Molecular cloning and characterization of interferon regulatory factor 1 (IRF-1), IRF-2 and IRF-5 in the chondrostean paddlefish Polyodon spathula and their phylogenetic importance in the Osteichthyes.

The interferon regulatory factor (IRF) with its 10 members is a very important gene family related to innate immunity. Currently, most fish IRFs reported are from bony fish (teleosts). Cloning and sequencing of IRFs from chondrosteans, the so-called "ancient fish" including sturgeon, paddlefish, bichir and gar, are absent from the literature. In this study, three IRF genes PsIRF-1, PsIRF-2 and PsIRF-5, were cloned and characterized from the paddlefish (Polyodon spathula). PsIRF-1 includes an open reading frame (ORF) of 972 bp that encodes a putative protein of 324 amino acids; PsIRF-2 includes an ORF of 1023 bp encoding 341 amino acids and PsIRF-5 includes an ORF of 1491 bp that encodes 497 amino acids. The PsIRF-5 gene structure is similar to those in mammals but differs from those in teleosts in the first and second exons. Phylogenetic studies of the putative amino acid sequences of PsIRF-1, PsIRF-2 and PsIRF-5 based on the neighbor-joining and Bayesian inference method for Osteichthyes found widely accepted inter-relationships among actinopterygians and tetrapods. Reverse Transcription Polymerase Chain Reaction (RT-PCR) analysis of PsIRF-1, PsIRF-2 and PsIRF-5 in different paddlefish tissues shows higher levels of expression in gill, spleen and head kidney. Poly (I: C) (polyinosinic-polycytidylic acid) stimulation in vivo up-regulated PsIRF-1 and PsIRF-2 expression, while PsIRF-5 gene expression did not respond to the challenge of Poly (I: C).