CgBlimp-1 inhibits granulocytes proliferation and interleukin production in the immune response of oyster Crassostrea gigas

Abstract

B lymphocyte-inducible maturation protein 1 (Blimp-1) is a SET domain and zinc fingers containing transcriptional repressor, which is necessary for regulating the development of many immune cell lineages and keeping immune homeostasis. In the present study, a Blimp-1 homologue (designated as CgBlimp-1) was identified from oyster Crassostrea gigas, which contained a conserved SET domain and five ZnF_C2H2 domains and shared high homology with Blimp-1 from other species. The mRNA transcripts of CgBlimp-1 were highly expressed in gill and hepatopancreas. CgBlimp-1 protein was detected to be specifically expressed in granulocytes. After V. splendidus stimulation, the mRNA expression level of CgBlimp-1 in haemocytes up-regulated significantly at 24, 48, and 96 h, which was 4.39-fold (p < 0.05), 7.68-fold (p < 0.01) and 2.65-fold (p < 0.05) of that in control group, respectively. When the expression of CgBlimp-1 was knocked-down in vivo by RNAi, the mRNA expressions of downstream transcription factor CgMyc-A (1.63-fold of that in control group, p < 0.05) and cell cycle related gene CgCDK2 (1.70-fold, p < 0.05) increased significantly at 24 h after V. splendidus stimulation. Concomitantly, the ratio of EdU+ haemocytes increased notably (p < 0.01) while the proportion of haemocytes in G0/G1 phase decreased dramatically (p < 0.001), compared to that in control group. More specifically, the proportion of granulocytes in total haemocytes increased apparently (p < 0.05) in CgBlimp-1-RNAi oysters, together with up-regulation (p < 0.05) of the ratio of EdU+ granulocytes and down-regulation (p < 0.001) of the proportion of granulocytes in G0/G1 phase. Furthermore, the mRNA expression levels of CgIL17-1, CgIL17-2 and CgIL17-4 in haemocytes increased significantly in CgBlimp-1-RNAi oysters, which was 1.71-fold (p < 0.05), 144.70-fold (p < 0.01) and 1.93-fold (p < 0.05) of that in control group, respectively. Aforementioned results suggested that CgBlimp-1 could reduce the proliferation of granulocytes by arresting cell cycle in G1/G0 phase and avoid over-expression of interleukin to maintain homeostasis in the immune response of oyster.