Fish antiviral tripartite motif (TRIM) proteins

Tripartite motif (TRIM) family or RBCC proteins comprises characteristic zinc-binding domains (a RING (R), a B-box type 1 (B1) and a B-box type 2 (B2)) and coiled-coil (CC) domain followed by a C-terminus variable domain. There are about 80 different TRIM proteins in human, but more than 200 in zebrafish with several large gene expansions (ftr > 70 genes; btr > 30 genes; trim35 > 30 genes). Repertoires of trim genes in fish are variable across fishes, but they have been remarkably diversified independently in a number of species. In mammals, TRIM proteins are involved in antiviral immunity through an astonishing diversity of mechanisms, from direct viral restriction to modulation of immune signaling and more recently autophagy. In fish, the antiviral role of TRIM proteins remains poorly understood. In zebrafish, fish specific TRIMs so called fintrims show a signature of positive selection in the C terminus SPRY domain, reminding features of mammalian antiviral trims such as TRIM5. Expression studies show that a number of trim genes, including many fintrims, can be induced during viral infections, and may play a role in antiviral defence. Some of them trigger antiviral activity in vitro against DNA and RNA viruses, such as FTR83 that also up-regulates the expression of type I IFN in zebrafish larvae. The tissue distribution of TRIM expression suggests that they may be involved in the regionalization of antiviral immunity, providing a particular protection to sensitive areas exposed to invading pathogens.