Phylogeny of cytokines: molecular cloning and expression analysis of sea bass Dicentrarchus labrax interleukin-1b

Abstract

In this paper the cloning of interleukin-1b (IL-1b) from the fish Dicentrarchus labrax (sea bass) is described. Using degenerate primers designed from known IL-1b sequences, a cDNA fragment was amplified by PCR and elongated by 3’ and 5’ RACE to give the full-length coding sequence for sea bass IL-1. The cDNA is 1292 bp, lacks a putative ICE cut site, and codes for a deduced peptide of 29.4 kDa with a pI of 5.1. Sequence analysis showed highest amino acid similarity with rainbow trout (62%), Xenopus (46%), and carp (45.5%) IL-1b sequences. Expression studies show that sea bass IL-1b can be upregulated by bacterial lipopolysaccharide both in vitro and in vivo in leucocytes from blood, head-kidney, spleen, gills and liver, whereas the IL-1b transcript was not detectable in thymus and gut-associated lymphoid tissue. Northern blot analysis with head-kidney leucocyte RNA showed a main LPS- upregulated band at 1.3 kb, and two minor bands at 0.9 and 3.0 kb, respectively. Phylogenetic comparisons with IL-1b from other vertebrates is presented.