Tumor necrosis factor-alpha (TNF-α) in spotted halibut Verasper variegatus at the embryonic and metamorphic stages

Abstract

As an aquatic fish, the spotted halibut Verasper variegatus is highly susceptible to bacterial and virus infections. Tumor necrosis factor-alpha (TNF-α) as a cytokine could control the inflammatory responses. The functions of TNF-α in many species have been widely studied, particularly in mammals. However, little is known about the TNF-α functions in V. variegatus. We first cloned and sequenced the TNF-α gene in V. variegatus (VvTNF-α). The two conserved cysteine residues, transmembrane sequence, Thr-Leu motif, and TNF family signature, as well as the TA-rich motifs of its proteins related to inflammatory responses had high similarity to those of the other teleost and mammalian TNF-α. The phylogenetic analysis showed that VvTNF-α was consistent with TNF-α genes of other vertebrates. The VvTNF-α transcripts were extensively distributed in the peripheral blood leukocytes (PBLs), spleen, and gill, indicating that the VvTNF-α had a role in immune function. Furthermore, treatment with pathogen-associated molecular patterns (PAMPs) could induce a rapid and significant increase of VvTNF-α in the PBLs, which reveals that VvTNF-α does participate in the host immune responses against bacterial and viral pathogens. We found that VvTNF-α had an interesting expression pattern during metamorphosis, showing that the flatfish TNF-α may have some novel functions during specific developmental stages. In addition, the 3D structure prediction of VvTNF-α provided an indication of how it is likely to interact with other proteins. Therefore, VvTNF-α has multiple functions, and provides valuable information to explore novel functions of TNF-α.