Figure 4.
Regional specification of NSCs in the embryo and the adult brain. The left two panels show cross sections of the mouse forebrain from embryonic and adult brain showing four subdivisions of the VZ in different colors. On the right, RG in embryonic development (lower four panels) and type B cells in the adult brain (upper four panels) from the major forebrain subregions (septum, cortex, LGE, and MGE) are illustrated using the same colors as on the left. NSCs in the different subregions generate different types of neurons. Combinations of transcription factor expression (see text for additional details) define the different subdomains and the types of neurons produced. Representative camera lucida drawings of neuronal types produced within each subregion are illustrated. For example, neurons derived from cortical (green) RG in development give rise to large pyramidal neurons. In the adult, cortical progenitors give rise to olfactory bulb interneurons. NSCs in each subregion may give rise to an even wider diversity of cell types. Although in some cases (e.g., embryonic cortex) neuron progeny migrate radially, more frequently, immature neurons migrate tangentially for some distance before differentiating. Therefore, although mature neurons are shown deriving from distinct proliferative regions, we do not denote ultimate location, but rather that different neuronal phenotypes are derived from distinct pools of NSCs. LGE, lateral ganglionic eminence; MGE, medial ganglionic eminence; NSCs, neural stem cells; RG, radial glia; VZ, ventricular zone.