Proliferation pattern changes in the zebrafish brain from embryonic through early postembryonic stages

Proliferating cell nuclear antigen (PCNA)-immunohistochemistry was used for demonstrating the spatiotemporal course of proliferation in the brains of embryonic (24 h) through postembryonic (5 days) zebrafish (Danio rerio). Pa rallel series of the same stages prepared according to the combined Bodian fiber silver-stain/cresyl Nissl-stain were used for improved morphogenetic analysis (i.e., in detecting critical neuroanatomical landmarks). Starting from an essentially ubiquituous proliferation throughout the neural tube be fore 24 h, PCNA-immunoreactive cells become successively more restricted to a subset of gray matter cells around 48 h and even more distinct prolifera tion zones become apparent around 72 h. Both hindbrain and forebrain reveal a segmental organization with regard to the distribution of proliferation zones, but the rhombomeric pattern of PCNA-immunoreactive cells emerging be tween 48 h and 72 h precedes a similar prosomeric pattern by about 48 h. Tw o divisions of the midbrain-hindbrain boundary are described here morpholog ically and both are demonstrated to show sustained proliferation throughout the investigated time frame. In contrast, proliferation in the adjacent me sencephalic and cerebellar domains is rapidly down-regulated during the fir st 5 days of development.