Structure, Evolution And Expression Analysis Of Akirin And LEAP-2 Genes In Fish

As an evolutionarily older defense strategy, the innate immune is the dominant immune system and provides a first line of antimicrobial host defense in teleost. Akirin and LEAP-2 are critical molecules of the innate immune system and play a very important role in resistance against bacterial infections.Akirins, highly conserved nuclear proteins, are present throughout the metazoan and regulate innate immunity, embryogenesis, myogenesis, and carcinogenesis. In this study, we identified all Akirin genes from miiuy croaker and conducted the comprehensive analysis of Akirin gene family in combination with Akirin genes from other species. A second NLS was present in Akirin2 homologues but it was not in Akirin1 homologues in all teleosts, so it may enhance the nuclear import of Akirin2 proteins compared to Akirin1 in all teleosts. Meanwhile, the loss of second NLS in Akirin1 homologues in teleosts may be caused by genome duplication occurred in the teleost lineage. Significantly, Akirin2(2) had six exons interrupted by five introns in miiuy croaker, which may be caused by the intron insertion event and stands as a novel evidence for the variation of Akirin genes structure in some species. In addition, comparison of the genomic neighborhood genes of Akirin1, Akirin2(1) and Akirin2(2) demonstrates a strong level of conserved synteny across the teleost classes, which further proved the deduction of Macqueen and Johnston that the produce of Akirin paralogues can be attributed to whole-genome duplications and the loss of some Akirin paralogues after genome duplications. Akirins acted in concert with the Relish protein induce the expression of a subset of downstream pathway elements(including LEAP-2) in the NF-κB dependent signaling pathway. So we also identified LEAP-2 from miiuy croaker, which contained signal peptide, prodomain and mature peptide. The result of evolutionary analysis indicated that no positive selection exists in LEAP-2 gene sequences, which may be on account of irreplaceable function constrains. Akirin gene family members, Relish and LEAP-2 gene were ubiquitously expressed in all tissues and their expression levels were increased after infection with Vibrio anguillarum in three immune tissues. The expression levels of Akirin genes, Relish and LEAP-2 gene in liver, spleen and head kidney were found first up-regulated and then down-regulated, and finally recovery to normal lever after infection with V. anguillarum. An intricate network of co-regulation were established among Akirin gene family members, Relish and LEAP-2 and it is further proved that Akirins acted in concert with the Relish protein induce the expression of a subset of downstream pathway elements(LEAP-1 and LEAP-2) in the NF-κB dependent signaling pathway.