Differential modulations of two glyceraldehyde 3-phosphate dehydrogenase mRNAs in response to bacterial and viral challenges in a marine teleost Oplegnathus fasciatus (Perciformes)

Glyceraldehyde 3-phosphate dehydrogenase (GAPDH) has been recognized as an invariant internal control for various gene expression studies due to its classical housekeeping role in the glycolytic metabolism. However recently, this enzyme has been proven to be a multifunctional protein involved in diverse non-glycolytic activities. In the present study, two paralogue isoforms of GAPDH mRNAs were characterized from a marine teleost species, rockbream (Oplegnathus fasciatus; Perciformes) and their transcriptional responses to bacterial and viral infections were examined. Rockbream GAPDH1 and GAPDH2 cDNAs encoded 333 and 335 amino acids, respectively, and the amino acid sequence identity between those two isoforms was 74%. Two isoform GAPDH mRNAs were detected ubiquitously in all of tissues examined, but their expression levels were quite variable among tissues. Based on the real-time RT-PCR analysis, the transcription of rbGAPDH1 was affected by neither bacterial (Escherichia coli, Edwardsiella tarda, Vibrio anguillarum or Streptococcus iniae) nor viral (rockbream iridovirus; RBIV) challenges. However on the contrary, the mRNA expression of rbGAPDH2 was significantly up-regulated in liver resulting from the bacterial infections (up to 25-fold), and in both liver (more than sixfold) and kidney (up to fivefold) from the viral infection. Results in the present study suggest that teleost GAPDH isoforms may also be potentially involved in immune modulations especially with respect to inflammatory responses, which is distinct from its classical glycolytic function.