Cxcr4 and Cxcl12 expression in radial glial cells of the brain of adult zebrafish.

Unlike that of mammals, the brain of adult teleost fish exhibits an intense and widespread neurogenic activity as a result of the persistence of radial glial cells acting as neural progenitors throughout life. Because chemokines, notably CXCL12, and their receptors, such as CXCR4, play key roles in mammalian embryonic neurogenesis, we investigated Cxcr4 and Cxcl12 expressions in the brain of adult zebrafish and their potential relationships with cell proliferation. Cxcr4 expression was found to be restricted to radial glial cells in the adult zebrafish, where it is co-expressed with established radial glial cell markers, such as brain lipid-binding protein (Blbp) or the estrogen-synthesizing enzyme aromatase B (Cyp19a1b). Double stainings combining proliferating cell nuclear antigen (PCNA) and Cxcr4 immunolabelling indicated that there is no obvious association between Cxcr4 expression and radial glial cell proliferation. Interestingly, cxcl12a messengers were detected in ventricular regions, in cells corresponding to aromatase B-immunoreactive radial glial cells. Altogether, our data demonstrate Cxcl12 and Cxcr4 expression in radial glial cells of the brain of adult zebrafish, supporting important roles for the Cxcl12/Cxcr4 pair in brain development and functioning.