Identification, origin and evidence for retained functionality of two IκBα paralogs in Megalobrama amblycephala

I kappa B alpha plays an essential role in the innate immune response in mammals. We found two functional I kappa B alpha paralogs, originating from the teleost-specific genome duplication, in Megalobrama amblycephala: malK B alpha a and maI kappa B alpha b. Their size (936/933 bp) and structure are highly analogous to known orthologs. mRNA expression was analysed by qPCR in spleen, liver, kidney, intestine and gills. Apart from maI kappa B alpha b in gills (<0.001-fold), both paralogs were constitutively expressed in all tissues. Differential expression was observed in gills (high for maI kappa B alpha a) and liver: maI kappa B alpha a - 2nd lowest (0.47), maI kappa B alpha b - 2nd highest (4.25). Both paralogs (mRNA) were upregulated in liver, spleen and kidney after a bacterial (Aeromonas hydrophila) challenge. In spleen, expressions peaked at 12 h post injection (hpi) (maI kappa B alpha a = 14.3-fold, maI kappa B alpha b = 21.3-fold), but only malKBab was highly upregulated at 4, 24 and 120 hpi. In liver, both were upregulated early, but maI kappa B alpha a peaked at 4 hpi (15.2-fold) and maI kappa B alpha b at 12 hpi (9.8-fold). In kidney, maI kappa B alpha a was highly upregulated only at 12 hpi (8.7-fold), and maI kappa B alpha b at 4 (peak - 8.2-fold), 12 and 24 hpi. The results indicate that both I kappa B alpha paralogs have retained their functionality, that they are structurally and functionally homologous to I kappa B alpha orthologs described in other animal species, and that they both play an important role in the innate immune system of M. amblycephala. (C) 2016 Elsevier Ltd. All rights reserved.