A GRANULOCYTE COLONY-STIMULATING FACTOR (G-CSF) IN TELEOST

¹ Laboratory of Genome Science, Graduate School of Marine Science and Technology, Tokyo University of Marine Science and Technology, Konan 4-5-7, Minato-ku, Tokyo 108-8477, Japan

Granulocyte colony-stimulating factor (G-CSF), a cytokine, plays crucial roles in neutrophil proliferation, survival and maturation. First discovered in the 1960s, it is now well studied in humans and veterinary animals due in part to its established clinical importance. However, isolating it in lower vertebrates e.g. teleosts has proven to be very elusive. Here, we isolated and characterized the first G-CSF cDNA in an economically important fish, Japanese flounder (Paralichthys olivaceus). Its full cDNA length is 1,567 bp with an open reading frame (ORF) of 633 bp coding for 211 putative amino acids. Its predicted protein has a molecular mass of about 21 kDa and a signal peptide of 21 aa. BLASTx search showed that it is homologous with known mammalian G-CSFs with a comparative mean homology value of about 21% and is closely related with other cytokines as revealed by phylogenetic analysis using neighbor joining method. Its mRNA is highly expressed in the spleen, and moderately expressed in brain, gills, kidney, peripheral blood leukocytes (PBL) and skin tissues taken from healthy individuals. Expression of its mRNA in kidney and PBLs were up-regulated following treatment of immunostimulants- lipopolysaccharide (LPS), concanavalin A (Con A) and phorbol myristate acetate (PMA). This hematopoietic growth factor, as shown by Southern hybridization, exists as a single copy gene. This study which establishes the presence of G-CSF in fish, adds to our knowledge of fish innate immunity, and allows for future studies that could potentially provide solutions to some of the fish health problems of the aquaculture industry.