[Cortical histogenesis captured by slice culture].

Studying the mechanism of brain formation is important for the understanding of physiological and pathological conditions of the human brain and also for development of regenerative medicine. Slice culture methods coupled with sporadic labeling of cells with fluorescent materials are useful to directly observe dynamic behaviors of cells in the brain primordium. In the developing mouse neocortex, "radial glial cells" which had been thought to be non-neuronogenic are now regarded as a main progenitor population for neuron production, revitalizing Setsuya Fujita's "matrix cell theory" (J Comp Neurol, 120: 37-42, 1963). During mitosis at the ventricular surface, each progenitor cell maintains its process extended to the pial surface, giving the pial process to one of its daughter cells. Process-inheriting daughter cells, including neurons, utilize the inherited pial processes for their migration. The other histogenetic strategy that the developing neocortex employs for efficient segregation of neurons from the progenitor cells' territory is the use of the non-surface mitoses (divisions away from the ventricular surface). The non-surface-dividing progenitor cells born at the ventricular surface subsequently lose their ventricular attachment and then divide at a non-surface position, giving rise to pairs of neurons just beneath a layer into which young neurons should be inserted.