The generation of new neurons from neural stem cells is restricted to two regions of the adult mammalian central nervous system: the subventricular zone of the lateral ventricle, and the subgranular zone of the hippocampal dentate gyrus. In both regions, signals provided by the microenvironment regulate the maintenance, proliferation and neuronal fate commitment of the local stem cell population. The identity of these signals is largely unknown. Here we show that adult hippocampal stem/progenitor cells (AHPs) express receptors and signalling components for Wnt proteins, which are key regulators of neural stem cell behaviour in embryonic development. We also show that the Wnt/beta-catenin pathway is active and that Wnt3 is expressed in the hippocampal neurogenic niche. Overexpression of Wnt3 is sufficient to increase neurogenesis from AHPs in vitro and in vivo. By contrast, blockade of Wnt signalling reduces neurogenesis from AHPs in vitro and abolishes neurogenesis almost completely in vivo. Our data show that Wnt signalling is a principal regulator of adult hippocampal neurogenesis and provide evidence that Wnt proteins have a role in adult hippocampal function.

The aggregation of proteins into oligomers and amyloid fibrils is characteristic of several neurodegenerative diseases, including Parkinson disease (PD). In PD, the process of aggregation of α-synuclein (α-syn) from monomers, via oligomeric intermediates, into amyloid fibrils is considered the disease-causative toxic mechanism. We developed α-syn mutants that promote oligomer or fibril formation and tested the toxicity of these mutants by using a rat lentivirus system to investigate loss of dopaminergic neurons in the substantia nigra. The most severe dopaminergic loss in the substantia nigra is observed in animals with the α-syn variants that form oligomers (i.e., E57K and E35K), whereas the α-syn variants that form fibrils very quickly are less toxic. We show that α-syn oligomers are toxic in vivo and that α-syn oligomers might interact with and potentially disrupt membranes. P arkinson disease (PD) is the most common movement disorder, currently affecting approximately 2% of the population older than age 60 y. Prominent neuropathological hallmarks of PD are the loss of dopaminergic neurons in the substantia nigra (SN) region of the midbrain (1) and the presence of α-syn-containing intracellular inclusions: Lewy bodies (LBs) and Lewy neurites (2). α-Syn, a 140-aa protein physiologically found in presynaptic terminals of neurons, is the major fibrillar protein in LBs and Lewy neurites in sporadic and inherited PD. Moreover, point mutations (A53T, A30P, E46K) and gene multiplications of human WT (hWT) α-syn are related to rare familial autosomal-dominant forms of early-onset PD (3-6), suggesting that increased gene dosage and aberrant protein structure may accelerate disease onset and progression.Recent reports indicate that the accumulation of α-syn can result in the formation of intermediate-state oligomers, and oligomers of different shapes and sizes have been described (7-10). These oligomers interact with lipids, disrupt membranes (7,8), and cause cell death in vitro (10, 11) and in nonmammalian models, such as Caenorhabditis elegans and Drosophila melanogaster (12). However, we are aware of no previous direct in vivo demonstration of the toxicity of α-syn oligomers in mammals.We aim to establish a model that allows specific testing of the effects of α-syn oligomerization in vitro and in vivo. To elucidate the causal structure-toxicity relationship of these oligomeric protein assemblies in a mammalian system, we designed "conformation-trapped" mutants based on structural modeling of α-syn fibrils (13, 14). Structurally, amyloid fibrils of α-syn are composed of cross-β-sheets (15). Residues from approximately 30 to 110 of α-syn form the core of the fibrils, whereas the approximately 30 N-terminal residues are heterogeneous and the approximately 30 C-terminal residues are flexible (13,14,16,17). Based on our structural model, recently developed from NMR data, the core of α-syn fibrils comprises five β-strands reminiscent of a five-layered "β-sandwich" (14). Several loops adjacent to and between the strands ar...

Neural stem cells (NSCs) in the adult hippocampus divide infrequently, and the molecules that modulate their quiescence are largely unknown. Here, we show that bone morphogenetic protein (BMP) signaling is active in hippocampal NSCs, downstream of BMPR-IA. BMPs reversibly diminish proliferation of cultured NSCs while maintaining their undifferentiated state. In vivo, acute blockade of BMP signaling in the hippocampus by intracerebral infusion of Noggin first recruits quiescent NSCs into the cycle and increases neurogenesis; subsequently, it leads to decreased stem cell division and depletion of precursors and newborn neurons. Consistently, selective ablation of Bmpr1a in hippocampal NSCs, or inactivation of BMP canonical signaling in conditional Smad4 knockout mice, transiently enhances proliferation but later leads to a reduced number of precursors, thereby limiting neuronal birth. BMPs are therefore required to balance NSC quiescence/proliferation and to prevent loss of the stem cell activity that supports continuous neurogenesis in the mature hippocampus.