The involvement of CLec-HTM/IgR-Syk-BCL10-mTOR/ERK signaling pathway in immune priming of oysters

Increasing evidence indicates that invertebrates have the immune adaptive abilities, which is commonly known as "immune priming". However, the mechanism of immune priming is believed to be rather complicated, and it has not been fully elucidated. In the present study, in the oysters where the CgCLec-HTM/IgR-Syk-BCL10 signaling pathway was interfered by silencing the expression of the main components, the phosphorylation of mTOR and ERK decreased significantly at 6 h after the first Vibrio splendidus stimulation. The messenger RNA (mRNA) transcript levels of the glycolysis-associated genes (CgGluT and CgGK), NAD+/NADH ratio, lactate concentration, and H3K4me1 and H3K4me3 levels all decreased significantly at 7 d after the first V. splendidus stimulation. Meanwhile, the hemocyte phagocytic rates and the mRNA transcript levels of CgClathrin, CgATPeV, and CgTNF also decreased significantly at 7 d after the first stimulation and 6 h after the second stimulation with V. splendidus. The mRNA transcript levels of CgGluT, CgGK, CgATPeV, and CgTNF; lactate concentration; and H3K4me1 and H3K4me3 levels were all reduced in rapamycin-treated oysters after the first stimulation. The mRNA transcript levels of CgGK, CgClathrin, CgATPeV, and CgTNF; NAD+/NADH ratio; and the levels of H3K4me1 and H3K4me3 were also reduced in FR180204-treated oysters after the first stimulation. These results indicated that the CLec-HTM/IgR-Syk-BCL10-mTOR/ERK signaling pathway regulated histone methylation through mediating the glycolysis to enhance cell phagocytosis and inflammatory response and played a significant regulatory role in the immune priming of Crassostrea gigas, which provided new clues for studying the evolution of immune adaptability.