Molecular characterization and expression analysis of the IkappaB gene from pearl oyster Pinctada fucata

Inhibitor of NF-kappaB (IkappaB) is one important member of NF-kappaB signal pathway and plays a pivotal role in regulating the innate immune response of invertebrate. Herein, we described the isolation and characterization of pearl oyster Pinctada fucata IkappaB gene (designated as poIkappaB). The poIkappaB cDNA was 1975 bp long and consisted of a 5' untranslated region (UTR) of 73 bp, a 3' UTR of 807 bp with three RNA instability motifs (ATTTA) and a polyadenylation signal (AATAAA) at 13 nucleotides upstream of the poly (A) tail, and an open reading frame (ORF) of 1095 bp encoding a polypeptide of 364 amino acids with an estimated molecular mass of 40.11 kDa and theoretical isoelectric point of 4.61. A conserved degradation motif (DS(35)GFSS(39)) and six ankyrin repeats were identified in the poIkappaB by SMART analysis. Homology analysis of the deduced amino acid sequence of the poIkappaB with other known IkappaB sequences by MatGAT software revealed that the poIkappaB shared 23.5-63.3% similarities with other known IkappaB isoforms. The poIkappaB mRNA was constitutively expressed in all studied tissues with the most abundant mRNA in the haemocyte. The poIkappaB mRNA was up-regulated and increased 4.13- and 5.28-fold after LPS and Vibrio alginolyticus stimulation, respectively. These results suggested that the poIkappaB was a constitutive and inducible acute-phase protein that perhaps involved in the immune defense of pearl oyster.