Two NF-κB inhibitor-alpha (IκBα) genes from rock bream (Oplegnathus fasciatus): Molecular characterization, genomic organization and mRNA expression analysis after immune stimulation

• As in other vertebrates, both rock bream IκBα (OfIκBαA and OfIκBαB) genes possess 6 exons.
• OfIκBα proteins feature the typical domain characteristics of IκBα proteins.
• With constitutive expression, highest mRNA level of OfIκBα is found in heart and liver.
• Flagellin-injection significantly modulated the transcription of OfIκBα in 5 tissues.
• OfIκBαs′ regulated expression upon immune challenges implies their role in immunity.

IκBα is a member of IκB family, which sequesters NF-κB in an inactivate form in the cytoplasm and blocks the translocation of NF-κB to nucleus. The IκBα paralogs of rock bream (OfIκBα-A and OfIκBα-B) encoded IκBα proteins with typical features including, highly conserved IκB degradation motif, six ankyrin repeats and a PEST sequence. However, their amino acid identity and similarity were only 55.6 and 69.7%, respectively suggesting that these two genes could be the two different isoforms of IκBα. The number and size of the exons of OfIκBα-A and OfIκBα-B were conserved well with all the compared vertebrate species, although they have significantly different genomic sizes. Phylogenetic analysis revealed that OfIκBα-A and OfIκBα-B proteins cluster with IκBα family members; however, they were grouped with different subclades in IκBα family. Tissue specific expression of OfIκBα mRNA was constitutively detected in all the tested tissues, and they showed the higher transcription level in heart, liver, gill and peripheral blood cells, respectively. The injection of flagellin stimulated the mRNA expression of OfIκBα paralogs in head kidney and intestine. Moreover, the OfIκBα mRNA expression in gill and liver was significantly up-regulated by LPS, poly I:C and Edwardsiella tarda challenges. The transcription of OfIκBα was up-regulated in early-phase of injection and then rapidly restored. These results suggest that the OfIκBα paralogs might be involved in rapid immune responsive reactions in rock bream against bacterial and viral pathogens.