Multiple and highly divergent IL-11 genes in teleost fish.

Interleukin-11 (IL-11) is a key cytokine in the regulation of proliferation and differentiation of hematopoietic progenitors and is also involved in bone formation, adipogenesis, and protection of mucosal epithelia. Despite this prominent role in diverse physiological processes, IL-11 has been described in only four mammalian species, and recently, in rainbow trout (Oncorhynchus mykiss). Here we report the presence of IL-11 in common carp (Cyprinus carpio), a bony fish species related to zebrafish. IL-11 is expressed in most carp organs and tissues. In vitro expression of IL-11 in cultured macrophages is enhanced by stimulation with lipopolysaccharide and is markedly inhibited by cortisol. A detailed and systematic scan of several fish genome databases confirms that IL-11 is present in all fish, but also reveals the presence of a second, substantially different IL-11 gene in the genomes of phylogenetically distant fish species. We designated both fish paralogues IL-11a and IL-11b. Although sequence identity between fish IL-11a and IL-11b peptides is low, the conservation of their gene structures supplemented by phylogenetic analyses clearly illustrate the orthology of both IL-11a and IL-11b genes of fish with mammalian IL-11. The presence of IL-11 genes in fish demonstrates its importance throughout vertebrate evolution, although the presence of duplicate and divergent IL-11 genes differs from the single IL-11 gene that exists in mammals.