CgC1qDC-6) was identified from the Pacific oyster Crassostrea gigas and its possible involvement in immune responses was also characterized. The coding sequence of CgC1qDC-6 was of 756 bp, encoding a peptide of 251 amino acids with an N-terminal signal peptide, a central collagen-like domain, and a C-terminal ghC1q domain. CgC1qDC-6 was clustered with the C1qDCs from several mollusks in the phylogenetic tree. CgC1qDC-6 was detected at both mRNA and protein levels in all tested tissues including hepatopancreas, gonad, gill, mantle, adductor muscle, and hemocytes. The recombinant CgC1qDC-6 protein (rCgC1qDC-6) exhibited binding activity to various pathogen-associated molecular patterns (PAMPs) including LPS, PGN, mannose and Poly I:C, and microorganisms including Gram-negative bacteria (Escherichia coli and Vibrio splendidus), Gram-positive bacteria (Micrococcus luteus and Staphylococcus aureus), and fungus (Pichia pastoris). The phagocytic rates of oyster hemocytes towards V. splendidus pre-incubation with rCgC1qDC-6 were significantly enhanced (p < 0.05). In the chemotaxis assay, rCgC1qDC-6 could mediate the migration of oyster hemocytes in a dose-dependent manner, which exhibited a positive chemotactic effect at low concentration (<10 nM). These results collectively indicated that CgC1qDC-6 could serve as a pattern recognition receptor and mediate the hemocyte phagocytosis and migration to eliminate the invading pathogens.