Molecular characterization, expression, and immunological response analysis of the TWEAK and APRIL genes in grass carp, Ctenopharyngodon idella

TWEAK and APRIL are important members of the TNF superfamily, which play a crucial role in several diseases. Here, we describe the identification of grass carp (Ctenopharyngodon idella) homologs of TWEAK and APRIL (designated gcTWEAK and gcAPRIL, respectively) and their response to Aeromonas hydrophila and Aquareovirus infection. The gcTWEAK cDNA sequence contains 2273 bases with an open reading frame of 753 bases encoding 250-amino acid residues. The gcTWEAK protein contains a predicted transmembrane domain, a putative furin protease cleavage site, 3 conserved cysteine residues, and a typical TNF homology domain. The gcAPRIL cDNA sequence contains 1408 bases with an open reading frame of 747 bases encoding 248-amino acid residues. The gcAPRIL protein contains a predicted transmembrane domain, a putative furin protease cleavage site, 2 conserved cysteine residues, and a typical TNF homology domain corresponding to other, known APRIL homologs. Reverse transcription-polymerase chain reaction analysis shows that both gcTWEAK and gcAPRIL transcripts are predominantly expressed in the skin, spleen, and head kidney, and they are significantly upregulated in most immune tissues by A. hydrophila and Aquareovirus infections. Our results demonstrate that liver is the most responsive tissue against bacterial infection, whereas gill is the most responsive tissue against viral infection. The association of increased gcTWEAK and gcAPRIL expression after bacterial and viral infections suggests that they play a potentially important role in the immune system of fish.