Allocation of mouse cerebellar granule cells derived from embryonic ventricular progenitors--a study using a recombinant retrovirus.

Granule cells of the mammalian cerebellar cortex originate from embryonic progenitors present in the ventricular germinal layer. To investigate the allocation fate of these ventricular progenitors in the mouse, we labeled a few of them on embryonic day 13 with a recombinant retrovirus carrying lacZ which encodes E. coli beta-galactosidase (beta-gal), and the labeled cells in the postnatal cerebellar cortex were detected by beta-gal histochemistry. In the postnatal cerebellar cortex, the virally-labeled beta-gal+ granule cells formed discrete clusters. These clusters were not compactly packed with the beta-gal+ cells, and there was intermingling with beta-gal- granule cells. Neither beta-gal+ Purkinje cells nor glia were found to be included in the clusters. Most of the granule cell clusters were incompatible with the functional areas of the cortex. These results suggest: (1) granule cells derived from individual ventricular progenitors are allocated in clusters and are not extensively dispersed, (2) granule cells descended from one progenitor may mix with their neighbors that are descended from another progenitor, (3) the allocation fate of the ventricular progenitors of granule cells is not restricted to the functional areas of the cerebellar cortex.