Structural diversity and function of the granulocyte colony-stimulating factor in medaka fish

•Medaka granulocyte colony-stimulating factor (G-CSF) is predicted to have similar tertiary structures of human G-CSF.•G-CSF regulates granulopoiesis in medaka.•G-CSF promotes the mobilization of neutrophils into the peripheral blood in medaka.•G-CSF-deficient medaka showed low erythrocyte count in the kidney. Diversity in the granulocyte repertoire, including neutrophils, basophils, and eosinophils, has been reported in vertebrate species. Medaka fish (Oryzias latipes) have only neutrophils; however, the storage pool of granulopoiesis tissues and the molecular mechanism of granulopoiesis in medaka fish have not been explored. Granulocyte colony-stimulating factor (G-CSF) is a cytokine responsible for neutrophil differentiation, survival, and proliferation. We performed in silico analysis to molecularly characterize the medaka G-CSF and G-CSF receptor (G-CSFR) genes. This study showed that medaka G-CSF differs considerably from human and mouse G-CSF in terms of the primary protein structure; however, the predicted tertiary structure was largely conserved. Analyses of lipopolysaccharide stimulation and G-CSF knockout and overexpression in medaka revealed that G-CSF mobilizes neutrophils into the peripheral blood. The analysis of G-CSF-deficient medaka revealed that G-CSF is involved in erythropoiesis. These findings represent an important first step toward understanding granulocyte hematopoiesis in nonmammalian species. [Display omitted]