Neural stem cells critically regulate brain morphogenesis and nervous system adaptation to neuropathological insults. They are the likely cells of origin for both childhood and adult brain tumors and represent a potentially rich source of transplantable cells for treatment of a wide range of human neurological diseases. Neural stem cells can be isolated and expanded from both embryonic and adult brain or be derived from embryonic stem (ES) cells. Recent studies have demonstrated a critical requirement for DNA repair enzymes and telomerase in early brain development and an unexpectedly high frequency of chromosomal abnormalities and apoptosis in neural stem cells. Because of the tremendous biological significance of neural stem cells and the cell specificity of apoptotic death pathways, we have performed a series of studies on the molecular regulation of DNA damage-induced neural stem cell apoptosis. Our initial investigations, using mice with targeted gene disruptions and in vivo and in vitro models of neural stem cell death, have revealed an apoptotic pathway involving p53, pro-apoptotic multi-domain Bcl-2 family members, Apaf-1, and caspase-9. Neural stem cell death requires new gene transcription and protein translation, but surprisingly, not caspase-3 activation. This apoptotic pathway is recapitulated in fibroblastic growth factor (FGF)-2 expanded neural stem cells and may involve Noxa, a BH3 domain-only Bcl-2 family member. We hypothesize that irreparable DNA damage to neural stem cells triggers p53-dependent upregulation of Noxa which promotes Bax/Bak mediated cytochrome c release, caspase-9 activation and death. To test this hypothesis, we will use FGF-2 expanded telencephalic neural stem cells derived from wild-type and gene disrupted mice, gene transfections, and antisense oligonucleotide modification of mRNA expression levels. We will determine if Noxa expression is necessary and sufficient for p53-dependent neural stem cell death and the caspase family requirements for DNA damage-induced neural stem cell apoptosis. These studies will define the key molecules regulating death in this important cell population and provide new insights into neural stem cell biology.
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