In the early embryonic stage, mouse neural epithelial cells divide to expand the neural-epithelial-cell pool. After the cell division, one of the neural epithelial cells inherits the basal process, and the other epithelial cell generates a new basal process. In the following stage, the neural epithelial cells become nestin-positive and behave as neurogenic progenitors. Moreover, most researchers have been believing that the neurogenic epithelial cells (radial glia) maintain basal processes (radial fiber) and bud neuron precursors which migrate radially along the radial fibers, while some of them inherit radial fiber as outer radial glia. However, those researchers investigate the radial glia division by labeling both of the daughter cells with GFP fluorescence, which does not reveal how the two daughter cells and processes are connected clearly.
Here, we investigated how the radial glia divide in the NeuroD6-Cre knock-in mouse embryos by transducing the radial glia with recombinant adenovirus carrying floxed mRFP-cDNA plus GFP cDNA. As the result, mRFP-positive radial glia divided and produced mRFP-positive spherical cells and GFP labeled outer radial glia-like cells. It means that all the radial fibers are inherited by neuron precursors. Moreover, the radial glia became spherical cell and renewed the radial fiber. The radial glia division style is also confirmed by electron microscopic analysis. Therefore, as the neocortex become thicker, it takes longer to renew the radial fiber contacting the basal lamina and to enter next cell cycle.
Here, we conclude that both neural epithelial cells and radial glia divide in the same style. All neuron precursors appear as outer radial glia-like cells. Then they lose radial fibers and turn into multipolar cells.