Neural Stem Cell Regulation by Adhesion Molecules Within the Subependymal Niche
In the mammalian adult brain, neural stem cells persist in neurogenic niches. The subependymal zone is the most prolific neurogenic niche in adult rodents, where residing stem cells generate large numbers of immature neurons that migrate into the olfactory bulb, where they differentiate into different types of interneurons. Subependymal neural stem cells derive from embryonic radial glia and retain some of their features like apico-basal polarity, with apical processes piercing the ependymal layer, and a basal process contacting blood vessels, constituting an epithelial niche. Conservation of the cytoarchitecture of the niche is of crucial importance for the maintenance of stem cells and fo…
Stable and Efficient Genetic Modification of Cells in the Adult Mouse V-SVZ for the Analysis of Neural Stem Cell Autonomous and Non-autonomous Effects
Relatively quiescent somatic stem cells support life-long cell renewal in most adult tissues. Neural stem cells in the adult mammalian brain are restricted to two specific neurogenic niches: the subgranular zone of the dentate gyrus in the hippocampus and the ventricular-subventricular zone (V-SVZ; also called subependymal zone or SEZ) in the walls of the lateral ventricles. The development of in vivo gene transfer strategies for adult stem cell populations (i.e. those of the mammalian brain) resulting in long-term expression of desired transgenes in the stem cells and their derived progeny is a crucial tool in current biomedical and biotechnological research. Here, a direct in vivo method …
Endothelial NT-3 Delivered by Vasculature and CSF Promotes Quiescence of Subependymal Neural Stem Cells through Nitric Oxide Induction
SummaryInteractions of adult neural stem cells (NSCs) with supportive vasculature appear critical for their maintenance and function, although the molecular details are still under investigation. Neurotrophin (NT)-3 belongs to the NT family of trophic factors, best known for their effects in promoting neuronal survival. Here we show that NT-3 produced and secreted by endothelial cells of brain and choroid plexus capillaries is required for the quiescence and long-term maintenance of NSCs in the mouse subependymal niche. Uptake of NT-3 from irrigating vasculature and cerebrospinal fluid (CSF) induces the rapid phosphorylation of endothelial nitric oxide (NO) synthase present in the NSCs, lea…
Cyclin-dependent kinase inhibitor p21 controls adult neural stem cell expansion by regulating Sox2 gene expression.
Summary In the adult brain, continual neurogenesis of olfactory neurons is sustained by the existence of neural stem cells (NSCs) in the subependymal niche. Elimination of the cyclin-dependent kinase inhibitor 1A (p21) leads to premature exhaustion of the subependymal NSC pool, suggesting a relationship between cell cycle control and long-term self-renewal, but the molecular mechanisms underlying NSC maintenance by p21 remain unexplored. Here we identify a function of p21 in the direct regulation of the expression of pluripotency factor Sox2, a key regulator of the specification and maintenance of neural progenitors. We observe that p21 directly binds a Sox2 enhancer and negatively regulate…
Transcriptional repression of Bmp2 by p21(Waf1/Cip1) links quiescence to neural stem cell maintenance.
Relative quiescence and self renewal are defining features of adult stem cells, but their potential coordination remains unclear. Subependymal neural stem cells (NSCs) lacking cyclin-dependent kinase (CDK) inhibitor (CKI) 1a (p21) exhibit rapid expansion that is followed by their permanent loss later in life. Here we demonstrate that transcription of the gene encoding bone morphogenetic protein 2 (Bmp2) in NSCs is under the direct negative control of p21 through actions that are independent of CDK. Loss of p21 in NSCs results in increased levels of secreted BMP2, which induce premature terminal differentiation of multipotent NSCs into mature non-neurogenic astrocytes in an autocrine and/or …
Regulated segregation of kinase Dyrk1A during asymmetric neural stem cell division is critical for EGFR-mediated biased signaling.
SummaryStem cell division can result in two sibling cells exhibiting differential mitogenic and self-renewing potential. Here, we present evidence that the dual-specificity kinase Dyrk1A is part of a molecular pathway involved in the regulation of biased epidermal growth factor receptor (EGFR) signaling in the progeny of dividing neural stem cells (NSC) of the adult subependymal zone (SEZ). We show that EGFR asymmetry requires regulated sorting and that a normal Dyrk1a dosage is required to sustain EGFR in the two daughters of a symmetrically dividing progenitor. Dyrk1A is symmetrically or asymmetrically distributed during mitosis, and biochemical analyses indicate that it prevents endocyto…
The APC/C cofactor Cdh1 prevents replicative stress and p53-dependent cell death in neural progenitors
The E3-ubiquitin ligase APC/C-Cdh1 is essential for endoreduplication but its relevance in the mammalian mitotic cell cycle is still unclear. Here we show that genetic ablation of Cdh1 in the developing nervous system results in hypoplastic brain and hydrocephalus. These defects correlate with enhanced levels of Cdh1 substrates and increased entry into the S phase in neural progenitors. However, cell division is prevented in the absence of Cdh1 due to hyperactivation of cyclin-dependent kinases, replicative stress, induction of p53, G2 arrest and apoptotic death of these progenitor cells. Concomitant ablation of p53 rescues apoptosis but not replicative stress, resulting in the presence of …
MT5-MMP regulates adult neural stem cell functional quiescence through the cleavage of N-cadherin.
The identification of mechanisms that maintain stem cell niche architecture and homeostasis is fundamental to our understanding of tissue renewal and repair. Cell adhesion is a well-characterized mechanism for developmental morphogenetic processes, but its contribution to the dynamic regulation of adult mammalian stem cell niches is still poorly defined. We show that N-cadherin-mediated anchorage of neural stem cells (NSCs) to ependymocytes in the adult murine subependymal zone modulates their quiescence. We further identify MT5-MMP as a membrane-type metalloproteinase responsible for the shedding of the N-cadherin ectodomain in this niche. MT5-MMP is co-expressed with N-cadherin in adult N…
Paracrine regulation of neural stem cells in the subependymal zone.
Stem cells maintain their self-renewal and multipotency capacities through a self-organizing network of transcription factors and intracellular pathways activated by extracellular signaling from the microenvironment or "niche" in which they reside in vivo. In the adult mammalian brain new neurons continue to be generated throughout life of the organisms and this lifelong process of neurogenesis is supported by a reservoir of neural stem cells in the germinal regions. The discovery of adult neurogenesis in the mammalian brain has sparked great interest in defining the conditions that guide neural stem cell (NSC) maintenance and differentiation into the great variety of neuronal and glial sub…
The rates of adult neurogenesis and oligodendrogenesis are linked to cell cycle regulation through p27-dependent gene repression of SOX2
Abstract Cell differentiation involves profound changes in global gene expression that often have to occur in coordination with cell cycle exit. Because cyclin-dependent kinase inhibitor p27 reportedly regulates proliferation of neural progenitor cells in the subependymal neurogenic niche of the adult mouse brain, but can also have effects on gene expression, we decided to molecularly analyze its role in adult neurogenesis and oligodendrogenesis. At the cell level, we show that p27 restricts residual cyclin-dependent kinase activity after mitogen withdrawal to antagonize cycling, but it is not essential for cell cycle exit. By integrating genome-wide gene expression and chromatin accessibil…