Molecular Cloning, Characterization, and Expression of Two Myeloid Differentiation Factor 88 (Myd88) in Pacific Oyster, Crassostrea gigas

Abstract

AbstractMyeloid differentiation factor 88 (MyD88) is a universal adaptor protein and plays an important role in the signal transduction of Toll/interleukin‐1 receptor (TIR/IL‐1R) family. In this study, two novel molluskan MyD88 family members (named as CgMyD88‐1 and CgMyD88‐2) were identified from the Pacific oyster, Crassostrea gigas. The full‐length cDNA of CgMyD88‐1 was of 2453 base pairs (bp), with an open reading frame (ORF) of 1077 bp encoding 358 amino acids. The cDNA of CgMyD88‐2 consists of 1374 bp ORF encoding 457 amino acids. Both CgMyD88s contain death domain (DD) and TIR domain which are typical features of MyD88 family proteins. Three conserved boxes were also found in the two CgMyD88s which were similar to MyD88s in vertebrates. The expression level of both CgMyD88 mRNAs in selected tissues was measured by quantitative real‐time polymerase chain reaction (qRT‐PCR). Both CgMyD88 transcripts were constitutively expressed in all tested tissues. Gill and hemocytes were shown with highest expression levels while adductor muscle and gonad were with lower levels. The CgMyD88 transcripts in hemocytes after ostreid herpesvirus 1 (OsHV‐1) challenge were also determined by qRT‐PCR. Both CgMyD88s were significantly upregulated in hemocytes after OsHV‐1 challenge and had significant differences (P < 0.05) at some time points compared with the control. Our results as previously reported suggest that MyD88‐dependent pathway exists in C. gigas, and its critical adaptor CgMyD88 plays important roles in oysters' innate immune defense against OsHV‐1 infection.