Radial Columnar Patches in the Chimeric Cerebral Cortex Visualized by Use of Mouse Embryonic Stem Cells Expressing β‐Galactosidase: mouse chimera/ES cell/cerebral cortex/β‐galactosidase

Presumed radial migration of neuroblasts from the ventricular to pial surface during formation of the cerebral cortex predicts radial columnar patches in chimeric brains. Lack of adequate cell marker for neurons, however, has hindered such chimera analysis. We used a mouse embryonic stem cell line expressing β‐galactosidase gene to produce chimeric brains. Patches of the labeled cells were examined by whole mount staining and also by computer‐assisted three‐dimensional reconstruction from serial paraffin sections. Our study revealed presence of coherent radial columnar patches in the prenatal cerebral cortex, thus giving a direct evidence for the radial migration of neurons. These columnar patches were less clear in adult brains, suggesting cell mixing during later development and maturation.