In the developing central nervous system (CNS), Notch signaling preserves 
progenitor pools and inhibits neurogenesis and oligodendroglial differentiation. 
It has recently been postulated that Notch instructively drives astrocyte 
differentiation. Whether the role of Notch signaling in promoting astroglial 
differentiation is permissive or instructive has been debated. We report here 
that the astrogliogenic role of Notch is in part mediated by direct binding of 
the Notch intracellular domain to the CSL DNA binding protein, forming a 
transcriptional activation complex onto the astrocyte marker gene, glial 
fibrillary acidic protein (GFAP). In addition, we found that, in CSL-/- neural 
stem cell cultures, astrocyte differentiation was delayed but continued at a 
normal rate once initiated, suggesting that CSL is involved in regulating the 
onset of astrogliogenesis. Importantly, although the classical CSL-dependent 
Notch signaling pathway is intact and able to activate the Notch canonical 
target promoter during the neurogenic phase, it is unable to activate the GFAP 
promoter during neurogenesis. Therefore, the effect of Notch signaling on target 
genes is influenced by cellular context in regulation of neurogenesis and 
gliogenesis.