In the adult teleost brain, proliferating cells are observed in a broad area, while these cells have a restricted distribution in adult mammalian brains. In the adult teleost optic tectum, most of the proliferating cells are distributed in the caudal margin of the periventricular gray zone (PGZ). We found that the PGZ is largely divided into 3 regions: 1 mitotic region and 2 post-mitotic regions-the superficial and deep layers. These regions are distinguished by the differential expression of several marker genes: pcna, sox2, msi1, elavl3, gfap, fabp7a, and s100beta. Using transgenic zebrafish Tg (gfap:GFP), we found that the deep layer cells specifically express gfap:GFP and have a radial glial morphology. We noted that bromodeoxyuridine (BrdU)-positive cells in the mitotic region did not exhibit glial properties, but maintained neuroepithelial characteristics. Pulse chase experiments with BrdU-positive cells revealed the presence of self-renewing stem cells within the mitotic region. BrdU-positive cells differentiate into glutamatergic or GABAergic neurons and oligodendrocytes in the superficial layer and into radial glial cells in the deep layer. These results demonstrate that the proliferating cells in the PGZ contribute to neuronal and glial lineages to maintain the structure of the optic tectum in adult zebrafish.
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