SummaryThe identification of neural stem cells (NSCs) in situ has been prevented by the inability to identify a marker consistently expressed in all adult NSCs and is thus generally accomplished using the in vitro neurosphere-forming assay. The high-mobility group transcription factor Sox2 is expressed in embryonic neural epithelial stem cells; because these cells are thought to give rise to the adult NSC population, we hypothesized that Sox2 may continue to be expressed in adult NSCs. Using Sox2:EGFP transgenic mice, we show that Sox2 is expressed in neurogenic regions along the rostral-caudal axis of the central nervous system throughout life. Furthermore, all neurospheres derived from these neurogenic regions express Sox2, suggesting that Sox2 is indeed expressed in adult NSCs. We demonstrate that NSCs are heterogeneous within the adult brain, with differing capacities for cell production. In vitro , all neurospheres express Sox2, but the expression of markers common to early progenitor cells within individual neurospheres varies; this heterogeneity of NSCs is mirrored in vivo . For example, both glial fibrillary acidic protein and NG2 are expressed within individual neurospheres, but their expression is mutually exclusive; likewise, these two markers show distinct staining patterns within the Sox2+ regions of the brain's neurogenic regions. Thus, we propose that the expression of Sox2 is a unifying characteristic of NSCs in the adult brain, but that not all NSCs maintain the ability to form all neural cell types in vivo .

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ABSTRACTand was abolished by mitochondrial depolarization. The secondary increase was associated with spreading of the dye from punctate staining to whole-cell distribution, and was delayed significantly by the MTP inhibitor cyclosporin A and the smooth endoplasmic reticulum Ca 2ϩ ATPase inhibitor thapsigargin. We conclude that MeHg causes release of Ca 2ϩ from the mitochondria through opening of the MTP, which contributes the bulk of the elevated [Ca 2ϩ ] i observed during MeHg neurotoxicity. Additionally, the Ca 2ϩ that enters the mitochondria seems to originate in the smooth endoplasmic reticulum, providing a mechanism for the observed mitochondrial Ca 2ϩ overload.