Characterization of an interleukin-15 like (IL-15L) gene from zebrafish (Danio rerio)

In fish, interleukin (IL)-2, IL-21 and IL-15 genes have recently been identified by in-silico cloning. Fish IL-15 gene is similar to counterparts from mammals and other vertebrates. A zebrafish genomic database-search initiated to find IL-2 and IL-21 genes from zebrafish (Danio rerio) led to the identification of an IL-15 like gene (IL-15L). This gene was cloned by prediction and the transcripts were subsequently cloned by PCR. The predicted translation yielded a 162 amino acid protein with a 42 amino acid-long signal peptide. This protein shared identities of 28.4% to 31.5% with other mammalian and vertebrate IL-2, IL-15 and IL-21 genes. The gene occupies 7.7 kb of the genomic DNA and the coding region spans into four exons and is interrupted by three introns, which is similar to the genomic structure of IL-2 gene. The chromosomal synteny and phylogenetic analyses support our view that this IL-15L gene is specific to teleosts. Furthermore, two alternatively spliced forms have been identified with differential exon usage translating for proteins of 108 and 120 amino acids in length. The analysis of the alternative splicing suggests it may play an important role in regulating the function of this novel gene. Analyses by RT-PCR and in situ hybridization show gene expression in lymphoid tissues like intestine, gills, spleen, pancreas and kidney suggestive of a role in immunity of fish.