Reelin调节小鼠喙端迁移流发育的形态学观察

目的 探讨小鼠室管膜下区（SVZ）的神经干细胞孵育成熟以及沿喙端迁移流（RMS）切线迁移至嗅球(OB)的过程,尤其是Reelin对细胞迁移和细胞分化的影响。方法 选用野生型（WT）小鼠50只和纯合reeler小鼠23只胚胎16 d至生后90 d的各年龄点小鼠大脑,应用尼氏染色、免疫荧光染色、墨汁灌注及电子显微镜技术标记并观察小鼠大脑的神经干细胞、胶质细胞以及血管发生之间的相互关系,比较两组小鼠RMS的发育情况。结果 胚胎后期至出生早期,在SVZ分布着大量的胶质细胞、神经干细胞和血管网,它们相互联系构成SVZ神经干细胞孵育的血管龛(niche);神经干细胞在niche中孵育成熟后可以进入RMS,切线迁移至嗅球,到达嗅球后转变为放射状迁移,分化为各种神经元整合入嗅球;神经干细胞在RMS的迁移过程中,放射状胶质细胞协同血管为其提供支架引导;reeler小鼠也能形成RMS,但形态有所改变,主要在嗅球处,神经干细胞失去规律排列,呈散乱分布。结论 室管膜下区的niche是神经干细胞的主要来源;血管协同放射状胶质细胞为RMS中的神经干细胞提供支架引导作用;作为调节细胞迁移的重要信号,Reelin可以通过其交互作用影响血管的发育,Reelin缺失导致嗅球处神经干细胞放射状迁移的转变障碍。     

Nucleotides and epidermal growth factor induce parallel cytoskeletal rearrangements and migration in cultured adult murine neural stem cells

Aim: The adult subventricular zone (SVZ) contains neural stem cells that generate neuroblasts migrating to the olfactory bulb (OB) and differentiating into interneurones. The molecular cues controlling essential functions within the neurogenesis pathway such as proliferation, short and long distance migration, functional integration and cell survival are poorly understood. We have previously shown that cultured adult neural stem cells express a considerable variety of nucleotide receptors and that nucleotides and epidermal growth factor (EGF) induce converging intracellular signalling pathways that carry potential for synergism in the control of neural stem cell proliferation and cell survival. Here we investigate the role of EGF and the nucleotides ATP, ADPβS and UTP in neural stem cell migration. Methods: Neural stem cells were prepared from adult mice and subjected to adherent culture. Labelling of F-actin was performed with tetramethylrhodamine isothiocyanate-phalloidin. Images were processed for quantitative evaluation of fluorescence labelling. Agonist-induced phosphorylation of AKT and focal adhesion kinase was analysed by quantitative Western blotting. Agonist-dependent cell migration was assayed using 48-well microchemotaxis chambers. Results: Nucleotides and EGF induce the formation of stress fibres, an increase in the cortical actin cytoskeleton and in cell spreading. This is associated with increased phosphorylation of AKT and focal adhesion kinase. Using microchemotaxis chambers we demonstrate a parallel increase in cell migration. Conclusion: Our results suggest that nucleotides and EGF acting as paracrine or autocrine signalling substances can be of relevance for structuring and maintaining the cytoarchitecture of the SVZ and the stream of neuroblasts migrating to the OB.     

Putrescine as an important source of GABA in the postnatal rat subventricular zone

The subventricular zone (SVZ) is a neurogenic region that continually gives rise to olfactory bulb (OB) GABAergic interneurons in mammals. The newly generated neuroblasts already express GABA while migrating to this structure along the rostral migratory stream (RMS). Here, we investigate in early postnatal rat if SVZ/RMS cells undertake the same synthetic pathway by which GABA is produced in differentiated neurons, i.e. the decarboxylation of glutamate by the glutamic acid decarboxylase (GAD), or, if an alternative pathway, the conversion of putrescine into GABA, also contributes to GABA synthesis. We show here that GAD immunoreactivity is not significantly detectable within the SVZ/RMS. However, strong immunolabeling is found within the OB. Nevertheless, low GAD enzymatic activity (as compared with OB) is detected in the SVZ/RMS. SVZ/RMS explants convert approximately 30% of all captured radiolabeled putrescine into GABA in vitro, showing that this pathway is important for GABA synthesis in the SVZ. We also show that SVZ/RMS, OB and choroid plexus explants are able to synthesize putrescine, as analyzed by ornithine decarboxylase (ODC) activity, providing neuroblasts with different sources of putrescine for GABA production. During early stages of neuroblast differentiation, in which neurotransmitter choice may still be undefined, an alternative pathway for GABA synthesis guarantees the production of GABA, necessary for neuroblast proliferation and migration in the SVZ/RMS.     

Adult neural stem cells from the mouse subventricular zone are limited in migratory ability compared to progenitor cells of similar origin

The subventricular zone (SVZ) in the forebrain is the largest source of neural stem cells and progenitor cells in the adult CNS. To assess the ability of adult neural stem cells to survive, differentiate and migrate, we have compared the behavior of dissociated, neurosphere-derived stem cells with that of progenitor cells in transplantation experiments. This ability was first tested in vivo, offering the stem cells the possibility to migrate along the rostral migratory stream (RMS), their specific pathway. In addition, the differential behaviors of the two classes of cells were also compared in vitro by grafting them into organotypic slice cultures containing either tangential (embryonic cerebral cortex) or radial (early postnatal cerebellar cortex) migratory routes. Most of the grafted adult neurosphere-derived stem cells survived and integrated in vivo, and a proportion of them differentiate into neurons, oligodendrocytes or astrocytes. However, they were unable to migrate along the RMS and remained in the vicinity of the injection site. In contrast, SVZ progenitor cells were able to migrate toward the olfactory bulb and, once there, to acquire the phenotype of granule cells, as previously reported. In vitro, neural stem cells exhibited a better migratory ability, although they only migrated for short distances, particularly, in forebrain slices. Nevertheless, the average distance covered by progenitor cells was a two-fold longer than that covered by neural stem cells, corroborating that this class of more specified cells has higher migratory ability. These results suggest that the in vitro conditions of expanding SVZ-derived stem cells, required to maintain them in an immature stage might modify their intrinsic properties, preventing their differentiation into neuroblasts and their subsequent migration.     

Expression of drebrin E in migrating neuroblasts in adult rat brain: coincidence between drebrin E disappearance from cell body and cessation of migration

Migrating neuroblasts in the adult brain form the rostral migratory stream (RMS) from the lateral ventricle to the olfactory bulb (OB) and then differentiate in the OB. In this study, we immunohistochemically analyzed drebrin expression in the RMS of the adult rat brain. Although drebrin is concentrated in dendritic spines of mature neurons, drebrin-immunopositive (DIP) cell bodies were observed in the RMS. The polysialated form of a neural cell adhesion molecule (PSA-NCAM) was detected in DIP cells. K(i)-67, a marker of proliferating cells, was also detected in a subset of DIP cells; however, neither glial fibrillary acidic protein, nestin nor vimentin was detected in DIP cells. These results indicate that DIP cells in the RMS are migrating neuroblasts. An image subtraction method, based on using anti-pan-drebrin and anti-drebrin A antibodies, demonstrated that DIP migrating neuroblasts are immunopositive for drebrin E but not for drebrin A (E+A-). Furthermore, olfactory bulbectomy increased the number of cells with drebrin E+A- signals in the RMS, indicating that these cells migrate along the RMS. Drebrin E+A- cells were also found in the subgranular layer of the dentate gyrus and in the piriform cortex. Thus, detection of drebrin E+A- signals is useful for identifying migrating neuroblasts in the adult brain. In the OB, drebrin E+A- signals were observed in the cell bodies of migrating neuroblasts in the core region; however, only fibrous and punctate drebrin E+A- signals were observed in postmigratory neuroblasts at the outer layers. These data demonstrate that the disappearance of drebrin E+A- signals from the cell body coincides with the cessation of neuronal migration. The disappearance of drebrin E from the cell body may be a molecular switch for the cessation of migration in newly generated neuroblasts.     

Expression of ezrin in glial tubes in the adult subventricular zone and rostral migratory stream

Ezrin is a member of the ERM (ezrin-radixin-moesin) family of membrane-cytoskeletal linking proteins. ERM proteins are involved in a wide variety of cellular functions including cell motility, signal transduction, cell-cell interaction and cell-matrix recognition. A recent in situ hybridization study showed that the mRNA encoding ezrin is expressed in neurogenic regions of the mature brain including the subventricular zone (SVZ) and rostral migratory stream (RMS); however, the specific cell types expressing ezrin and their relationship to migrating and proliferating cells in these regions have not been characterized previously. In this study, we used immunocytochemistry to perform double labeling with a variety of cell-type specific markers to characterize the expression of ezrin in the SVZ and RMS of adult mice. Ezrin was expressed at high levels in both the SVZ and RMS where ezrin-immunopositive processes formed a trabecular network surrounding the proliferating and migrating cells. Ezrin-positive cells co-labeled with the glial makers S100beta and GFAP (glial fibrillary acidic protein), but only minimally with the early neuronal markers beta III tubulin and polysialylated form of neural cell adhesion molecule 1 (PSA-NCAM), indicating that ezrin was expressed primarily in the glial tube cells. Ezrin positive cells also expressed beta-catenin, a membrane-complex protein previously implicated in the regulation of stem-cell proliferation and neuronal migration. Glial tube cells act as both precursors of, and a physical channel for, migrating neuroblasts. Bi-directional signals between glial tube cells and migrating neuroblasts have been shown to regulate the rates of both proliferation of the precursor cells and migration of the newly generated neuroblasts. Our finding that ezrin and beta-catenin are both present at the cell membrane of the glial tube cells suggests that these proteins may be involved in those signaling processes.     

Age-dependent regional changes in the rostral migratory stream

Throughout life the subventricular zone (SVZ) is a source of new olfactory bulb (OB) interneurons. From the SVZ, neuroblasts migrate tangentially through the rostral migratory stream (RMS), a restricted route approximately 5 mm long in mice, reaching the OB within 10–14 days. Within the OB, neuroblasts migrate radially to the granule and glomerular layers where they differentiate into granule and periglomerular (PG) cells and integrate into existing synaptic circuits. SVZ neurogenesis decreases with age, and might be a factor in age-related olfactory deficits. However, the effect of aging on the RMS and on the differentiation of interneuron subpopulations remains poorly understood. Here, we examine RMS cytoarchitecture, neuroblast proliferation and clearance from the RMS, and PG cell subpopulations at 6, 12, 18, and 23 months of age. We find that aging affects the area occupied by newly generated cells within the RMS and regional proliferation, and the clearance of neuroblasts from the RMS and PG cell subpopulations and distribution remain stable.     

Temporal profile of subventricular zone progenitor cell migration following quinolinic acid-induced striatal cell loss

A number of studies have demonstrated directed migration of neural progenitor cells to sites of brain injury and disease, however a detailed examination of when a cell is "born" in relation to injury induction and the migratory response of that cell has not previously been determined. This study therefore examined the temporal correlation between progenitor cell proliferation ("birth") and neuroblast migratory response into the damaged striatum following quinolinic acid (QA) lesioning of the adult rat striatum. Retroviral labeling of subventricular zone (SVZ)-derived progenitor cells demonstrated that cell loss in the QA-lesioned striatum increased progenitor cell migration through the rostral migratory stream (RMS) for up to 30 days. In addition, a population of dividing cells originating from the SVZ generated doublecortin positive neuroblasts that migrated into the damaged striatum in response to cell loss invoked by the QA lesion. Quantification of bromodeoxyuridine (BrdU)-labeled cells co-expressing doublecortin revealed that the majority of cells present in the damaged striatum were generated from progenitor cells dividing within 2 days either prior to or following the QA lesion. In contrast, cells dividing 2 or more days following QA lesioning, migrated into the striatum and exhibited a glial phenotype. These results demonstrate that directed migration of SVZ-derived cells and neuroblast differentiation in response to QA lesioning of the striatum is acute and transient. We propose this is predominantly due to a reduced capacity over time for newly generated neuroblasts to respond to the lesioned environment due to a loss or inhibition of migratory cues.     

The cellular composition and morphological organization of the rostral migratory stream in the adult human brain

The rostral migratory stream (RMS) is the major pathway by which progenitor cells migrate from the subventricular zone (SVZ) to the olfactory bulb (OB) in rodents, rabbits and primates. However, the existence of an RMS within the adult human brain has been elusive. Immunohistochemical studies utilising cell-type specific markers for early progenitor cells (CD133), proliferating cells (PCNA), astrocytes and type B cells (GFAP) and migrating neuroblasts (PSA-NCAM), reveal that the adult human RMS is organized into layers containing glial cells, proliferating cells and neuroblasts. In addition, the RMS is arranged around a remnant of the ventricular cavity that extends from the SVZ to the OB as seen by immunohistological staining analysis and electron microscopy, showing the presence of basal bodies and a typical 9 + 2 arrangement of tubulin in tufts of cilia from all levels of the RMS. Overall, these findings suggest that a pathway of migratory progenitor cells similar to that seen in other mammals is present within the adult human brain and that this pathway could provide for neurogenesis in the human forebrain. These findings contribute to the scientific understanding of adult neurogenesis and establish the detailed cytoarchitecture of this novel neurogenic niche in the human brain.     

Disruption of Eph/ephrin signaling affects migration and proliferation in the adult subventricular zone

The subventricular zone (SVZ) of the lateral ventricles, the largest remaining germinal zone of the adult mammalian brain, contains an extensive network of neuroblasts migrating rostrally to the olfactory bulb. Little is known about the endogenous proliferation signals for SVZ neural stem cells or guidance cues along the migration pathway. Here we show that the receptor tyrosine kinases EphB1-3 and EphA4 and their transmembrane ligands, ephrins-B2/3, are expressed by cells of the SVZ. Electron microscopy revealed ephrin-B ligands associated with SVZ astrocytes, which function as stem cells in this germinal zone. A three-day infusion of the ectodomain of either EphB2 or ephrin-B2 into the lateral ventricle disrupted migration of neuroblasts and increased cell proliferation. These results suggest that Eph/ephrin signaling is involved in the migration of neuroblasts in the adult SVZ and in either direct or indirect regulation of cell proliferation.     

喙端迁移流的发生及其细胞凋亡

目的 研究生后不同日龄小鼠喙端迁移流（RMS）的发育,神经干细胞增殖和凋亡的规律。方法 利用Caspase-8免疫荧光标记法和5’-溴脱氧尿嘧啶核苷（BrdU）法,对小鼠RMS内的神经干细胞增殖和凋亡进行研究（n =92）。结果 生后早期小鼠脑内,尤其是室管下区（SVZ）和RMS,存在大量的增殖细胞。随着小鼠年龄的增加,脑内干细胞逐渐减少,到成年,大脑皮质几乎见不到增殖的神经干细胞,但在SVZ和RMS仍可以看到许多增殖的神经干细胞。在RMS,神经干细胞增殖的同时伴随着细胞凋亡,干细胞的增殖与凋亡存在着正相关关系。结论 RMS的神经干细胞增殖与凋亡有重要的生理意义,通过细胞凋亡,RMS可以调节神经干细胞向嗅球迁移的数量,也可以调节干细胞向颗粒细胞分化。     

BM88/Cend1 expression levels are critical for proliferation and differentiation of subventricular zone-derived neural precursor cells

Neural stem cells remain in two areas of the adult mammalian brain, the subventricular zone (SVZ) and the dentate gyrus of the hippocampus. Ongoing neurogenesis via the SVZ-rostral migratory stream pathway maintains neuronal replacement in the olfactory bulb (OB) throughout life. The mechanisms determining how neurogenesis is restricted to only a few regions in the adult, in contrast to its more widespread location during embryogenesis, largely depend on controlling the balance between precursor cell proliferation and differentiation. BM88/Cend1 is a neuronal lineage-specific regulator implicated in cell cycle exit and differentiation of precursor cells in the embryonic neural tube. Here we investigated its role in postnatal neurogenesis. Study of in vivo BM88/Cend1 distribution revealed that it is expressed in low levels in neuronal precursors of the adult SVZ and in high levels in postmitotic OB interneurons. To assess the functional significance of BM88/Cend1 in neuronal lineage progression postnatally, we challenged its expression levels by gain- and loss-of-function approaches using lentiviral gene transfer in SVZ-derived neurospheres. We found that BM88/Cend1 overexpression decreases proliferation and favors neuronal differentiation, whereas its downregulation using new-generation RNA interference vectors yields an opposite phenotype. Our results demonstrate that BM88/Cend1 participates in cell cycle control and neuronal differentiation mechanisms during neonatal SVZ neurogenesis and becomes crucial for the transition from neuroblasts to mature neurons when reaching high levels.     

Dynamic imaging reveals that brain-derived neurotrophic factor can independently regulate motility and direction of neuroblasts within the rostral migratory stream

Neuronal precursors generated in the subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB). Although, the mechanisms regulating this migration remain largely unknown. Studies have shown that molecular factors, such as brain-derived neurotrophic factor (BDNF) emanating from the OB, may function as chemoattractants drawing neuroblasts toward their target. To better understand the role of BDNF in RMS migration, we used an acute slice preparation from early postnatal mice to track the tangential migration of GAD65-GFP labeled RMS neuroblasts with confocal time-lapse imaging. By quantifying the cell dynamics using specific directional and motility criteria, our results showed that removal of the OB did not alter the overall directional trajectory of neuroblasts, but did reduce their motility. This suggested that additional guidance factors present locally within the RMS region also contribute to this migration. Here we report that BDNF and its high affinity receptor, tyrosine kinase receptor type 2 (TrkB), are indeed heterogeneously expressed within the RMS at postnatal day 7. By altering BDNF levels within the entire pathway, we showed that reduced BDNF signaling changes both neuroblast motility and direction, while increased BDNF levels changes only motility. Together these data reveal that during this early postnatal period BDNF plays a complex role in regulating both the motility and direction of RMS flow, and that BDNF comes from sources within the RMS itself, as well as from the olfactory bulb.     

Ionizing radiation enhances the engraftment of transplanted in vitro-derived multipotent astrocytic stem cells

The subependymal zone (SEZ) is a region of persistent neurogenesis in the adult mammalian brain containing a neural stem cell (NSC) pool that continuously generates migratory neuroblasts that travel in chains through the rostral migratory stream (RMS) to the olfactory bulb (OB), where they differentiate and functionally integrate into existing neural circuitry. NSCs can be isolated from the SEZ and cultured to generate either neurospheres (NSs) or multipotent astrocytic stem cells (MASCs), with both possessing the stem cell characteristics of multipotency and self-renewal. NSs and MASCs home to the SEZ after transplantation into the lateral ventricle (LV) and contribute to neuroblast migration, with minimal engraftment into the OB observed in the adult mouse. Recent studies have compared the relatively uncharacterized NSC with the more established hematopoietic stem cell (HSC) in an effort to determine the level of stemness possessed by the NSC. Depletion of native HSCs in the bone marrow by lethal irradiation (LI) is necessary to maximize functional engraftment of donor HSCs. Our data show that the NSC pool and neuroblasts in the SEZ can be significantly and permanently depleted by exposure to LI. Attenuation of donor-derived migratory neuroblast engraftment into the OB is observed after transplantation of gfp+ MASCs into the LV of LI animals, whereas engraftment is significantly enhanced after transplantation into animals exposed to sublethal levels of ionizing radiation. By increasing receptiveness of the NSC niche through depletion of indigenous cells, the adult SEZ-RMS-OB can be used as a model to further characterize the NSC.     

Expression of amyloid precursor protein-like molecule in astroglial cells of the subventricular zone and rostral migratory stream of the adult rat forebrain

In adult mammals, new neurons in the subventricular zone (SVZ) of the lateral ventricle (LV) migrate tangentially through the rostral migratory stream (RMS) to the olfactory bulb (OB), where they mature into local interneurons. Using a monoclonal antibody for the beta-amyloid precursor protein (APP) (mAb 22C11), which is specific for the amino-terminal region of the secreted form of APP and recognizes all APP isoforms and APP-related proteins, immunoreactivity was detected in specific subpopulations of cells in the SVZ and RMS of the adult rat forebrain. In the SVZ, APP-like immunoreactivity was detected in the ependymal cells lining the LV and some of the subependymal cells. The latter were regarded as astrocytes, because they were positive for the glial markers, S-100 protein (S-100) and glial fibrillary acidic protein (GFAP). APP-like immunoreactive astrocytes exhibited strong labelling of the perinuclear cytoplasm and often possessed a long, fine process similar to that found with radial glia. The process extended to an APP-like immunoreactive meshwork in the RMS that consisted of cytoplasmic processes of astrocytes forming 'glial tubes'. Double-immunofluorescent labelling with a highly polysialylated neural cell adhesion molecule (PSA-NCAM) confirmed that the APP-like immunoreactive astrocytes in the SVZ and meshwork in the RMS made close contact with PSA-NCAM-immunopositive neuroblasts, suggesting an interaction between APP-containing cells and neuroblasts. This region of the adult brain is a useful in vivo model to investigate the role of APP in neurogenesis.     

Conditional ablation of Tbr2 results in abnormal development of the olfactory bulbs and subventricular zone‐rostral migratory stream

Development of the olfactory bulb (OB) is a complex process that requires contributions from several progenitor cell niches to generate neuronal diversity. Previous studies showed that Tbr2 is expressed during the generation of glutamatergic OB neurons in rodents. However, relatively little is known about the role of Tbr2 in the developing OB or in the subventricular zone‐rostral migratory stream (SVZ‐RMS) germinal niche that gives rise to many OB neurons. Results: Here, we use conditional gene ablation strategies to knockout Tbr2 during embryonic mouse olfactory bulb morphogenesis, as well as during perinatal and adult neurogenesis from the SVZ‐RMS niche, and describe the resulting phenotypes. We find that Tbr2 is important for the generation of mitral cells in the OB, and that the olfactory bulbs themselves are hypoplastic and disorganized in Tbr2 mutant mice. Furthermore, we show that the SVZ‐RMS niche is expanded and disordered following loss of Tbr2, which leads to ectopic accumulation of neuroblasts in the RMS. Lastly, we show that adult glutamatergic neurogenesis from the SVZ is impaired by loss of Tbr2. Conclusions: Tbr2 is essential for proper morphogenesis of the OB and SVZ‐RMS, and is important for the generation of multiple lineages of glutamatergic olfactory bulb neurons. Developmental Dynamics 243:440–450, 2014. © 2013 Wiley Periodicals, Inc.     

Deprivation of sensory inputs to the olfactory bulb up-regulates cell death and proliferation in the subventricular zone of adult mice

The main olfactory bulb (MOB) is the first relay on the olfactory sensory pathway and the target of the neural progenitor cells generated in the subventricular zone (SVZ) lining the lateral ventricles and which migrate along the rostral extension of the SVZ, also called the rostral migratory stream (RMS). Within the MOB, the neuroblasts differentiate into granular and periglomerular interneurons. A reduction in the number of granule cells during sensory deprivation suggests that neurogenesis may be influenced by afferent activity. Here, we show that unilateral sensory deafferentation of the MOB by axotomy of the olfactory receptor neurons increases apoptotic cell death in the SVZ and along the rostro-caudal extent of the RMS. The vast majority of dying cells in the RMS are migrating neuroblasts as indicated by double Terminal deoxynucleotidyl transferase-mediated biotinylated UTP nick-end labeling/PSA-NCAM labeling. Counting bromodeoxyuridine-labeled cells in animals killed immediately or 4 days after tracer administration showed a bilateral increase in proliferation in the SVZ and RMS which was balanced by cell death on the operated side. These data suggest that olfactory inputs are required for the survival of newborn neural progenitors. The greatest enhancement in proliferation occurred in the extension of the RMS located in the MOB, revealing a population of local precursors mitotically stimulated following axotomy. Together, these findings indicate that olfactory inputs may strongly modulate the balance between neurogenesis and apoptosis in the SVZ and RMS and provide a model for further investigation of the underlying molecular mechanisms of this activity-dependent neuronal plasticity.     

The rostral migratory stream is a neurogenic niche that predominantly engenders periglomerular cells: in vivo evidence in the adult rat brain

In vitro studies support the existence of adult neural stem cells in the rostral migratory stream (RMS). The evidence supporting this possibility in vivo is scarce. We then explore this issue by taking advantage of a rat model in which a physical barrier implanted in the brain interrupted the migration of neuroblasts derived from the SVZ along the RMS at the level of its vertical limb. The presence of local stem cells and neurogenesis were then established by estimating the number of nuclei labeled with bromo-deoxyuridine (BrdU), the number of doublecortin-positive neuroblasts and the existence of cells displaying co-localization of BrdU and Sox-2 immunoreactivity along the RMS, at different time points following barrier implantation. Estimations of the number of the granular and periglomerular neurons integrated into the corresponding layers of the olfactory bulb of implanted rats established that stem cells in the RMS give rise predominantly to periglomerular neurons. Our results then support the notion that the RMS is indeed a region in which neurogenesis is taking place in the adult brain. They also support that the relative location of the neurogenic niche might imprint, at least in some degree, the identity and lineage of the neuroblasts arising from them.     

Expression of ezrin radixin moesin proteins in the adult subventricular zone and the rostral migratory stream

Continuous proliferation occurs in the adult subventricular zone (SVZ) of the lateral ventricles throughout life. In the SVZ, progenitor cells differentiate into neuroblasts, which migrate tangentially along the rostral migratory stream (RMS) to reach their final destination in the olfactory bulb. These progenitor cells mature and integrate into the existing neural network of the olfactory bulb. Long distance migration of neuroblasts in the RMS requires a highly dynamic cytoskeleton with the ability to respond to surrounding stimuli. Radixin is a member of the ERM (Ezrin, Radixin, Moesin) family, which connect the actin cytoskeleton to the extracellular matrix through transmembrane proteins. The membrane-cytoskeleton linker proteins of the ERM family may regulate cellular events with a high demand on cytoskeleton plasticity, such as cell motility. Recently, specific expression of the ERM protein ezrin was shown in the RMS. Radixin however has not been characterized in this region. Here we used immunohistochemistry and confocal microscopy to examine the expression of radixin in the different cell types of the adult subventricular zone niche and in the RMS. Our findings indicate that radixin is strongly expressed in neuroblasts of the adult RMS and subventricular zone, and also in Olig2-positive cells. We also demonstrate the presence of radixin in the cerebral cortex, striatum, cerebellum, thalamus, hippocampus as well as the granular and periglomerular layers of the olfactory bulb. Our studies also reveal the localization of radixin in neurosphere culture studies and we reveal the specificity of our labeling using Western blotting. The expression pattern demonstrated here suggests a role for radixin in neuronal migration and differentiation in the adult RMS. Understanding how adult neuronal migration is regulated is of importance for the development of new therapeutic interventions using endogenous repair for neurodegenerative diseases.     

Anosmin-1 over-expression increases adult neurogenesis in the subventricular zone and neuroblast migration to the olfactory bulb

New subventricular zone (SVZ)-derived neuroblasts that migrate via the rostral migratory stream are continuously added to the olfactory bulb (OB) of the adult rodent brain. Anosmin-1 (A1) is an extracellular matrix protein that binds to FGF receptor 1 (FGFR1) to exert its biological effects. When mutated as in Kallmann syndrome patients, A1 is associated with severe OB morphogenesis defects leading to anosmia and hypogonadotropic hypogonadism. Here, we show that A1 over-expression in adult mice strongly increases proliferation in the SVZ, mainly with symmetrical divisions, and produces substantial morphological changes in the normal SVZ architecture, where we also report the presence of FGFR1 in almost all SVZ cells. Interestingly, for the first time we show FGFR1 expression in the basal body of primary cilia in neural progenitor cells. Additionally, we have found that A1 over-expression also enhances neuroblast motility, mainly through FGFR1 activity. Together, these changes lead to a selective increase in several GABAergic interneuron populations in different OB layers. These specific alterations in the OB would be sufficient to disrupt the normal processing of sensory information and consequently alter olfactory memory. In summary, this work shows that FGFR1-mediated A1 activity plays a crucial role in the continuous remodelling of the adult OB