BrdU-, NeuroD (nrd)- and Hu-studies Reveal Unusual Non-ventricular Neurogenesis in the Postembryonic Zebrafish Forebrain

In the postembryonic zebrafish forebrain, subpial locations of neurogenesis do exist in the early cerebellar external granular layer, and--unusually among vertebrates--in the primordial pretectal (M1) and preglomerular (M2) Anlagen as shown here with 5-bromo-2'-deoxyuridine (BrdU)/Hu-immunocytochemistry and in situ hybridization of neuroD. An intermediate BrdU incubation time of 12-16 h reveals in addition to proliferative ventricularly located cells those in M1 and M2. This BrdU saturation-labeling shows--in conjunction with a Hu-assay demonstrating earliest neuronal differentiation--that proliferating cells in M1 and M2 represent neuronal progenitors. This is demonstrated by single BrdU-labeled and double BrdU-/Hu-labeled cells in these aggregates. Further, expression of NeuroD--a marker for freshly determined neuronal cells--confirms this unusual subpial postembryonic forebrain neurogenesis.