Adult mouse subventricular zone stem and progenitor cells are sessile and epidermal growth factor receptor negatively regulates neuroblast migration

Subventricular zone stem cell niche injury is associated with intestinal perforation in preterm infants and predicts future motor impairment

Brain injury is highly associated with preterm birth. Complications of prematurity, including spontaneous or necrotizing enterocolitis (NEC)-associated intestinal perforations, are linked to lifelong neurologic impairment, yet the mechanisms are poorly understood. Early diagnosis of preterm brain injuries remains a significant challenge. Here, we identified subventricular zone echogenicity (SVE) on cranial ultrasound in preterm infants following intestinal perforations. The development of SVE was significantly associated with motor impairment at 2 years. SVE was replicated in a neonatal mouse model of intestinal perforation. Examination of the murine echogenic subventricular zone (SVZ) revealed NLRP3-inflammasome assembly in multiciliated FoxJ1+ ependymal cells and a loss of the ependymal border in this postnatal stem cell niche. These data suggest a mechanism of preterm brain injury localized to the SVZ that has not been adequately considered. Ultrasound detection of SVE may serve as an early biomarker for neurodevelopmental impairment after inflammatory disease in preterm infants.

Targeting epidermal growth factor receptor to recruit newly generated neuroblasts in cortical brain injuries

BACKGROUND

Neurogenesis is stimulated in the subventricular zone (SVZ) of mice with cortical brain injuries. In most of these injuries, newly generated neuroblasts attempt to migrate toward the injury, accumulating within the corpus callosum not reaching the perilesional area.

METHODS

We use a murine model of mechanical cortical brain injury, in which we perform unilateral cortical injuries in the primary motor cortex of adult male mice. We study neurogenesis in the SVZ and perilesional area at 7 and 14 dpi as well as the expression and concentration of the signaling molecule transforming growth factor alpha (TGF-α) and its receptor the epidermal growth factor (EGFR). We use the EGFR inhibitor Afatinib to promote neurogenesis in brain injuries.

RESULTS

We show that microglial cells that emerge within the injured area and the SVZ in response to the injury express high levels of TGF-α leading to elevated concentrations of TGF-α in the cerebrospinal fluid. Thus, the number of neuroblasts in the SVZ increases in response to the injury, a large number of these neuroblasts remain immature and proliferate expressing the epidermal growth factor receptor (EGFR) and the proliferation marker Ki67. Restraining TGF-α release with a classical protein kinase C inhibitor reduces the number of these proliferative EGFR+ immature neuroblasts in the SVZ. In accordance, the inhibition of the TGF-α receptor, EGFR promotes migration of neuroblasts toward the injury leading to an elevated number of neuroblasts within the perilesional area.

CONCLUSIONS

Our results indicate that in response to an injury, microglial cells activated within the injury and the SVZ release TGF-α, activating the EGFR present in the neuroblasts membrane inducing their proliferation, delaying maturation and negatively regulating migration. The inactivation of this signaling pathway stimulates neuroblast migration toward the injury and enhances the quantity of neuroblasts within the injured area. These results suggest that these proteins may be used as target molecules to regenerate brain injuries.

Serotonergic mediation of the brain-wide neurogenesis: Region-dependent and receptor-type specific roles on neurogenic cellular transformation

Brain serotonin (5-hydroxytryptamine, 5-HT) is a key molecule for the mediation of depression-related brain states, but the neural mechanisms underlying 5-HT mediation need further investigation. A possible mechanism of the therapeutic antidepressant effects is neurogenic cell production, as stimulated by 5-HT signaling. Neurogenesis, the proliferation of neural stem cells (NSCs), and cell differentiation and maturation occur across brain regions, particularly the hippocampal dentate gyrus and the subventricular zone, throughout one's lifespan. 5-HT plays a major role in the mediation of neurogenic processes, which in turn leads to the therapeutic effect on depression-related states. In this review article, we aim to identify how the neuronal 5-HT system mediates the process of neurogenesis, including cell proliferation, cell-type differentiation and maturation. First, we will provide an overview of the neurogenic cell transformation that occurs in brain regions containing or lacking NSCs. Second, we will review brain region-specific mechanisms of 5-HT-mediated neurogenesis by comparing regions localized to NSCs, i.e., the hippocampus and subventricular zone, with those not containing NSCs. Highlighting these 5-HT mechanisms that mediate neurogenic cell production processes in a brain-region-specific manner would provide unique insights into the role of 5-HT in neurogenesis and its associated effects on depression.

4D imaging analysis of the aging mouse neural stem cell niche reveals a dramatic loss of progenitor cell dynamism regulated by the RHO-ROCK pathway

In the adult ventricular-subventricular zone (V-SVZ), neural stem cells (NSCs) give rise to transit-amplifying progenitor (TAP) cells. These progenitors reside in different subniche locations, implying that cell movement must accompany lineage progression, but the dynamic behaviors of adult NSCs and TAPs remain largely unexplored. Here, we performed live time-lapse imaging with computer-based image analysis of young and aged 3D V-SVZ wholemounts from transgenic mice with fluorescently distinguished NSCs and TAP cells. Young V-SVZ progenitors are highly dynamic, with regular process outgrowth and retraction and cell migration. However, these activities dramatically declined with age. An examination of single-cell RNA sequencing (RNA-seq) data revealed age-associated changes in the Rho-Rock pathway that are important for cell motility. Applying a small molecule to inhibit ROCK transformed young into old V-SVZ progenitor cell dynamic behaviors. Hence RHO-ROCK signaling is critical for normal adult NSC and TAP movement and interactions, which are compromised with age, concomitant with the loss of regenerative ability.

Impaired Generation of Transit-Amplifying Progenitors in the Adult Subventricular Zone of Cyclin D2 Knockout Mice

In the adult brain, new neurons are constitutively derived from postnatal neural stem cells/progenitors located in two neurogenic regions: the subventricular zone (SVZ) of the lateral ventricles (migrating and differentiating into different subtypes of the inhibitory interneurons of the olfactory bulbs), and the subgranular layer of the hippocampal dentate gyrus. Cyclin D2 knockout (cD2-KO) mice exhibit reduced numbers of new hippocampal neurons; however, the proliferation deficiency and the dysregulation of adult neurogenesis in the SVZ required further investigation. In this report, we characterized the differentiation potential of each subpopulation of the SVZ neural precursors in cD2-KO mice. The number of newly generated cells in the SVZs was significantly decreased in cD2-KO mice compared to wild type mice (WT), and was not accompanied by elevated levels of apoptosis. Although the number of B1-type quiescent precursors (B1q) and the overall B1-type activated precursors (B1a) were not affected in the SVZ neurogenic niche, the number of transit-amplifying progenitors (TaPs) was significantly reduced. Additionally, the subpopulations of calbindin D28k and calretinin interneurons were diminished in the olfactory bulbs of cD2-KO mice. Our results suggest that cyclin D2 might be critical for the proliferation of neural precursors and progenitors in the SVZ—the transition of B1a into TaPs and, thereafter, the production of newly generated interneurons in the olfactory bulbs. Untangling regulators that functionally modulate adult neurogenesis provides a basis for the development of regenerative therapies for injuries and neurodegenerative diseases.

Novel Galectin-3 Roles in Neurogenesis, Inflammation and Neurological Diseases

Galectin-3 (Gal-3) is an evolutionarily conserved and multifunctional protein that drives inflammation in disease. Gal-3's role in the central nervous system has been less studied than in the immune system. However, recent studies show it exacerbates Alzheimer's disease and is upregulated in a large variety of brain injuries, while loss of Gal-3 function can diminish symptoms of neurodegenerative diseases such as Alzheimer's. Several novel molecular pathways for Gal-3 were recently uncovered. It is a natural ligand for TREM2 (triggering receptor expressed on myeloid cells), TLR4 (Toll-like receptor 4), and IR (insulin receptor). Gal-3 regulates a number of pathways including stimulation of bone morphogenetic protein (BMP) signaling and modulating Wnt signalling in a context-dependent manner. Gal-3 typically acts in pathology but is now known to affect subventricular zone (SVZ) neurogenesis and gliogenesis in the healthy brain. Despite its myriad interactors, Gal-3 has surprisingly specific and important functions in regulating SVZ neurogenesis in disease. Gal-1, a similar lectin often co-expressed with Gal-3, also has profound effects on brain pathology and adult neurogenesis. Remarkably, Gal-3's carbohydrate recognition domain bears structural similarity to the SARS-CoV-2 virus spike protein necessary for cell entry. Gal-3 can be targeted pharmacologically and is a valid target for several diseases involving brain inflammation. The wealth of molecular pathways now known further suggest its modulation could be therapeutically useful.

Adult neural stem cell activation in mice is regulated by the day/night cycle and intracellular calcium dynamics

Neural stem cells (NSCs) in the adult brain transit from the quiescent state to proliferation to produce new neurons. The mechanisms regulating this transition in freely behaving animals are, however, poorly understood. We customized in vivo imaging protocols to follow NSCs for several days up to months, observing their activation kinetics in freely behaving mice. Strikingly, NSC division is more frequent during daylight and is inhibited by darkness-induced melatonin signaling. The inhibition of melatonin receptors affected intracellular Ca²⁺ dynamics and promoted NSC activation. We further discovered a Ca²⁺ signature of quiescent versus activated NSCs and showed that several microenvironmental signals converge on intracellular Ca²⁺ pathways to regulate NSC quiescence and activation. In vivo NSC-specific optogenetic modulation of Ca²⁺ fluxes to mimic quiescent-state-like Ca²⁺ dynamics in freely behaving mice blocked NSC activation and maintained their quiescence, pointing to the regulatory mechanisms mediating NSC activation in freely behaving animals.

A Semi-automated and Scalable 3D Spheroid Assay to Study Neuroblast Migration

The subventricular zone of the mammalian brain is the major source of adult born neurons. These neuroblasts normally migrate long distances to the olfactory bulbs but can be re-routed to locations of injury and promote neuroregeneration. Mechanistic understanding and pharmacological targets regulating neuroblast migration is sparse. Furthermore, lack of migration assays limits development of pharmaceutical interventions targeting neuroblast recruitment. We therefore developed a physiologically relevant 3D neuroblast spheroid migration assay that permits the investigation of large numbers of interventions. To verify the assay, 1,012 kinase inhibitors were screened for their effects on migration. Several induced significant increases or decreases in migration. MuSK and PIK3CB were selected as putative targets and their knockdown validated increased neuroblast migration. Thus, compounds identified through this assay system could be explored for their potential in augmenting neuroblast recruitment to sites of injury for neuroregeneration, or for decreasing malignant invasion.

Tissue Engineering and Biomaterial Strategies to Elicit Endogenous Neuronal Replacement in the Brain

Neurogenesis in the postnatal mammalian brain is known to occur in the dentate gyrus of the hippocampus and the subventricular zone. These neurogenic niches serve as endogenous sources of neural precursor cells that could potentially replace neurons that have been lost or damaged throughout the brain. As an example, manipulation of the subventricular zone to augment neurogenesis has become a popular strategy for attempting to replace neurons that have been lost due to acute brain injury or neurodegenerative disease. In this review article, we describe current experimental strategies to enhance the regenerative potential of endogenous neural precursor cell sources by enhancing cell proliferation in neurogenic regions and/or redirecting migration, including pharmacological, biomaterial, and tissue engineering strategies. In particular, we discuss a novel replacement strategy based on exogenously biofabricated "living scaffolds" that could enhance and redirect endogenous neuroblast migration from the subventricular zone to specified regions throughout the brain. This approach utilizes the first implantable, biomimetic tissue-engineered rostral migratory stream, thereby leveraging the brain's natural mechanism for sustained neuronal replacement by replicating the structure and function of the native rostral migratory stream. Across all these strategies, we discuss several challenges that need to be overcome to successfully harness endogenous neural precursor cells to promote nervous system repair and functional restoration. With further development, the diverse and innovative tissue engineering and biomaterial strategies explored in this review have the potential to facilitate functional neuronal replacement to mitigate neurological and psychiatric symptoms caused by injury, developmental disorders, or neurodegenerative disease.

A novel PKC activating molecule promotes neuroblast differentiation and delivery of newborn neurons in brain injuries

Neural stem cells are activated within neurogenic niches in response to brain injuries. This results in the production of neuroblasts, which unsuccessfully attempt to migrate toward the damaged tissue. Injuries constitute a gliogenic/non-neurogenic niche generated by the presence of anti-neurogenic signals, which impair neuronal differentiation and migration. Kinases of the protein kinase C (PKC) family mediate the release of growth factors that participate in different steps of the neurogenic process, particularly, novel PKC isozymes facilitate the release of the neurogenic growth factor neuregulin. We have demonstrated herein that a plant derived diterpene, (EOF2; CAS number 2230806-06-9), with the capacity to activate PKC facilitates the release of neuregulin 1, and promotes neuroblasts differentiation and survival in cultures of subventricular zone (SVZ) isolated cells in a novel PKC dependent manner. Local infusion of this compound in mechanical cortical injuries induces neuroblast enrichment within the perilesional area, and noninvasive intranasal administration of EOF2 promotes migration of neuroblasts from the SVZ towards the injury, allowing their survival and differentiation into mature neurons, being some of them cholinergic and GABAergic. Our results elucidate the mechanism of EOF2 promoting neurogenesis in injuries and highlight the role of novel PKC isozymes as targets in brain injury regeneration.

Transgenic models for investigating the nervous system: Currently available neurofluorescent reporters and potential neuronal markers

Recombinant DNA technologies have enabled the development of transgenic animal models for use in studying a myriad of diseases and biological states. By placing fluorescent reporters under the direct regulation of the promoter region of specific marker proteins, these models can localize and characterize very specific cell types. One important application of transgenic species is the study of the cytoarchitecture of the nervous system. Neurofluorescent reporters can be used to study the structural patterns of nerves in the central or peripheral nervous system in vivo, as well as phenomena involving embryologic or adult neurogenesis, injury, degeneration, and recovery. Furthermore, crucial molecular factors can also be screened via the transgenic approach, which may eventually play a major role in the development of therapeutic strategies against diseases like Alzheimer's or Parkinson's. This review describes currently available reporters and their uses in the literature as well as potential neural markers that can be leveraged to create additional, robust transgenic models for future studies.

The role of inflammation in subventricular zone cancer

The adult subventricular zone (SVZ) stem cell niche has proven vital for discovering neurodevelopmental mechanisms and holds great potential in medicine for neurodegenerative diseases. Yet the SVZ holds a dark side - it can become tumorigenic. Glioblastomas can arise from the SVZ via cancer stem cells (CSCs). Glioblastoma and other brain cancers often have dismal prognoses since they are resistant to treatment. In this review we argue that the SVZ is susceptible to cancer because it contains stem cells, migratory progenitors and unusual inflammation. Theoretically, SVZ stem cells can convert to CSCs more readily than can postmitotic neural cells. Additionally, the robust long-distance migration of SVZ progenitors can be subverted upon tumorigenesis to an infiltrative phenotype. There is evidence that the SVZ, even in health, exhibits chronic low-grade cellular and molecular inflammation. Its inflammatory response to brain injuries and disease differs from that of other brain regions. We hypothesize that the SVZ inflammatory environment can predispose cells to novel mutations and exacerbate cancer phenotypes. This can be studied in animal models in which human mutations related to cancer are knocked into the SVZ to induce tumorigenesis and the CSC immune interactions that precede full-blown cancer. Importantly inflammation can be pharmacologically modulated providing an avenue to brain cancer management and treatment. The SVZ is accessible by virtue of its location surrounding the lateral ventricles and CSCs in the SVZ can be targeted with a variety of pharmacotherapies. Thus, the SVZ can yield aggressive tumors but can be targeted via several strategies.

Dual role for DOCK7 in tangential migration of interneuron precursors in the postnatal forebrain

Throughout life, stem cells in the ventricular-subventricular zone generate neuroblasts that migrate via the rostral migratory stream (RMS) to the olfactory bulb, where they differentiate into local interneurons. Although progress has been made toward identifying extracellular factors that guide the migration of these cells, little is known about the intracellular mechanisms that govern the dynamic reshaping of the neuroblasts' morphology required for their migration along the RMS. In this study, we identify DOCK7, a member of the DOCK180-family, as a molecule essential for tangential neuroblast migration in the postnatal mouse forebrain. DOCK7 regulates the migration of these cells by controlling both leading process (LP) extension and somal translocation via distinct pathways. It controls LP stability/growth via a Rac-dependent pathway, likely by modulating microtubule networks while also regulating F-actin remodeling at the cell rear to promote somal translocation via a previously unrecognized myosin phosphatase-RhoA-interacting protein-dependent pathway. The coordinated action of both pathways is required to ensure efficient neuroblast migration along the RMS.

Nestin regulates neural stem cell migration via controlling the cell contractility

Neural stem cells (NSCs) migration is essential for neurogenesis and neuroregeneration after brain injury. Nestin, a widely used marker of NSCs, is expressed abundantly in several cancers, where it may correlate with tumor migration and invasion. However, it is not yet known whether nestin participates in NSC migration. Here, we show that nestin down-regulation significantly inhibits the migration and contraction of murine neural stem cells, but does not obviously influence the proliferation, filamentous actin (F-actin) content, distribution or focal adhesion assembly of these cells. Mechanistically, nestin knockdown was found to affect the phosphorylation state of myosin regulatory light chain (MRLC) and regulate the activity of myosin light chain kinase (MLCK). Co-immunoprecipitation experiments showed that it interacts with MLCK and MRLC. Together, our results indicate that nestin may increase NSC motility via elevating MLCK activity through direct binding and provide new insight into the roles of nestin in NSC migration and repair.

Application of an RNA amplification method for reliable single-cell transcriptome analysis

Diverse cell types have unique transcriptional signatures that are best interrogated at single-cell resolution. Here we describe a novel RNA amplification approach that allows for high fidelity gene profiling of individual cells. This technique significantly diminishes the problem of 3' bias, enabling detection of all regions of transcripts, including the recognition of mRNA with short or completely absent poly(A) tails, identification of noncoding RNAs, and discovery of the full array of splice isoforms from any given gene product. We assess this technique using statistical and bioinformatics analyses of microarray data to establish the limitations of the method. To demonstrate applicability, we profiled individual cells isolated from the mouse subventricular zone (SVZ)-a well-characterized, discrete yet highly heterogeneous neural structure involved in persistent neurogenesis. Importantly, this method revealed multiple splice variants of key germinal zone gene products within individual cells, as well as an unexpected coexpression of several mRNAs considered markers of distinct and separate SVZ cell types. These findings were independently confirmed using RNA-fluorescence in situ hybridization (RNA-FISH), contributing to the utility of this new technology that offers genomic and transcriptomic analysis of small numbers of dynamic and clinically relevant cells.

Protein tyrosine phosphatase-PEST and β8 integrin regulate spatiotemporal patterns of RhoGDI1 activation in migrating cells

Directional cell motility is essential for normal development and physiology, although how motile cells spatiotemporally activate signaling events remains largely unknown. Here, we have characterized an adhesion and signaling unit comprised of protein tyrosine phosphatase (PTP)-PEST and the extracellular matrix (ECM) adhesion receptor β8 integrin that plays essential roles in directional cell motility. β8 integrin and PTP-PEST form protein complexes at the leading edge of migrating cells and balance patterns of Rac1 and Cdc42 signaling by controlling the subcellular localization and phosphorylation status of Rho GDP dissociation inhibitor 1 (RhoGDI1). Translocation of Src-phosphorylated RhoGDI1 to the cell's leading edge promotes local activation of Rac1 and Cdc42, whereas dephosphorylation of RhoGDI1 by integrin-bound PTP-PEST promotes RhoGDI1 release from the membrane and sequestration of inactive Rac1/Cdc42 in the cytoplasm. Collectively, these data reveal a finely tuned regulatory mechanism for controlling signaling events at the leading edge of directionally migrating cells.

Detection of mouse endogenous type B astrocytes migrating towards brain lesions

Neuroblasts represent the predominant migrating cell type in the adult mouse brain. There are, however, increasing evidences of migration of other neural precursors. This work aims at identifying in vivo endogenous early neural precursors, different from neuroblasts, able to migrate in response to brain injuries. The monoclonal antibody Nilo1, which unequivocally identifies type B astrocytes and embryonic radial glia, was coupled to magnetic glyconanoparticles (mGNPs). Here we show that Nilo1-mGNPs in combination with magnetic resonance imaging in living mice allowed the in vivo identification of endogenous type B astrocytes at their niche, as well as their migration to the lesion site in response to glioblastoma, demyelination, cryolesion or mechanical injuries. In addition, Nilo1(+) adult radial glia-like structures were identified at the lesion site a few hours after damage. For all damage models used, type B astrocyte migration was fast and orderly. Identification of Nilo1(+) cells surrounding an induced glioblastoma was also possible after intraperitoneal injection of the antibody. This opens up the possibility of an early identification of the initial damage site(s) after brain insults, by the migration of type B astrocytes.

GSK3β regulates oligodendrogenesis in the dorsal microdomain of the subventricular zone via Wnt-β-catenin signaling

Oligodendrocytes, the myelinating cells of the CNS, are derived postnatally from oligodendrocyte precursors (OPs) of the subventricular zone (SVZ). However, the mechanisms that regulate their generation from SVZ neural stem cells (NSC) are poorly understood. Here, we have examined the role of glycogen synthase kinase 3β (GSK3β), an effector of multiple converging signaling pathways in postnatal mice. The expression of GSK3β by rt-qPCR was most prominent in the SVZ and in the developing white matter, around the first 1–2 weeks of postnatal life, coinciding with the peak periods of OP differentiation. Intraventricular infusion of the GSK3β inhibitor ARA-014418 in mice aged postnatal day (P) 8–11 significantly increased generation of OPs in the dorsal microdomain of the SVZ, as shown by expression of cell specific markers using rt-qPCR and immunolabelling. Analysis of stage specific markers revealed that the augmentation of OPs occurred via increased specification from earlier SVZ cell types. These effects of GSK3β inhibition on the dorsal SVZ were largely attributable to stimulation of the canonical Wnt/β-catenin signaling pathway over other pathways. The results indicate GSK3β is a key endogenous factor for specifically regulating oligodendrogenesis from the dorsal SVZ microdomain under the control of Wnt-signaling.

Traumatic brain injury reveals novel cell lineage relationships within the subventricular zone

The acute response of the rodent subventricular zone (SVZ) to traumatic brain injury (TBI) involves a physical expansion through increased cell proliferation. However, the cellular underpinnings of these changes are not well understood. Our analyses have revealed that there are two distinct transit-amplifying cell populations that respond in opposite ways to injury. Mash1+ transit-amplifying cells are the primary SVZ cell type that is stimulated to divide following TBI. In contrast, the EGFR+ population, which has been considered to be a functionally equivalent progenitor population to Mash1+ cells in the uninjured brain, becomes significantly less proliferative after injury. Although normally quiescent GFAP+ stem cells are stimulated to divide in SVZ ablation models, we found that the GFAP+ stem cells do not divide more after TBI. We found, instead, that TBI results in increased numbers of GFAP+/EGFR+ stem cells via non-proliferative means-potentially through the dedifferentiation of progenitor cells. EGFR+ progenitors from injured brains only were competent to revert to a stem cell state following brief exposure to growth factors. Thus, our results demonstrate previously unknown changes in lineage relationships that differ from conventional models and likely reflect an adaptive response of the SVZ to maintain endogenous brain repair after TBI.

Radixin inhibition decreases adult neural progenitor cell migration and proliferation in vitro and in vivo

Neuronal progenitors capable of long distance migration are produced throughout life in the subventricular zone (SVZ). Migration from the SVZ is carried out along a well-defined pathway called the rostral migratory stream (RMS). Our recent finding of the specific expression of the cytoskeleton linker protein radixin in neuroblasts suggests a functional role for radixin in RMS migration. The ezrin-radixin-moesin (ERM) family of proteins is capable of regulating migration through interaction with the actin cytoskeleton and transmembrane proteins. The ERM proteins are differentially expressed in the RMS with radixin and moesin localized to neuroblasts, and ezrin expression confined to astrocytes of the glial tubes. Here, we inhibited radixin function using the quinocarmycin analog DX52-1 which resulted in reduced neuroblast migration in vitro, while glial migration remained unaltered. Furthermore, the morphology of neuroblasts was distorted resulting in a rounded shape with no or short polysialylated neural cell adhesion molecule positive processes. Intracerebroventricular infusion of the radixin inhibitor resulted in accumulation of neuroblasts in the anterior SVZ. Neuroblast chains were short and intermittently interrupted in the SVZ and considerably disorganized in the RMS. Moreover, we studied the proliferation activity in the RMS after radixin inhibition, since concentrated radixin expression has been demonstrated in the cleavage furrow of dividing cells, which indicates a role of radixin in cell division. Radixin inhibition decreased neuroblast proliferation, whereas the proliferation of other cells in the RMS was not affected. Our results demonstrate a significant role for radixin in neuroblast proliferation and migration.

SCIRR39 promotes neurite extension via RhoA in NGF-induced PC12 cells

SCIRR39 is an identified upregulated gene in rat primary neuron injury and/or regeneration process with roles largely unexplored. Using real-time quantitative PCR, Western blotting and immunofluorescence, SCIRR39 expression was detected in normal PC12 cells and upregulated in differentiated cells. The results of cell proliferation by Cell Counting Kit and cell cycle by flow cytometry indicated that SCIRR39 inhibited cell proliferation and induced the decrease in S phase. Importantly, immunofluorescent and RhoA pull-down assays showed that SCIRR39 strongly affected the neurite extension of NGF-treated PC12 cells through a RhoA-dependent mechanism, but the truncated mutants of SCIRR39 containing a truncation from 141AA to 211AA or from 397AA to 424AA failed to mock the SCIRR39 effect on neurite extension. Moreover, change of SCIRR39 expression in NGF-treated PC12 cells regulated the expression and phosphorylation of Fyn, a regulator of RhoA activity, but not the expression of ROCK II protein. Finally, immunofluorescence and RhoA pull-down assays revealed that obvious inhibition of neurite extension by SCIRR39 shRNA was reversed by RhoA inhibitor C3-transferase. Our results indicated that SCIRR39 increased the neurite extension in NGF-treated PC12 cells via RhoA, suggesting that SCIRR39 contributes to the regeneration of neuron injury by specifically altering the differentiation program.

The extracellular matrix glycoprotein tenascin-R affects adult but not developmental neurogenesis in the olfactory bulb

Neuronal precursors produced in the subventricular zone throughout an animal's life migrate tangentially along the rostral migratory stream and, once in the olfactory bulb (OB), turn to migrate radially to the bulbar layers, where they differentiate into interneurons. Despite extensive investigations, it has remained largely unknown whether the same molecular mechanisms control OB neurogenesis during early postnatal development and in adulthood. In this study, we show that the extracellular matrix glycoprotein tenascin-R (TNR) is produced in the granule cell layer of the OB and that its expression increases during postnatal development. Time-lapse video imaging and morphological analyses revealed that a lack of TNR decreases the radial migration of neuronal precursors in the adult, but not in the developing OB. A lack of TNR also reduces spine development of newborn neurons in adult mice. To understand the functional consequences of a lack of TNR, we performed electrophysiological and behavioral studies on young and adult mice. Electrophysiological recordings showed that mitral cells, the target cells of newly generated interneurons, receive reduced spontaneous and evoked inhibitory activity in adult, but not young, TNR knock-out mice. Moreover, the synchronized activity of mitral cells was decreased in the OB of adult TNR knock-out mice. Behavioral studies revealed that the lower numbers of newborn interneurons in the adult OB induce alterations in short-term odor memory. Our results indicate that TNR modulates adult but not developmental neurogenesis in the OB and also highlight that the regulation of OB neurogenesis can vary during an animal's lifetime.

Intravital confocal and two-photon imaging of dual-color cells and extracellular matrix mimics

We report our efforts in identifying optimal scanning laser microscope parameters to study cells in three-dimensional culture. For this purpose we studied contrast of extracellular matrix (ECM) mimics, as well as signal attenuation, and bleaching of red and green fluorescent protein labeled cells. Confocal backscattering, second harmonic generation (SHG), and autofluorescence were sources of contrast in ECM mimics. All common ECM mimics exhibit contrast observable with confocal reflectance microscopy. SHG imaging on collagen I based hydrogels provides high contrast and good optical penetration depth. Agarose is a useful embedding medium because it allows for large optical penetration and exhibits minimal autofluorescence. We labeled breast cancer cells' outline with DsRed2 and nucleus with enhanced green fluorescent protein (eGFP). We observed significant difference both for the bleaching rates of eGFP and DsRed2 where bleaching is strongest during two-photon excitation (TPE) and smallest during confocal imaging. But for eGFP the bleaching rate difference is smaller than for DsRed2. After a few hundred microns depth in a collagen I hydrogel, TPE fluorescence of DsRed2 becomes twice as strong compared to confocal imaging. In fibrin and agarose gels, the imaging depth will need to be beyond 1 mm to notice a TPE advantage.

Dynamic changes in the transcriptional profile of subventricular zone-derived postnatally born neuroblasts

The subventricular zone (SVZ) of the lateral ventricles is a major neurogenic region in the postnatal mammalian brain. Thousands of neuroblasts are generated daily throughout the life of an animal. Newly born neuroblasts migrate via the rostral migratory stream (RMS) into the olfactory bulb where they mature into distinct neuronal subtypes. Neuroblasts exiting the SVZ retain the ability to proliferate, however, proliferation declines in the course of migration to the olfactory bulb. While migrating in the RMS, neuroblasts receive a plethora of stimuli that modify transcription according to the local microenvironment, and eventually modulate neuroblast migration. In the target area, the olfactory bulb, neuroblasts develop into mature neurons. In this review, we discuss dynamic changes of the transcriptome that occur during the "lifetime" of a neuroblast, thereby governing the activation or inhibition of distinct genes/pathways that are responsible for proliferation, migration and differentiation.

3-dimensional examination of the adult mouse subventricular zone reveals lineage-specific microdomains

Recent studies suggest that the subventricular zone (SVZ) of the lateral ventricle is populated by heterogeneous populations of stem and progenitor cells that, depending on their exact location, are biased to acquire specific neuronal fates. This newly described heterogeneity of SVZ stem and progenitor cells underlines the necessity to develop methods for the accurate quantification of SVZ stem and progenitor subpopulations. In this study, we provide 3-dimensional topographical maps of slow cycling “stem” cells and progenitors based on their unique cell cycle properties. These maps revealed that both cell populations are present throughout the lateral ventricle wall as well as in discrete regions of the dorsal wall. Immunodetection of transcription factors expressed in defined progenitor populations further reveals that divergent lineages have clear regional enrichments in the rostro-caudal as well as in the dorso-ventral span of the lateral ventricle. Thus, progenitors expressing Tbr2 and Dlx2 were confined to dorsal and dorso-lateral regions of the lateral ventricle, respectively, while Mash1+ progenitors were more homogeneously distributed. All cell populations were enriched in the rostral-most region of the lateral ventricle. This diversity and uneven distribution greatly impede the accurate quantification of SVZ progenitor populations. This is illustrated by measuring the coefficient of error of estimates obtained by using increasing section sampling interval. Based on our empirical data, we provide such estimates for all progenitor populations investigated in this study. These can be used in future studies as guidelines to judge if the precision obtained with a sampling scheme is sufficient to detect statistically significant differences between experimental groups if a biological effect is present. Altogether, our study underlines the need to consider the SVZ of the lateral ventricle as a complex 3D structure and define methods to accurately assess neural stem cells or progenitor diversity and population sizes in physiological or experimental paradigms.

The path from the choroid plexus to the subventricular zone: go with the flow!

In adult mammals, under physiological conditions, neurogenesis, the process of generating new functional neurons from precursor cells, occurs mainly in two brain areas: the subgranular zone in the dentate gyrus of the hippocampus, and the subventricular zone (SVZ) lining the walls of the brain lateral ventricles. Taking into account the location of the SVZ and the cytoarchitecture of this periventricular neural progenitor cell niche, namely the fact that the slow dividing primary progenitor cells (type B cells) of the SVZ extend an apical primary cilium toward the brain ventricular space which is filled with cerebrospinal fluid (CSF), it becomes likely that the composition of the CSF can modulate both self-renewal, proliferation and differentiation of SVZ neural stem cells. The major site of CSF synthesis is the choroid plexus (CP); quite surprisingly, however, it is still largely unknown the contribution of molecules specifically secreted by the adult CP as modulators of the SVZ adult neurogenesis. This is even more relevant in light of recent evidence showing the ability of the CP to adapt its transcriptome and secretome to various physiologic and pathologic stimuli. By giving particular emphasizes to growth factors and axonal guidance molecules we will illustrate how CP-born molecules might play an important role in the SVZ niche cell population dynamics.

Pten deletion causes mTorc1-dependent ectopic neuroblast differentiation without causing uniform migration defects

Neuronal precursors, generated throughout life in the subventricular zone, migrate through the rostral migratory stream to the olfactory bulb where they differentiate into interneurons. We found that the PI3K-Akt-mTorc1 pathway is selectively inactivated in migrating neuroblasts in the subventricular zone and rostral migratory stream, and activated when these cells reach the olfactory bulb. Postnatal deletion of Pten caused aberrant activation of the PI3K-Akt-mTorc1 pathway and an enlarged subventricular zone and rostral migratory stream. This expansion was caused by premature termination of migration and differentiation of neuroblasts and was rescued by inhibition of mTorc1. This phenotype is reminiscent of lamination defects caused by Pten deletion in developing brain that were previously described as defective migration. However, live imaging in acute slices showed that Pten deletion did not cause a uniform defect in the mechanics of directional neuroblast migration. Instead, a subpopulation of Pten-null neuroblasts showed minimal movement and altered morphology associated with differentiation, whereas the remainder showed unimpeded directional migration towards the olfactory bulb. Therefore, migration defects of Pten-null neurons might be secondary to ectopic differentiation.

Regional differences in human ependymal and subventricular zone cytoarchitecture are unchanged in neuropsychiatric disease

Much work has focused on the possible contribution of adult hippocampal neurogenesis to neuropsychiatric diseases. The hippocampal subgranular zone and the other stem cell-containing neurogenic niche, the subventricular zone (SVZ), share several cytological features and are regulated by some of the same molecular mechanisms. However, very little is known about the SVZ in neuropsychiatric disorders. This is important since it surrounds the lateral ventricles and in schizophrenia ventricular enlargement frequently follows forebrain nuclei shrinkage. Also, adult neurogenesis has been implicated in pharmacotherapy for affective disorders and many of the molecules associated with neuropsychiatric disorders affect SVZ biology. To assess the neurogenic niche, we examined material from 60 humans (Stanley Collection) and characterized the cytoarchitecture of the SVZ and ependymal layer in age-, sex- and post mortem interval-matched controls, and patients diagnosed with schizophrenia, bipolar illness, and depression (n = 15 each). There is a paucity of post mortem brains available for study in these diseases, so to maximize the number of possible parameters examined here, we quantified individual sections rather than a large series. Previous work showed that multiple sclerosis is associated with increased width of the hypocellular gap, a cell-sparse region that typifies the human SVZ. Statistically there were no differences between disease groups and controls in the width of the hypocellular gap or in the density of cells in the hypocellular gap. Because ventricular enlargement in schizophrenia may disrupt ependymal cells, we quantified them, but observed no difference between diagnostic groups and controls. There are significant differences in the prevalence of neuropsychiatric illness between the sexes. Therefore, we looked for male versus female differences, but did not observe any in the parameters quantified. We next turned to a finer spatial resolution and asked if there were differences amongst the disease groups in dorsal ventral subdivisions of the SVZ. Similar to when we treated the SVZ as a whole, we did not find such differences. However, compared to the dorsal SVZ, the ventral SVZ had a wider hypocellular gap and more ependymal cells in all four groups. In contrast, cell density was similar in dorsal ventral subregions of the SVZ hypocellular gap. These results show that though there are regional differences in the SVZ in humans, neuropsychiatric disorders do not seem to alter several fundamental histological features of this adult neurogenic zone.

Inflammatory regulators of redirected neural migration in the injured brain

Brain injury following stroke or trauma induces the migration of neuroblasts derived from subventricular zone neural precursor cells (NPCs) towards the damaged tissue, where they then have the potential to contribute to repair. Enhancing the recruitment of new cells thus presents an enticing prospect for the development of new therapeutic approaches to treat brain injury; to this end, an understanding of the factors regulating this process is required. During the neuroinflammatory response to ischemic and traumatic brain injuries, a plethora of pro- and anti-inflammatory cytokines, chemokines and growth factors are released in the damaged tissue, and recent work indicates that a variety of these are able to influence injury-induced migration. In this review, we will discuss the contribution of specific chemokines and growth factors towards stimulating NPC migration in the injured brain.

Neural stem cell depletion and CNS developmental defects after enteroviral infection

Coxsackieviruses are significant human pathogens causing myocarditis, meningitis, and encephalitis. We previously demonstrated the ability of coxsackievirus B3 (CVB3) to persist within the neonatal central nervous system (CNS) and to target neural stem cells. Given that CVB3 is a cytolytic virus and may therefore damage target cells, we characterized the potential reduction in neurogenesis within the developing brain and the subsequent developmental defects that occurred after the loss of these essential neural stem cells. Neonatal mice were inoculated with a recombinant CVB3 expressing eGFP (eGFP-CVB3), and alterations in neurogenesis and brain development were evaluated over time. We observed a reduction in proliferating cells in CNS neurogenic regions simultaneously with the presence of nestin(+) cells undergoing apoptosis. The size of the brain appeared smaller by histology, and a permanent decrease in brain wet weight was observed after eGFP-CVB3 infection. We also observed an inverse relationship between the amount of virus material and brain wet weight up to day 30 postinfection. In addition, signs of astrogliosis and a compaction of the cortical layers were observed at 90 days postinfection. Intriguingly, partial brain wet weight recovery was observed in mice treated with the antiviral drug ribavirin during the persistent stage of infection. Hence, long-term neurological sequelae might be expected after neonatal enteroviral infections, yet antiviral treatment initiated long after the end of acute infection might limit virus-mediated neuropathology.

Multipotent progenitor cells derived from adult peripheral blood of swine have high neurogenic potential in vitro

Peripheral blood-derived multipotent adult progenitor cells (PBD-MAPCs) are a novel population of stem cells, isolated from venous blood of green fluorescent protein transgenic swine, which proliferate as multicellular non-adherent spheroids. Using a simple differentiation protocol, a large proportion of these cells developed one of five distinct neural cell phenotypes, indicating that these primordial cells have high neurogenic potential. Cells exhibiting neural morphologies developed within 48 h of exposure to differentiation conditions, increased in percentage over 2 weeks, and stably maintained the neural phenotype for three additional weeks in the absence of neurogenic signaling molecules. Cells exhibited dynamic neural-like behaviors including extension and retraction of processes with growth cone-like structures rich in filamentous actin, cell migration following a leading process, and various cell-cell interactions. Differentiated cells expressed neural markers, NeuN, β-tubulin III and synaptic proteins, and progenitor cells expressed the stem cell markers nestin and NANOG. Neurally differentiated PBD-MAPCs exhibited voltage-dependent inward and outward currents and expressed voltage-gated sodium and potassium channels, suggestive of neural-like membrane properties. PBD-MAPCs expressed early neural markers and developed neural phenotypes when provided with an extracellular matrix of laminin without the addition of cytokines or growth factors, suggesting that these multipotent cells may be primed for neural differentiation. PBD-MAPCs provide a model for understanding the mechanisms of neural differentiation from non-neural sources of adult stem cells. A similar population of cells, from humans or xenogeneic sources, may offer the potential of an accessible, renewable and non-tumorigenic source of stem cells for treating neural disorders.

Cross-disorder analysis of bipolar risk genes: further evidence of DGKH as a risk gene for bipolar disorder, but also unipolar depression and adult ADHD

Recently, several genome-wide association studies (GWAS) on bipolar disorder (BPD) suggested novel risk genes. However, only few of them were followed up and further, the specificity of these genes is even more elusive. To address these issues, we genotyped SNPs in ANK3, CACNA1C, CMTM8, DGKH, EGFR, and NPAS3, which were significantly associated with BPD in previous GWAS, in a sample of 380 BPD patients. Replicated SNPs were then followed up in patients suffering from unipolar depression (UPD; n=387) or adult attention-deficit/hyperactivity disorder (aADHD; n=535). While we could not confirm an association of ANK3, CACNA1C, and EGFR with BPD, 10 SNPs in DGKH, CMTM8, and NPAS3 were nominally associated with disease, with two DGKH markers surviving correction for multiple testing. When these were followed up in UPD and aADHD, seven DGKH SNPs were also associated with UPD, while one SNP each in NPAS3 and CMTM8 and four in DGKH were linked to aADHD. Furthermore, a DGKH haplotype consisting of rs994856/rs9525580/rs9525584 GAT was associated with all disorders tested, while the complementary AGC haplotype was protective. The corresponding haploblock spans a 27-kb region covering exons coding for amino acids 65-243, and thus might include functional variants yet to be identified. We demonstrate an association of DGKH with BPD, UPD, and aADHD by applying a two-stage design. These disorders share the feature of mood instability, so that this phenotype might be associated with genetic variation in DGKH.

Lake-front property: a unique germinal niche by the lateral ventricles of the adult brain

New neurons and glial cells are generated in an extensive germinal niche adjacent to the walls of the lateral ventricles in the adult brain. The primary progenitors (B1 cells) have astroglial characteristics but retain important neuroepithelial properties. Recent work shows how B1 cells contact all major compartments of this niche. They share the "shoreline" on the ventricles with ependymal cells, forming a unique adult ventricular zone (VZ). In the subventricular zone (SVZ), B1 cells contact transit amplifying (type C) cells, chains of young neurons (A cells), and blood vessels. How signals from these compartments influence the behavior of B1 or C cells remains largely unknown, but recent work highlights growth factors, neurotransmitters, morphogens, and the extracellular matrix as key regulators of this niche. The integration of emerging molecular and anatomical clues forecasts an exciting new understanding of how the germ of youth is actively maintained in the adult brain.

Galectin-3 maintains cell motility from the subventricular zone to the olfactory bulb

The adult brain subventricular zone (SVZ) produces neuroblasts that migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB) in a specialized niche. Galectin-3 (Gal-3) regulates proliferation and migration in cancer and is expressed by activated macrophages after brain injury. The function of Gal-3 in the normal brain is unknown, but we serendipitously found that it was expressed by ependymal cells and SVZ astrocytes in uninjured mice. Ependymal cilia establish chemotactic gradients and astrocytes form glial tubes, which combine to aid neuroblast migration. Whole-mount preparations and electron microscopy revealed that both ependymal cilia and SVZ astrocytes were disrupted in Gal3(-/-) mice. Interestingly, far fewer new BrdU(+) neurons were found in the OB of Gal3(-/-) mice, than in wild-type mice 2 weeks after labeling. However, SVZ proliferation and cell death, as well as OB differentiation rates were unaltered. This suggested that decreased migration in vivo was sufficient to decrease the number of new OB neurons. Two-photon time-lapse microscopy in forebrain slices confirmed decreased migration; cells were slower and more exploratory in Gal3(-/-) mice. Gal-3 blocking antibodies decreased migration and dissociated neuroblast cell-cell contacts, whereas recombinant Gal-3 increased migration from explants. Finally, we showed that expression of phosphorylated epidermal growth factor receptor (EGFR) was increased in Gal3(-/-) mice. These results suggest that Gal-3 is important in SVZ neuroblast migration, possibly through an EGFR-based mechanism, and reveals a role for this lectin in the uninjured brain.

Cellular and molecular determinants of stroke-induced changes in subventricular zone cell migration

A remarkable aspect of adult neurogenesis is that the tight regulation of subventricular zone (SVZ) neuroblast migration is altered after ischemic stroke and newborn neurons emigrate towards the injury. This phenomenon is an essential component of endogenous repair and also serves to illuminate normal mechanisms and rules that govern SVZ migration. Stroke causes inflammation that leads to cytokine and chemokine release, and SVZ neuroblasts that express their receptors are recruited. Metalloproteinases create pathways and new blood vessels provide a scaffold to facilitate neuroblast migration between the SVZ and the infarct. Most experiments have studied the peri-lesion parenchyma and relatively little is known about SVZ remodeling after stroke. Migration in the SVZ is tightly regulated by cellular interactions and molecular signaling; how are these altered after stroke to allow emigration? Do ependymal cells contribute to this process, given their reported neurogenic potential? How does stroke affect ependymal cell regulation of cerebrospinal fluid flow? Given the heterogeneity of SVZ progenitors, do all types of neuroblasts migrate out, or is this confined to specific subtypes of cells? We discuss these and other questions in our review and propose experiments to address them.

Subventricular zone cell migration: lessons from quantitative two-photon microscopy

Neuroblasts born in the adult subventricular zone (SVZ) migrate long distances in the rostral migratory stream (RMS) to the olfactory bulbs where they integrate into circuitry as functional interneurons. As very little was known about the dynamic parameters of SVZ neuroblast migration, we used two-photon time-lapse microscopy to analyze migration in acute slices. This involved analyzing 3D stacks of images over time and uncovered several novel aspects of SVZ migration: chains remain stable, cells can be immotile for extensive periods, morphology does not necessarily correlate with motility, neuroblasts exhibit local exploratory motility, dorsoventral migration occurs throughout the striatal SVZ, and neuroblasts turn at distinctive angles. We investigated these novel findings in the SVZ and RMS from the population to the single cell level. In this review we also discuss some technical considerations when setting up a two-photon microscope imaging system. Throughout the review we identify several unsolved questions about SVZ neuroblast migration that might be addressed with current or emerging techniques.

Nestin reporter transgene labels multiple central nervous system precursor cells

Embryonic neuroepithelia and adult subventricular zone (SVZ) stem and progenitor cells express nestin. We characterized a transgenic line that expresses enhanced green fluorescent protein (eGFP) specified to neural tissue by the second intronic enhancer of the nestin promoter that had several novel features. During embryogenesis, the dorsal telencephalon contained many and the ventral telencephalon few eGFP+ cells. eGFP+ cells were found in postnatal and adult neurogenic regions. eGFP+ cells in the SVZ expressed multiple phenotype markers, glial fibrillary acidic protein, Dlx, and neuroblast-specific molecules suggesting the transgene is expressed through the lineage. eGFP+ cell numbers increased in the SVZ after cortical injury, suggesting this line will be useful in probing postinjury neurogenesis. In non-neurogenic regions, eGFP was strongly expressed in oligodendrocyte progenitors, but not in astrocytes, even when they were reactive. This eGFP+ mouse will facilitate studies of proliferative neuroepithelia and adult neurogenesis, as well as of parenchymal oligodendrocytes.

Rostral migratory stream neuroblasts turn and change directions in stereotypic patterns

Neuroblasts generated in the adult subventricular zone (SVZ) migrate through the rostral migratory stream (RMS) to the olfactory bulb (OB). Previous work uncovered motility ranging from straight to complex, but it was unclear if directional changes were stochastic or exhibited stereotypical patterns. Here, we provide the first in-depth two-photon time-lapse microscopy study of morphological and dynamic features that accompany turning and direction reversals in the RMS. We identified three specific kinds of turning (30-90 degrees): bending of the leading process proximal to the cell body (P-bending 47% of cases), bending of the distal leading process (D-bending 30%) or branching of the leading process or lamellipodium (23%). Bending and branching angles were remarkably constrained and were significantly different from one another. Cells reversed direction (> 90 degrees) through D-bendings (54%), branching (11%) or de novo growth of processes from the soma (23%), but not P-bending. Direction reversal was often composed of several iterations of D-bending or branching as opposed to novel modalities. Individual neuroblasts could turn or change direction in multiple patterns suggesting that the patterns are not specific for different lineages. These findings show that neuroblasts in the RMS use a limited number of distinct and constrained modalities to turn or reverse direction.

Imaging and recording subventricular zone progenitor cells in live tissue of postnatal mice

The subventricular zone (SVZ) is one of two regions where neurogenesis persists in the postnatal brain. The SVZ, located along the lateral ventricle, is the largest neurogenic zone in the brain that contains multiple cell populations including astrocyte-like cells and neuroblasts. Neuroblasts migrate in chains to the olfactory bulb where they differentiate into interneurons. Here, we discuss the experimental approaches to record the electrophysiology of these cells and image their migration and calcium activity in acute slices. Although these techniques were in place for studying glial cells and neurons in mature networks, the SVZ raises new challenges due to the unique properties of SVZ cells, the cellular diversity, and the architecture of the region. We emphasize different methods, such as the use of transgenic mice and in vivo electroporation that permit identification of the different SVZ cell populations for patch clamp recording or imaging. Electroporation also permits genetic labeling of cells using fluorescent reporter mice and modification of the system using either RNA interference technology or floxed mice. In this review, we aim to provide conceptual and technical details of the approaches to perform electrophysiological and imaging studies of SVZ cells.

Dose-dependent effect of EGF on migration and differentiation of adult subventricular zone astrocytes

Adult neural stem cells (NSCs) are located in the subventricular zone (SVZ), a specialized brain niche located on the walls of the lateral ventricle. Under physiological conditions, NSCs generate a large number of young neurons and some oligodendrocytes, however the mechanisms controlling cell proliferation and migration are unclear. In vitro, epidermal growth factor (EGF) signaling has been shown to be an important mediator of cell proliferation and migration in the adult brain; however, the primary SVZ progenitors that respond to EGF are not well known. In this study, we isolated SVZ type-B astrocytes and cultured them under different EGF concentrations. We found a dose-dependent effect of EGF on proliferation rates and migration of SVZ type-B astrocytes. We found that GFAP+ type-B astrocytes gave rise to highly migratory and proliferating cells that expressed Olig2 and NG2. After EGF withdrawal, a significant number of EGF-stimulated cells differentiated into S100beta+/O4+ oligodendrocytes. This study provides new insights about the production of oligodendrocytes derived from the astrocyte NSCs residing in the adult SVZ. To be able to manipulate the endogenous adult progenitors, it is crucial to identify and isolate the responding primary precursors and determine the extracellular signals that regulate their cell division, migration, and fate.

Characterization of novel monoclonal antibodies able to identify neurogenic niches and arrest neurosphere proliferation and differentiation

Two monoclonal antibodies (Nilo1 and Nilo2) were generated after immunization of hamsters with E13.5 olfactory bulb-derived mouse neurospheres. They are highly specific for neural stem and early progenitor cell surface antigens. Nilo positive cells present in the adult mouse subventricular zone (SVZ) were able to initiate primary neural stem cell cultures. Moreover, these antibodies added to neurosphere cultures induced proliferation arrest and interfered with their differentiation. In the lateral ventricles of adult mice, Nilo1 stained a cell subpopulation lining the ventricle and cells located in the SVZ, whereas Nilo2 stained a small population associated with the anterior horn of the SVZ at the beginning of the rostral migratory stream. Co-staining of Nilo1 or Nilo2 and neural markers demonstrated that Nilo1 identifies an early neural precursor subpopulation, whereas Nilo2 detects more differentiated neural progenitors. Thus, these antibodies identify distinct neurogenic populations within the SVZ of the lateral ventricle.

Chordin-induced lineage plasticity of adult SVZ neuroblasts after demyelination

The mechanisms that regulate the developmental potential of adult neural progenitor populations under physiological and pathological conditions remain poorly defined. Glutamic acid decarboxylase 65 (GAD65)- and Doublecortin (Dcx)-expressing cells constitute major progenitor populations in the adult mouse subventricular zone (SVZ). Under normal physiological conditions, SVZ-derived GAD65-positive and Dcx-positive cells expressed the transcription factor Pax6 and migrated along the rostral migratory stream to the olfactory bulb to generate interneurons. After lysolecithin-induced demyelination of corpus callosum, however, these cells altered their molecular and cellular properties and migratory path. Demyelination upregulated chordin in the SVZ, which redirected GAD65-positive and Dcx-positive progenitors from neuronal to glial fates, generating new oligodendrocytes in the corpus callosum. Our findings suggest that the lineage plasticity of SVZ progenitor cells could be a potential therapeutic strategy for diseased or injured brain.