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Fig. 2. Maintenance of neural stem cells and promotion of astrocyte formation by
Hes genes. (A) Regulation of cell differentiation by bHLH genes.
Neuroepithelial cells initially form the neural plate. These cells gradually
develop into radial glial cells, which have a cell body in the ventricular
zone (VZ) and a radial fiber reaching the pial surface. Radial glial cells
give rise to neurons by asymmetric cell divisions. After the production of
distinct types of neurons, radial glial cells finally differentiate into
astrocytes. Hes genes maintain neuroepithelial cells and radial glial cells
during early development, and promote astrocyte formation during late
development. Proneural genes such as Mash1, Ngn2 and Math1
promote neurogenesis. Unlike other Hes genes, Hes6 also promotes
neurogenesis. The broken line indicates the border of the VZ. (B)
Transfection experiments in mouse embryonic brains. Many of the cells
transfected with a control vector that only drives enhanced green fluorescent
protein (EGFP) expression in radial glial cells have migrated out of the VZ
(at the bottom of the image) and differentiated into neurons, whereas cells
transfected with a vector that directs the co-expression of Hes1 and
EGFP, remain in the VZ and display radial glial cell morphology [from
Ohtsuka et al. (Ohtsuka et al.,
2001)]. Scale bars: 100 µm.
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