Fig. 9.

Schematic representation of cells expressing m-Msi-1 during embryonic and postnatal CNS development. Solid patterns represent m-Msi-1-positive cells. In the embryonic CNS, m-Msi-1 is expressed in proliferating neural precursors in the ventricular zone (VZ); these cells are capable of self-renewal and generate postmitotic neurons, as described previously (Sakakibara et al., 1996). In the perinatal stage, the VZ shrinks and a second proliferative SVZ appears. Postnatally, m-Msi-1 expression is seen in proliferating glial precursors in the SVZ and cells of astrocyte lineage, including ependymal cells and Bergmann glia. At present, it is not known whether neural precursors in the embryonic VZ generate glial precursors in the postnatal SVZ, or whether bipotent glial precursors in the postnatal SVZ generate the astrocyte and O-2A-oligodendrocyte lineages through an “asymmetric cell division.” However, this asymmetric division at least may occur when neuronal precursors give rise to neurons in the embryonic VZ (Chenn and McConnell, 1995). The expression of m-Msi-1 in some populations of neurons is not represented for reasons of simplicity.