Identification of a transient subpial neurogenic zone in the developing dentate gyrus and its regulation by Cxcl12 and reelin signaling.
ABSTRACT One striking feature of dentate gyrus development, distinct from the other cortical structures, is the relocation of neural precursors from the ventricular zone to the forming dentate pole to produce a lifelong neurogenic subgranular zone (SGZ). In this study, we demonstrate that dentate progenitors first dwell for up to 1 week in a previously unrecognized neurogenic zone intimately associated with the pial meningeal surface lining the outer edge of the forming dentate. This zone also serves as the organizational matrix for the initial formation of the dentate glial scaffolding. Timely clearance of neural precursors from their transient location depends on reelin, whereas initial formation of this transient stem cell niche requires Cxcl12-Cxcr4 signaling. The final settlement of the neural precursors at the subgranular zone relies on a pertussis toxin-sensitive pathway independent of Cxcl12-Cxcr4 signaling. Furthermore, genetic fate-mapping analysis suggests that subpial precursors contribute to the SGZ formation. These results demonstrate that the relocation of neural precursors in the dentate gyrus consists of discrete steps regulated by multiple pathways.
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ABSTRACT: Neurogenesis persists in adult mammals in specific brain areas, known as neurogenic niches. Adult neurogenesis is highly dynamic and is modulated by multiple physiological stimuli and pathological states. There is a strong interest in understanding how this process is regulated, particularly since active neuronal production has been demonstrated in both the hippocampus and the subventricular zone (SVZ) of adult humans. The molecular mechanisms that control neurogenesis have been extensively studied during embryonic development. Therefore, we have a broad knowledge of the intrinsic factors and extracellular signaling pathways driving proliferation and differentiation of embryonic neural precursors. Many of these factors also play important roles during adult neurogenesis, but essential differences exist in the biological responses of neural precursors in the embryonic and adult contexts. Because adult neural stem cells (NSCs) are normally found in a quiescent state, regulatory pathways can affect adult neurogenesis in ways that have no clear counterpart during embryogenesis. BMP signaling, for instance, regulates NSC behavior both during embryonic and adult neurogenesis. However, this pathway maintains stem cell proliferation in the embryo, while it promotes quiescence to prevent stem cell exhaustion in the adult brain. In this review, we will compare and contrast the functions of transcription factors (TFs) and other regulatory molecules in the embryonic brain and in adult neurogenic regions of the adult brain in the mouse, with a special focus on the hippocampal niche and on the regulation of the balance between quiescence and activation of adult NSCs in this region.Frontiers in Cellular Neuroscience 11/2014; 8:396. DOI:10.3389/fncel.2014.00396 · 4.18 Impact Factor
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ABSTRACT: Recent evidence implicates adult hippocampal neurogenesis in regulating behavioral and physiologic responses to stress. Hippocampal neurogenesis occurs across the lifespan, however the rate of cell birth is up to 300% higher in adolescent mice compared to adults. Adolescence is a sensitive period in development where emotional circuitry and stress reactivity undergo plasticity establishing life-long set points. Therefore neurogenesis occurring during adolescence may be particularly important for emotional behavior. However, little is known about the function of hippocampal neurons born during adolescence. In order to assess the contribution of neurons born in adolescence to the adult stress response and depression-related behavior, we transiently reduced cell proliferation either during adolescence, or during adulthood in GFAP-Tk mice. We found that the intervention in adolescence did not change adult baseline behavioral response in the forced swim test, sucrose preference test or social affiliation test, and did not change adult corticosterone responses to an acute stressor. However following chronic social defeat, adult mice with reduced adolescent neurogenesis showed a resilient phenotype. A similar transient reduction in adult neurogenesis did not affect depression-like behaviors or stress induced corticosterone. Our study demonstrates that hippocampal neurons born during adolescence, but not in adulthood are important to confer susceptibility to chronic social defeat.Frontiers in Behavioral Neuroscience 08/2014; 8:289. DOI:10.3389/fnbeh.2014.00289 · 4.16 Impact Factor
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ABSTRACT: Adverse early life experience decreases adult hippocampal neurogenesis and results in increased vulnerability to neuropsychiatric disorders. Despite that the effects of postnatal stress on neurogenesis have been widely studied in adult individuals, few efforts have been done to evaluate its immediate effects on the developing hippocampus. Moreover, it is not clear whether postnatal stress causes a differential impact in hippocampus development in male and female neonates that could be related to emotional deficits in adulthood. It has been proposed that the long term effects of early stress exposure rise from a persistent HPA axis activation during sensitive time windows; nevertheless the exact mechanisms and mediators remain unknown. Here, we summarize the immediate and late effects of early life stress on hippocampal neurogenesis in male and female rat pups, compare its later consequences in emotionality, and highlight some relevant mediator peptides that could be potentially involved in programming.Frontiers in Molecular Neuroscience 02/2015; 8:3. DOI:10.3389/fnmol.2015.00003