DECIPHERING OF MOLECULAR CHARACTERS AND IMMUNE RELATED FUNCTIONS OF TWO AKIRIN2 HOMOLOGUES FROM BIG BELLY SEAHORSE (Hippocampus abdominalis).  

Akirins are highly conserved nuclear localized proteins present throughout metazoan. Most of the vertebrate species have two homologs of akirin genes. In vertebrates, akirin2 is required downstream of NF-Kb in toll-like receptor (TLR), tumour necrosis factor (TNF) and interleukin (IL)-1β signaling pathways for the production of inflammatory cytokines such as IL-6. In the present study, two homologs of seahorse akirin2 gene were identified from transcriptome database of seahorse and designated as Haakirin2(1) and Haakirin2(2). The molecular features of Haakirin2(1) and Haakirin2(2) were studied using bioinformatics tools. The spatial distribution, and transcriptional modulation during the immune challenges (LPS, Poly I:C and Streptococcus iniae ) were determined in liver and kidney tissues by using qPCR.

The Open Reading Frame (ORF) of Haakirin2(1) cDNA was consisted of 543 bp which encoded for 180 amino acids with estimated molecular weight (MW) of 20.48 kDa. Meanwhile, 537 bp long ORF was identified from Haakirin2(2) which encoded for 178 amino acids with MW of 20.46 kDa. No putative conserved domain was detected from seahorse akirin2 homologs during the in silico analysis. Phylogenetic tree showed a closer relationship of Haakirin2(1) and Haakirin2(2) with respective orthologs from fish species belongs to Acanthopterygian taxa.

Tissues dependent relative mRNA expression of Haakirin2(1) and Haakirin2(2) showed that both homologs in seahorse were ubiquitous in all tissues with higher expression from ovary. During the temporal analysis, in kidney, HaAkirin2(1) showed a significant early up-regulation throughout all challenges. In contrast, the liver tissue showed a significant up-regulation of Haakirin2(1) in late phase of the challenges. Meanwhile, Haakirin2(2) homolog was showed an up-regulated expression after 12h post injection in liver. In kidney, Haakirin2(2) was significantly up-regulated in the mid phase of immune challenges. The results suggest that seahorse akirin2 homologs play a critical role in defense against bacterial and viral pathogens.