The chicken proinflammatory cytokines interleukin-1(beta) and interleukin-6: differences in gene structure and genetic location compared with their mammalian orthologues

The genes encoding the chicken proinflammatory cytokines interleukin (IL)-1B and IL-6 were cloned, sequenced and mapped. The exon:intron structure of the coding region of chicken IL1B corresponds almost exactly to those of mammalian IL1B. As yet, we have no evidence for a 5ʹ-UTR non-coding exon equivalent to that found in mammalian IL1B. The exon:intron structure of chicken IL6 differs from those of mammalian IL6, having one exon fewer (the first two exons in mammalian IL6 genes appear to be fused in the chicken gene). We were unable to clone or sequence the promoter of chicken IL1B. The chicken IL6 promoter shares a number of potential regulatory sequences similar to those found in the human IL6 promoter. These putative elements include (5ʹ3ʹ) a glucocorticoid response element (GRE), an AP-1 binding site, an NF-IL-6 binding site (albeit in the reverse orientation), an NF-(kappa)B binding site, a second AP-1 binding site and a TATAAA box. A further GRE, a cAMP response element and regions with homology to c-fos serum responsive elements or retinoblastoma control elements were absent. Promoter sequence polymorphisms were not identified in eight different inbred chicken lines. A restriction single-stranded conformational polymorphism was identified which enabled chicken IL1B to be genetically mapped to one end of chromosome 2. Chicken IL6 was mapped by fluorescent in situ hybridization also to chromosome 2, at an FLpter of 0.26.