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

In this paper the cloning of interleukin-1β (IL-1β) from the fish Dicentrarchus labrax (sea bass) is described. Using degenerate primers designed from known IL-1β 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-1β. 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-1β sequences. Expression studies show that sea bass IL-1β 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-1β 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-1β from other vertebrates is presented.