Exosome-derived small non-coding RNAs reveal immune response upon grafting transplantation in pearl oysters

Exosomes, a subset of small extracellular vesicles, carry various nucleic acids, proteins, lipids, amino acids and metabolites. They function as a mode of intercellular communication and molecular transfer. Exosome cargo molecules, including small non-coding RNAs (sncRNAs), are involved in the immune response in various organisms. However, the role of exosome-derived sncRNAs in immune responses in molluscs remains unclear.

Researchers at the University of Tokyo aimed to reveal the sncRNAs involved in the immune response during grafting transplantation by the pearl oyster Pinctada fucata. Exosomes were successfully extracted from the P. fucata haemolymph during graft transplantation. Abundant microRNAs (miRNAs) and PIWI-interacting RNAs (piRNAs) were simultaneously discovered in P. fucata exosomes by small RNA sequencing. The expression patterns of the miRNAs and piRNAs at the grafting and initial stages were not substantially different, but varied significantly between the initial and later stages. Target prediction and functional analysis indicate that these miRNAs and piRNAs are related to immune response upon grafting transplantation, whereas piRNAs may also be associated with transposon silencing by targeting with genome transposon elements. This work provides the basis for a functional understanding of exosome-derived sncRNAs and helps to gain further insight into the PIWI/piRNA pathway function outside of germline cells in molluscs.

Small RNAs identified in Pinctada fucata exosome

(a) Experimental design for mantle grafting and sampling schedule; (b) length distribution of clean reads by small RNA sequencing during mantle grafting; (c) principal component analysis of miRNA expression patterns in P. fucata exosome during mantle grafting; (d) Venn diagram of the overlap of known miRNA profiles and conserved miRNA family in P. fucata and related species. (e) Heatmap of identified miRNA expression patterns in all investigated samples of P. fucata. PA, just after grafting.