Evolutionary evidence of tumor necrosis factor super family members in the Japanese pufferfish (Takifugu rubripes): Comprehensive genomic identification and expression analysis

Abstract

Tumor necrosis factor (TNF) and its superfamily (TNFSF) members are important inflammatory cytokines. Although fish have fourteen TNFSF genes, their genomic location and existence are yet to be described and confirmed in the Japanese pufferfish (Fugu) (Takifugu rubripes). Therefore, we conducted in silico identification, synteny analysis of TNFSF genes from Fugu with that of zebrafish and human TNFSF loci and their expression analysis in various tissues. We identified ten novel TNFSF genes, viz. TNFSF5 (CD40L), TNFSF6 (FasL), three TNFSF10 (TRAIL) (-1, 2 and 3), TNFSF11 (RANKlg), TNFSF12 (TWEAK), two TNFSF13B (BAFF) (1 and 2) and TNFSF14 (LIGHT) belonging to seven TNFSFs in Fugu. Several features such as existence of TNF family signature, conservation of genes in TNF loci with human and zebrafish chromosomes and phylogenetic clustering with other teleost TNFSF orthologs confirmed their identity. Fugu TNFSF genes were constitutively expressed in all eight different tissues with most of them expressed highly in liver. Fugu TNFSF10 gene has three homologs present on chromosomes 10 (TNFSF10-1), 8 (TNFSF10-2) and 2 (TNFSF10-3). Moreover, a phylogenetic analysis containing all available vertebrate (mammals, birds, reptiles, amphibians and fish) TNFSF10 orthologs showed that Fugu TNFSF10-1 and 10-3 are present in all vertebrates, whereas TNFSF10-2 was not related to any mammalian and avian orthologs. Viral double-stranded RNA mimic poly (I:C) caused an elevated expression of three Fugu TNFSF10 genes in head kidney cells at 4h indicating probable role of these genes to induce apoptosis in virus-infected cells. In conclusion, Fugu possesses genes belonging to nine TNFSFs including the newly identified seven and previously reported two, TNFSF New (TNF-N) and TNFSF2 (TNF-α). Our findings would add up information to TNFSF evolution among vertebrates.

Keywords: Genomic location; Japanese pufferfish; TNFSF evolution; TNFSF10; Tumor necrosis factor superfamily.