CgMyD88s Serves as an Innate Immune System Plug During Ostreid Herpesvirus 1 Infection in the Pacific Oyster (Crassostrea gigas).

Xueying Tang,Siheng Lin,Baoyu Huang,Li Li,Wei Wang,Guofan Zhang

doi:10.3389/fimmu.2020.01247

Abstract

Ostreid herpesvirus-1 microvariant (OsHV-1 μVar) is considered a major infectious microbe that can reduce the survival of natural or cultured oysters in summer. Because they lack an adaptive immune system, oysters are dependent on their innate immune systems to fight pathogens. The duplication and functional divergence of innate immune genes in the oyster have been studied, but the contribution of molecular mechanisms underlying innate immunity remains to be defined. Here, we identified the interacting proteins associated with Crassostrea gigas Toll-like receptors (CgTLR) using a yeast two-hybrid (Y2H) screening system. A total of eight proteins were identified that could interact with CgTLR. Three of these appeared at least four times in the screening and were related to MyD88. Two genes encoding these MyD88-like proteins, CgMyD88-1 and CgMyD88-2, possessed typical death and TIR domains. The third gene encoding an MyD88-like protein possessed only a TIR domain, and we named it CgMyD88s. CgMyD88s interacted only with CgTLR, but not CgMyD88-1 or CgMyD88-2. Both CgMyD88-1 and CgMyD88-2 mRNAs were upregulated after OsHV-1 μVar infection, whereas the expression of CgMyD88s decreased. When overexpressed in HEK293T cells, CgMyD88-1 and CgMyD88-2 activated an NF-κB reporter, whereas CgMyD88s impaired activation induced by CgMyD88-1 or CgMyD88-2. Intriguingly, the silencing of CgMyD88s using double-stranded RNA (dsRNA)-mediated RNA interference increased the expression of CgMyD88-1 and CgMyD88-2. Taken together, our results revealed that CgMyD88-1, CgMyD88-2, and CgMyD88s may all participate in the TLR-mediated innate immune pathway and that CgMyD88s served as a plug to avoid oysters from excessive inflammatory response during OsHV-1 μVar infections.

Highlights

Bivalves include clams, mussels, scallops, and oysters, and some of these, such as cultured Pacific oyster (Crassostrea gigas), are of great economic importance
Using Y2H system, we found that just Cg27513-Toll-like receptor (TLR) could interact with both CgMyD88-1 and CgMyD88-2 (Figure 1C)
Results showed that expression of CgMyD88-1 was significantly upregulated beginning at 48 h after interference and decreased slowly, whereas CgMyD88-2 expression was upregulated beginning at 72 h and declined rapidly (Figures 7B,C)

Summary

Introduction

Mussels, scallops, and oysters, and some of these, such as cultured Pacific oyster (Crassostrea gigas), are of great economic importance. The Pacific oyster, originally found only in East Asia, has been successfully introduced into many countries and has become a major aquaculture species worldwide, because C. gigas can tolerate harsh and dynamically changing environments [1, 2]. Most natural and many cultured oyster populations experience mass mortality events, especially in summer [3]. Summer oyster mortality is the consequence of complex interactions between the hosts, environment, and pathogens [4,5,6]. Especially ostreid herpesvirus 1 (OsHV-1), infect bivalve species in the aquaculture industry [7,8,9,10]. An OsHV-1 microvariant, μVar, appeared during the summer of 2008 in France and seems to be the dominant herpesvirus that infects these oysters [8, 11]. Upon PAMP recognition, hosts initiate intracellular signaling, which uses adaptors, kinases, and transcription factors to trigger proinflammatory and antimicrobial effectors [16]

Methods

Results

Conclusion