Overview of the cerebellar architecture in zebrafish. (A) In the adult zebrafish brain neural stem cells are abundant and distributed in distinct topological clusters along the whole rostro-caudal brain axis; (B)
A schematic coronal section showing the anatomy of the zebrafish cerebellum. The cerebellum has a simple laminar three layered architecture consisting of a molecular layer (ML), Purkinje cell layer (PL) and a granule cell layer (GL). The granule layer consists of excitatory granule cells and inhibitory Golgi neurons. The Purkinje cell layer contains Purkinje neurons (PN), Bergmann glia (G), and excitatory eurydendroid cells (E). The ML mainly consists of nerve fibers and scattered inhibitory stellate cells. Boxed region. Neural progenitors are maintained in the dorsomedial part of the cerebellum around a remnant of the IVth ventricle (the cerebellar recessus, CR). The progenitors give rise to granule neurons in a distinct outside-in fashion. (1) Polarized neuroepithelial-like progenitors (green) are restricted to the midline of the dorsal cerebellum. The progenitors give rise to rapidly migrating granule precursors (dark green) that initially migrate dorsolaterally. After reaching the meninge the granule precursors migrate in ventrolateral direction to the GL. (2) Radial glia (light blue) are found close to the midline and they are used as scaffolds during the initial dorsal migration of granule precursors. C) Schematic view of the cerebellar progenitor domains during development. The cerebellar cell types are generated from two germinal zones: the ventricular zone (VZ, orange) and the upper rhombic lip (URL, green). The excitatory neurons are generated from the URL, while inhibitory neurons and glia are generated from the VZ. The cerebellar cell types are produced in a strict temporal order from increasingly committed progenitors. Purkinje neurons and deep cerebellar nuclei neurons are produced early during development, while inhibitory interneurons, granule cells and glia are produced late.