Stem cells reside in specialized niches that regulate their self-renewal and differentiation. The vasculature is emerging as an important component of stem cell niches. Here, we show that the adult subventricular zone (SVZ) neural stem cell niche contains an extensive planar vascular plexus that has specialized properties. Dividing stem cells and their transit-amplifying progeny are tightly apposed to SVZ blood vessels both during homeostasis and regeneration. They frequently contact the vasculature at sites that lack astrocyte endfeet and pericyte coverage, a modification of the blood-brain barrier unique to the SVZ. Moreover, regeneration often occurs at these sites. Finally, we find that circulating small molecules in the blood enter the SVZ. Thus, the vasculature is a key component of the adult SVZ neural stem cell niche, with SVZ stem cells and transit-amplifying cells uniquely poised to receive spatial cues and regulatory signals from diverse elements of the vascular system.

The subventricular zone (SVZ) is the largest neurogenic niche in the adult mammalian brain. Here we show that the brain-enriched microRNA miR-124 is an important regulator of the temporal progression of adult neurogenesis in mice. Knockdown of endogenous miR-124 maintains purified SVZ stem cells as dividing precursors, whereas ectopic expression leads to precocious and increased neuron formation. Furthermore, blocking miR-124 function during regeneration leads to hyperplasias followed by a delayed burst of neurogenesis. We identify the SRY-box transcription factor Sox9 to be a physiological target of miR-124 at the transition from transit amplifying cell to neuroblast stage. Sox9 over-expression abolishes neuronal differentiation whereas Sox9 knockdown leads to increased neuron formation. Thus, miR-124 mediated repression of Sox9 is important for progression along the SVZ stem cell lineage to neurons.

Chemical synapses are complex structures that mediate rapid intercellular signalling in the nervous system. Proteomic studies suggest that several hundred proteins will be found at synaptic specializations. Here we describe a systematic screen to identify genes required for the function or development of Caenorhabditis elegans neuromuscular junctions. A total of 185 genes were identified in an RNA interference screen for decreased acetylcholine secretion; 132 of these genes had not previously been implicated in synaptic transmission. Functional profiles for these genes were determined by comparing secretion defects observed after RNA interference under a variety of conditions. Hierarchical clustering identified groups of functionally related genes, including those involved in the synaptic vesicle cycle, neuropeptide signalling and responsiveness to phorbol esters. Twenty-four genes encoded proteins that were localized to presynaptic specializations. Loss-of-function mutations in 12 genes caused defects in presynaptic structure.