Detailed immunohistology of Pax6 protein and tyrosine hydroxylase in the early zebrafish brain suggests role of Pax6 gene in development of dopaminergic diencephalic neurons

Spatiotemporal developmental dynamics of Pax6 protein containing (i.e., Pax 6) cells were investigated immunohistochemically in embryonic and postembry onic zebrafish brain sections (especially at 2 and 5 day), allowing for a n euroanatomically detailed resolution previously only reported for the mouse . Besides strikingly close correspondences of early Pax6 domains - includin g many spatiotemporal changes - in mouse and zebrafish brains, some critica l differences were noted. There is no pallial (i.e., cortical) Pax6 express ion domain in the ventricular proliferative layer in the zebrafish as in th e mouse. The main pallial Pax6 domain in the zebrafish is comparable to the migrating stream of Pax6 cells at the pallial-subpallial boundary. This in dicates that some developmental functions of Pax6 (i.e., inhibition of subp allial cell migration into pallium by Pax6 migrating stream) might be share d with the mouse and maybe all vertebrates, while others (i.e., control of intrapallial neuronal radial migration via Pax6 expressing radial glia cell s) may be special for mammals. Another prominent feature in the early zebra fish forebrain is that the alar plate ventral thalamic Pax6 domain extends far caudolaterally into the periphery of the basal plate posterior tubercul um and hypothalamic inferior lobe. This indicates that the alar plate ventr al thalamus invades the forebrain basal plate and contributes to the develo pment of basal forebrain structures. The close spatiotemporal association o f Pax6 cells and TH cells of the ventral thalamus indicates a local role of Pax6 in the development of ventral thalamic (as recently demonstrated in t he mouse) and, maybe, posterior tubercular TH cells. However, our confocal microscopical analysis of zebrafish brain sections double-immunostained for Pax6 and TH did not reveal cells double-labeled for these two proteins in this location, but rather indicates an inductive interaction of Pax6 cells onto TH cells. (C) 2001 Elsevier Science B.V. All rights reserved.