CXCR4 prevents dispersion of granule neuron precursors in the adult dentate gyrus

Neurogenesis in the adult dentate gyrus (DG) generates new granule neurons that differentiate in the inner one‐third of the granule cell layer (GCL). The migrating precursors of these neurons arise from neural stem cells (NSCs) in the subgranular zone (SGZ). Although it is established that pathological conditions, including epilepsy and stroke, cause dispersion of granule neuron precursors, little is known about the factors that regulate their normal placement. Based on the high expression of the chemokine CXCL12 in the adult GCL and its role in guiding neuronal migration in development, we addressed the function of the CXCL12 receptor CXCR4 in adult neurogenesis. Using transgenic reporter mice, we detected Cxcr4‐GFP expression in NSCs, neuronal‐committed progenitors, and immature neurons of adult and aged mice. Analyses of hippocampal NSC cultures and hippocampal tissue by immunoblot and immunohistochemistry provided evidence for CXCL12‐promoted phosphorylation/activation of CXCR4 receptors in NSCs in vivo and in vitro. Cxcr4 deletion in NSCs of the postnatal or mature DG using Cre technology reduced neurogenesis. Fifty days after Cxcr4 ablation in the mature DG, the SGZ showed a severe reduction of Sox2‐positive neural stem/early progenitor cells, NeuroD‐positive neuronal‐committed progenitors, and DCX‐positive immature neurons. Many immature neurons were ectopically placed in the hilus and inner molecular layer, and some developed an aberrant dendritic morphology. Only few misplaced cells survived permanently as ectopic neurons. Thus, CXCR4 signaling maintains the NSC pool in the DG and specifies the inner one‐third of the GCL as differentiation area for immature granule neurons. © 2013 Wiley Periodicals, Inc.     

Interactions between human adipose stromal cells and mouse neural stem cells in vitro

Transplantation of adult mesenchymal stem cells (MSCs) into adult rat brain has been known to reduce functional deficits associated with stroke and traumatic brain injury. However, in injured brains, there is no evidence that transplanted MSCs replace lost host brain tissue. In this study, we determined in vitro interaction between human adipose tissue stromal cells (hATSCs), a kind of MSC, and neural stem cells (NSCs). hATSCs were isolated and proliferated from human adipose tissues, and NSCs from the subventricular zone of postnatal mice. When NSCs were cultured on mitomycin-treated hATSC monolayers, their proliferation was decreased, but neuronal differentiation was significantly induced. The percentage of neurons significantly increased in 7 days in cultures of NSCs on hATSCs feeder as compared to NSCs cultured on laminin-coated dishes. When the duration of the cultures was extended to 14 days, hATSCs supported the survival of neurons derived from NSCs. To determine the role of soluble factors from hATSCs, NSCs were cultured with hATSCs conditioned medium or co-cultured with permeable filter on which hATSCs were grown. Although proliferation of NSCs significantly decreased and glial differentiation increased under these experimental conditions, their neuronal differentiation was not affected, indicating that direct physical contact between hATSCs and NSCs is required for induction of neuronal differentiation. These data indicate that hATSCs may provide supportive roles on endogenous neural stem cells, when they are transplanted into damaged brain.     

Adult neurogenesis and gliogenesis in the dorsal and ventral canine hippocampus

Dentate gyrus (DG) of the mammalian hippocampus gives rise to new neurons and astrocytes all through adulthood. Canine hippocampus presents many similarities in fetal development, anatomy, and physiology with human hippocampus, establishing canines as excellent animal models for the study of adult neurogenesis. In the present study, BrdU-dated cells of the structurally and functionally dissociated dorsal (dDG) and ventral (vDG) adult canine DG were comparatively examined over a period of 30 days. Each part's neurogenic potential, radial glia-like neural stem cells (NSCs) proliferation and differentiation, migration, and maturation of their progenies were evaluated at 2, 5, 14, and 30 days post BrdU administration, with the use of selected markers (glial fibrillary acidic protein, doublecortin, calretinin and calbindin). Co-staining of BrdU+ cells with NeuN or S100B permitted the parallel study of the ongoing neurogenesis and gliogenesis. Our findings reveal the comparatively higher populations of residing granule cells, proliferating NSCs and BrdU+ neurons in the dDG, whereas newborn neurons of the vDG showed a prolonged differentiation, migration, and maturation. Newborn astrocytes were found all along the dorso-ventral axis, counting however for only 11% of newborn cell population. Comparative evaluation of adult canine and rat neurogenesis revealed significant differences in the distribution of resident and newborn granule cells along the dorso-ventral axis, division pattern of adult NSCs, maturation time plan of newborn neurons, and ongoing gliogenesis. Concluding, spatial and temporal features of adult canine neurogenesis are similar to that of other gyrencephalic species, including humans, and justify the comparative examination of adult neurogenesis across mammalian species.     

Neurogenesis in Talpha-1 tubulin transgenic mice during development and after injury

Talpha-1 tubulin promoter-driven EYFP expression is seen in murine neurons born as early as E9.5. Double labeling with markers for stem cells (Sox 1, Sox 2, nestin), glial progenitors (S100beta, NG2, Olig2), and neuronal progenitors (doublecortin, betaIII-tubulin, PSA-NCAM) show that Talpha-1 tubulin expression is limited to early born neurons. BrdU uptake and double labeling with neuronal progenitor markers in vivo and in vitro show that EYFP-expressing cells are postmitotic and Talpha-1 tubulin EYFP precedes the expression of MAP-2 and NeuN, and follows the expression of PSA-NCAM, doublecortin (Dcx), and betaIII-tubulin. Talpha-1 tubulin promoter-driven EYFP expression is transient and disappears in most neurons by P0. Persistent EYFP expression is mainly limited to scattered cells in the subventricular zone (SVZ), rostral migratory stream, and hippocampus. However, there are some areas that continue to express Talpha-1 tubulin in the adult without apparent neurogenesis. The number of EYFP-expressing cells declines with age indicating that Talpha-1 tubulin accurately identifies early born postmitotic neurons throughout development but less clearly in the adult. Assessment of neurogenesis after stab wound injuries in the cortex, cerebellum and spinal cord of adult animals shows no neurogenesis in most areas with an increase in BrdU incorporation in glial and other non neuronal populations. An up-regulation of Talpha-1 tubulin can be seen in certain areas unaccompanied by new neurogenesis. Our results suggest that even if stem cells proliferate their ability to generate neurons is limited and caution is warranted in attributing increased BrdU incorporation to stem cells or cells fated to be neurons even in neurogenic areas.     

神经干细胞分化为神经元的基因调控

神经干细胞的研究进展为神经退行性病变和神经系统损伤的功能重建带来了令人振奋的希望。促使神经干细胞定向分化成所需神经元是实现神经干细胞临床应用的重要关键。目前对神经干细胞分化的分子机制还没有完全阐明。神经干细胞的分化与一系列因素促进转录因子表达有关,这些因子启动中枢神经系统基因表达程序从而导致神经干细胞向不同谱系分化。本文对神经干细胞分化为神经元过程中的基因调控的最新研究进展作一综述。