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Published on: June 11, 2020
A C1qDC (CgC1qDC-6) with a collagen-like domain mediates hemocyte phagocytosis and migration in oysters
Huan Li1, Ning Kong1, Jiejie Sun1
1Liaoning Key Laboratory of Marine Animal Immunology, Dalian Ocean University, Dalian, 116023, China; Liaoning Key Laboratory of Marine Animal Immunology and Disease Control, Dalian Ocean University, Dalian, 116023, China; Dalian Key Laboratory of Aquatic Animal Disease Prevention and Control, Dalian Ocean University, Dalian, 116023, China.
Insights
Pacific oysters possess a novel immune protein, CgC1qDC-6, that recognizes pathogens and enhances immune cell activity. This finding reveals a new mechanism for invertebrate immunity and pathogen defense.
Area of Science:
- Marine Biology
- Immunology
- Biochemistry
Background:
- Bivalve C1q domain-containing proteins (C1qDCs) typically lack collagen regions, unlike their vertebrate counterparts.
- Understanding novel immune molecules in bivalves like the Pacific oyster (Crassostrea gigas) is crucial for aquaculture and marine ecosystem health.
Purpose of the Study:
- To identify and characterize a novel C1qDC from Crassostrea gigas, designated CgC1qDC-6, with a collagen-like domain.
- To investigate the potential role of CgC1qDC-6 in the immune responses of the Pacific oyster.
Main Methods:
- Bioinformatic analysis and gene sequencing of CgC1qDC-6.
- Expression analysis of CgC1qDC-6 at mRNA and protein levels across various oyster tissues.
- In vitro assays using recombinant CgC1qDC-6 (rCgC1qDC-6) to assess binding to pathogen-associated molecular patterns (PAMPs) and microorganisms.
- Functional assays including hemocyte phagocytosis and chemotaxis experiments.
Main Results:
- CgC1qDC-6 possesses a unique structure with N-terminal signal peptide, central collagen-like domain, and C-terminal ghC1q domain.
- CgC1qDC-6 is expressed in all tested tissues, including hemocytes, suggesting a systemic immune role.
- rCgC1qDC-6 demonstrated binding to various PAMPs (LPS, PGN, mannose, Poly I:C) and pathogens (bacteria, fungi).
- rCgC1qDC-6 significantly enhanced hemocyte phagocytosis of Vibrio splendidus and mediated dose-dependent hemocyte migration.
Conclusions:
- CgC1qDC-6 functions as a pattern recognition receptor in the Pacific oyster.
- CgC1qDC-6 plays a vital role in innate immunity by promoting hemocyte-mediated phagocytosis and chemotaxis against invading pathogens.
Abstract:
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.
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