Alternative splicing and immune response of Crassostrea gigas tumor necrosis factor receptor-associated factor 3.

Diverse alternative splicing isoforms play an important role in immune diversity and specificity. Their role in molluscan host-defense is however poorly understood. We characterized two alternative isoforms of tumor necrosis factor receptor-associated factor 3 (TRAF3) in the Pacific oyster, Crassostrea gigas, which were named CgTRAF3-S and CgTRAF3-L. An intron was retained in CgTRAF3-L, introducing a premature termination codon. Comparison and phylogenetic analysis revealed that CgTRAF3 shared a higher identity with other species, suggesting the conservation of the two gene transcripts. Quantitative real-time PCR was performed and the expression levels of CgTRAF3 isoforms were found to be significantly changed after Vibrio anguillarum and ostreid herpesvirus 1 challenges. These two isoforms represented contrary trends, indicating that CgTRAF3-L might function as a negative regulator of CgTRAF3-S. We also investigated the expression level of the transcripts of the two CgTRAF3 isoforms, following the silence of C. gigas mitochondrial anti-viral signaling protein like gene (CgMAVS-like). We concluded that CgTRAF3 might be involved in a MAVS-mediated immune signaling pathway. This study suggests that CgTRAF3 may be a response to bacterial and viral stimulation and that the two isoforms may be involved in immune response pathways. It is also possible that the two alternative splicing isoforms could be inter-coordinated and may promote survival of these oysters under immune stress conditions.