Immune response and biomarker transport roles of extracellular vesicles in marine mollusk species

Understanding the immune systems of oysters and clams is important in monitoring the effects of pollution and climate change on the health of molluscan species and the potential impacts on the aquaculture industry. Their immune responses also can serve as indicators of changes in ocean environments.

A new study involving the University of Maine assessed immune responses in four economically important marine mollusc species — the blue mussel, soft-shell clam, Eastern oyster, and Atlantic jackknife clam — and identified new biomarkers relating to changes in protein function involved in novel regulatory mechanisms of important metabolic and immunological pathways.

The discovery will aid further biomarker identification to benefit the aquaculture industry and provides new understanding of how these pathways function in diverse ways in different animal species.

“These biomarkers reveal how several different physiological functions can be generated from a single protein sequence. This gives added value to an organism’s physiology,” says Tim Bowden, UMaine associate professor of aquaculture and co-author of the study published as the cover article in the December 2020 issue of the journal Biology.

Study findings suggest that the enzymes that regulate deimination in mammals, birds and reptiles, and bacteria, parasites and fungi also are active in molluscan pathways. Peptidylarginine deiminases, or PADs, which had not previously been reported in Mollusca, may in fact serve as a control switch for varied immune and metabolic pathways in Mollusca and across the phylogenetic tree, according to the research team.

 Transmission electron microscopy (TEM) analysis of Mollusca hemolymph EVs

(A) Blue mussel; (B) soft shell clam; (C) Eastern oyster; (D) Atlantic jacknife clam. (E) Western blotting (WB) of hemolymph EVs (representative figure showing EVs from soft Atlantic jacknife clam) shows strong CD63 positive (protein size standard is indicated in kilodaltons, kDa).

The researchers documented species-specific variations in the size and distribution of extracellular vesicles (EVs) in the bivalves studied. EVs have multiple functions including transporting proteins, genetic cargoes and biomarkers into cells and mediating host-pathogen interactions, among others.

Further investigation of the physiological and immune-related roles of EVs and characterization of the biomarkers they transport is warranted to enhance understanding of regulatory mechanisms and pathways in Mollusca and to support the global aquaculture industry.

Source – University of Maine

Bowden TJ, Kraev I, Lange S. (2020) Extracellular Vesicles and Post-Translational Protein Deimination Signatures in Mollusca-The Blue Mussel (Mytilus edulis), Soft Shell Clam (Mya arenaria), Eastern Oyster (Crassostrea virginica) and Atlantic Jacknife Clam (Ensis leei). Biology (Basel) 9(12):416. [article]

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