Neural stem cells generate a wide spectrum of cell types in developing and adult nervous systems. These cells are marked by expression of the intermediate filament nestin. We used the regulatory elements of the nestin gene to generate transgenic mice in which neural stem cells of the embryonic and adult brain are marked by the expression of green fluorescent protein (GFP). We used these animals as a reporter line for studying neural stem and progenitor cells in the developing and adult nervous systems. In these nestin-GFP animals, we found that GFP-positive cells reflect the distribution of nestin-positive cells and accurately mark the neurogenic areas of the adult brain. Nestin-GFP cells can be isolated with high purity by using fluorescent-activated cell sorting and can generate multipotential neurospheres. In the adult brain, nestin-GFP cells are ϳ1,400-fold more efficient in generating neurospheres than are GFP-negative cells and, despite their small number, give rise to 70 times more neurospheres than does the GFP-negative population. We characterized the expression of a panel of differentiation markers in GFP-positive cells in the nestin-GFP transgenics and found that these cells can be divided into two groups based on the strength of their GFP signal: GFP-bright cells express glial fibrillary acidic protein (GFAP) but not ␤III-tubulin, whereas GFP-dim cells express ␤III-tubulin but not GFAP. These two classes of cells represent distinct classes of neuronal precursors in the adult mammalian brain, and may reflect different stages of neuronal differentiation. We also found unusual features of nestin-GFP-positive cells in the subgranular cell layer of the dentate gyrus. Together, our results indicate that GFP-positive cells in our transgenic animals accurately represent neural stem and progenitor cells and suggest that these nestin-GFP-expressing cells encompass the majority of the neural stem cells in the adult brain.

We found that the Drosophila brain is assembled from families of multiple LPUs and their interconnections. This provides an essential first step in the analysis of information processing within and between neurons in a complete brain.

Accumulation of amyloid-␤ (A␤) peptides in the brain has been suggested to be the primary event in sequential progression of Alzheimer's disease (AD). Here, we use Drosophila to examine whether expression of either the human A␤40 or A␤42 peptide in the Drosophila brain can induce pathological phenotypes resembling AD. The expression of A␤42 led to the formation of diffused amyloid deposits, age-dependent learning defects, and extensive neurodegeneration. In contrast, expression of A␤40 caused only age-dependent learning defects but did not lead to the formation of amyloid deposits or neurodegeneration. These results strongly suggest that accumulation of A␤42 in the brain is sufficient to cause behavioral deficits and neurodegeneration. Moreover, Drosophila may serve as a model for facilitating the understanding of molecular mechanisms underlying A␤ toxicity and the discovery of novel therapeutic targets for AD. A lzheimer's disease (AD) is a neurodegenerative disorder characterized clinically by progressive decline in memory accompanied by histological changes, including neuronal loss and the formation of neurofibrillary tangles (NFTs) and senile plaques (1). The accumulation of amyloid-␤ (A␤)42 peptide, the major component of senile plaques, has been hypothesized to be the primary event in AD pathogenesis (2, 3). The strongest support for the A␤ hypothesis comes from genetic analyses of familial AD (FAD); most FAD mutations identified in A␤ precursor protein (APP), Presenilin1 (PS1) and Presenilin2 (PS2) genes appear to cause excessive accumulation of A␤42 (4). Secretion of A␤ peptides is a result of sequential cleavage of APP by ␤-secretase, a type I transmembrane glycosylated aspartyl protease, and ␥-secretase, a large protein complex that includes at least four proteins, Presenilins (PS1 or PS2), Nicastrin, Aph-1, and Pen-2 (for review, see ref. 5). The heterogeneity of ␥-secretase cleavage gives rise to a series of A␤ peptides, including the major species A␤40 and a smaller amount of A␤42.To study AD pathogenesis in vivo, a number of AD mouse models have been established and have successfully recapitulated AD-like phenotypes, including abundant amyloid deposits, astroglial activation, synaptic loss and dysfunction, behavioral abnormalities, and neurodegeneration (6-15). In addition to these mouse models, the model systems that allow highthroughput genetic screening will facilitate the discovery of genes involved in AD pathogenesis. Furthermore, one of the intriguing issues that have not been elucidated in these transgenic mice is the pathological roles of each specific A␤ species (i.e., A␤40 and A␤42), because currently available mouse models mainly rely on overexpression of APP.We use a Drosophila model (16) to compare the specific pathological roles of A␤40 and A␤42. In Drosophila, all components involved in the protein complex responsible for ␥-secretase activity are highly conserved (17), whereas ␤-secretase activity is absent or very low (18). An APP-like protein (APPL) is also present in flies, althou...