EGFRs mediate chemotactic migration in the developing telencephalon

The Genetic Architecture of the Human Corpus Callosum and its Subregions

The corpus callosum (CC) is the largest set of white matter fibers connecting the two hemispheres of the brain. In humans, it is essential for coordinating sensorimotor responses, performing associative/executive functions, and representing information in multiple dimensions. Understanding which genetic variants underpin corpus callosum morphometry, and their shared influence on cortical structure and susceptibility to neuropsychiatric disorders, can provide molecular insights into the CC's role in mediating cortical development and its contribution to neuropsychiatric disease. To characterize the morphometry of the midsagittal corpus callosum, we developed a publicly available artificial intelligence based tool to extract, parcellate, and calculate its total and regional area and thickness. Using the UK Biobank (UKB) and the Adolescent Brain Cognitive Development study (ABCD), we extracted measures of midsagittal corpus callosum morphometry and performed a genome-wide association study (GWAS) meta-analysis of European participants (combined N = 46,685). We then examined evidence for generalization to the non-European participants of the UKB and ABCD cohorts (combined N = 7,040). Post-GWAS analyses implicate prenatal intracellular organization and cell growth patterns, and high heritability in regions of open chromatin, suggesting transcriptional activity regulation in early development. Results suggest programmed cell death mediated by the immune system drives the thinning of the posterior body and isthmus. Global and local genetic overlap, along with causal genetic liability, between the corpus callosum, cerebral cortex, and neuropsychiatric disorders such as attention-deficit/hyperactivity and bipolar disorders were identified. These results provide insight into variability of corpus callosum development, its genetic influence on the cerebral cortex, and biological mechanisms related to neuropsychiatric dysfunction.

S100A10 promotes HCC development and progression via transfer in extracellular vesicles and regulating their protein cargos

OBJECTIVE

Growing evidence indicates that tumour cells exhibit characteristics similar to their lineage progenitor cells. We found that S100 calcium binding protein A10 (S100A10) exhibited an expression pattern similar to that of liver progenitor genes. However, the role of S100A10 in hepatocellular carcinoma (HCC) progression is unclear. Furthermore, extracellular vesicles (EVs) are critical mediators of tumourigenesis and metastasis, but the extracellular functions of S100A10, particularly those related to EVs (EV-S100A10), are unknown.

DESIGN

The functions and mechanisms of S100A10 and EV-S100A10 in HCC progression were investigated in vitro and in vivo. Neutralising antibody (NA) to S100A10 was used to evaluate the significance of EV-S100A10.

RESULTS

Functionally, S100A10 promoted HCC initiation, self-renewal, chemoresistance and metastasis in vitro and in vivo. Of significance, we found that S100A10 was secreted by HCC cells into EVs both in vitro and in the plasma of patients with HCC. S100A10-enriched EVs enhanced the stemness and metastatic ability of HCC cells, upregulated epidermal growth factor receptor (EGFR), AKT and ERK signalling, and promoted epithelial-mesenchymal transition. EV-S100A10 also functioned as a chemoattractant in HCC cell motility. Of significance, S100A10 governed the protein cargos in EVs and mediated the binding of MMP2, fibronectin and EGF to EV membranes through physical binding with integrin αⅤ. Importantly, blockage of EV-S100A10 with S100A10-NA significantly abrogated these enhancing effects.

CONCLUSION

Altogether, our results uncovered that S100A10 promotes HCC progression significantly via its transfer in EVs and regulating the protein cargoes of EVs. EV-S100A10 may be a potential therapeutic target and biomarker for HCC progression.

Scientific Validation of Human Neurosphere Assays for Developmental Neurotoxicity Evaluation

There is a call for a paradigm shift in developmental neurotoxicity (DNT) evaluation, which demands the implementation of faster, more cost-efficient, and human-relevant test systems than current in vivo guideline studies. Under the umbrella of the Organisation for Economic Co-operation and Development (OECD), a guidance document is currently being prepared that instructs on the regulatory use of a DNT in vitro battery (DNT IVB) for fit-for-purpose applications. One crucial issue for OECD application of methods is validation, which for new approach methods (NAMs) requires novel approaches. Here, mechanistic information previously identified in vivo, as well as reported neurodevelopmental adversities in response to disturbances on the cellular and tissue level, are of central importance. In this study, we scientifically validate the Neurosphere Assay, which is based on human primary neural progenitor cells (hNPCs) and an integral part of the DNT IVB. It assesses neurodevelopmental key events (KEs) like NPC proliferation (NPC1ab), radial glia cell migration (NPC2a), neuronal differentiation (NPC3), neurite outgrowth (NPC4), oligodendrocyte differentiation (NPC5), and thyroid hormone-dependent oligodendrocyte maturation (NPC6). In addition, we extend our work from the hNPCs to human induced pluripotent stem cell-derived NPCs (hiNPCs) for the NPC proliferation (iNPC1ab) and radial glia assays (iNPC2a). The validation process we report for the endpoints studied with the Neurosphere Assays is based on 1) describing the relevance of the respective endpoints for brain development, 2) the confirmation of the cell type-specific morphologies observed in vitro, 3) expressions of cell type-specific markers consistent with those morphologies, 4) appropriate anticipated responses to physiological pertinent signaling stimuli and 5) alterations in specific in vitro endpoints upon challenges with confirmed DNT compounds. With these strong mechanistic underpinnings, we posit that the Neurosphere Assay as an integral part of the DNT in vitro screening battery is well poised for DNT evaluation for regulatory purposes.

Single-cell analysis reveals dynamic changes of neural cells in developing human spinal cord

During central nervous system development, neurogenesis and gliogenesis occur in an orderly manner to create precise neural circuitry. However, no systematic dataset of neural lineage development that covers both neurogenesis and gliogenesis for the human spinal cord is available. We here perform single-cell RNA sequencing of human spinal cord cells during embryonic and fetal stages that cover neuron generation as well as astrocytes and oligodendrocyte differentiation. We also map the timeline of sensory neurogenesis and gliogenesis in the spinal cord. We further identify a group of EGFR-expressing transitional glial cells with radial morphology at the onset of gliogenesis, which progressively acquires differentiated glial cell characteristics. These EGFR-expressing transitional glial cells exhibited a unique position-specific feature during spinal cord development. Cell crosstalk analysis using CellPhoneDB indicated that EGFR glial cells can persistently interact with other neural cells during development through Delta-Notch and EGFR signaling. Together, our results reveal stage-specific profiles and dynamics of neural cells during human spinal cord development.

The Role of Astrocytes in the Development of the Cerebellum

Astrocytes, initially described as merely support cells, are now known as a heterogeneous population of cells actively involved in a variety of biological functions such as: neuronal migration and differentiation; regulation of cerebral blood flow; metabolic control of extracellular potassium concentration; and modulation of synapse formation and elimination; among others. Cerebellar glial cells have been shown to play a significant role in proliferation, differentiation, migration, and synaptogenesis. However, less evidence is available about the role of neuron-astrocyte interactions during cerebellar development and their impact on diseases of the cerebellum. In this review, we will focus on the mechanisms underlying cellular interactions, specifically neuron-astrocyte interactions, during cerebellar development, function, and disease. We will discuss how cerebellar glia, astrocytes, and Bergmann glia play a fundamental role in several steps of cerebellar development, such as granule cell migration, axonal growth, neuronal differentiation, and synapse formation, and in diseases associated with the cerebellum. We will focus on how astrocytes and thyroid hormones impact cerebellar development. Furthermore, we will provide evidence of how growth factors secreted by glial cells, such as epidermal growth factor and transforming growth factors, control cerebellar organogenesis. Finally, we will argue that glia are a key mediator of cerebellar development and that identification of molecules and pathways involved in neuron-glia interactions may contribute to a better understanding of cerebellar development and associated disorders.

Essential oil extracted from erythrina corallodendron L. leaves inhibits the proliferation, migration, and invasion of breast cancer cells

Erythrina corallodendron L., a kind of landscape tree, has long been used as a traditional medicine. In this study, the composition of essential oil extracted from the leaves was analysed by GC-MS (gas chromatograph-mass spectrometer), with linalool identified as the main compound. Its cytotoxicity against MDA-MB-231, MCF-7 and HMLE cells was examined by MTT and cloning assays. Transwell and wound-healing assays were used to examine the inhibition of migration and invasion. Western blot, qRT-PCR and immunofluorescence staining were used to measure the mRNA and protein expression of factors related to EMT (snail, slug, E-cadherin, N-cadherin and vimentin). The essential oil of Erythrina corallodendron leaves was found to inhibit the proliferation, migration and invasion of breast cancer cells in a dose-dependent manner. The findings of this study suggest that the essential oil of E. corallodendron leaves may merit further investigation as a potential clinical or adjuvant drug for treating breast cancer migration and invasion.

Hnrnpab regulates neural cell motility through transcription of Eps8

Cell migration requires a complicated network of structural and regulatory proteins. Changes in cellular motility can impact migration as a result of cell-type or developmental stage regulated expression of critical motility genes. Hnrnpab is a conserved RNA-binding protein found as two isoforms produced by alternative splicing. Its expression is enriched in the subventricular zone (SVZ) and the rostral migratory stream within the brain, suggesting possible support of the migration of neural progenitor cells in this region. Here we show that the migration of cells from the SVZ of developing Hnrnpab^-/- mouse brains is impaired. An RNA-seq analysis to identify Hnrnpab-dependent cell motility genes led us to Eps8, and in agreement with the change in cell motility, we show that Eps8 is decreased in Hnrnpab^-/- SVZ tissue. We scrutinized the motility of Hnrnpab^-/- cells and confirmed that the decreases in both cell motility and Eps8 are restored by ectopically coexpressing both alternatively spliced Hnrnpab isoforms, therefore these variants are surprisingly nonredundant for cell motility. Our results support a model where both Hnrnpab isoforms work in concert to regulate Eps8 transcription in the mouse SVZ to promote the normal migration of neural cells during CNS development.

MicroRNA-129-5p is regulated by choline availability and controls EGF receptor synthesis and neurogenesis in the cerebral cortex

Choline availability modulates neurogenesis and cerebral cortex development through the regulation of neural progenitor cell (NPC) proliferative and differentiation capacity. In this study, we demonstrated that cortical NPC self-renewal is controlled by choline via the expression of a microRNA (miR-129-5p), whose role in the developing brain has not been examined, and which, in turn, inhibits synthesis of the epidermal growth factor receptor (EGFR) protein. Specifically, we found that low choline (LC) availability led to the upregulation of miR-129-5p expression in cortical NPCs in vitro and in vivo, causing the downregulation of EGFR and thereby disrupting NPC self-renewal and cortical neurogenesis. Furthermore, in response to LC availability, methylation potential (the S-adenosylmethionine: S-adenosylhomocysteine ratio) in the developing brain was reduced. Restoring methylation potential in LC cortical NPCs led to the re-establishment of normal miR-129-5p expression. We concluded that inhibiting miR-129-5p function and restoring EGFR protein levels in vivo is sufficient to reverse LC-induced defects in cortical NPC self-renewal. For the first time, to our knowledge, we have identified the molecular links that explain how a change in the availability of the diet metabolite choline impacts the essential cellular processes underlying brain development.-Trujillo-Gonzalez, I., Wang, Y., Friday, W. B., Vickers, K. C., Toth, C. L., Molina-Torres, L., Surzenko, N., Zeisel, S. H. MicroRNA-129-5p is regulated by choline availability and controls EGF receptor synthesis and neurogenesis in the cerebral cortex.

Crosstalk between receptor tyrosine kinases (RTKs) and G protein-coupled receptors (GPCR) in the brain: Focus on heteroreceptor complexes and related functional neurotrophic effects

Neuronal events are regulated by the integration of several complex signaling networks in which G protein-coupled receptors (GPCRs) and receptor tyrosine kinases (RTKs) are considered key players of an intense bidirectional cross-communication in the cell, generating signaling mechanisms that, at the same time, connect and diversify the traditional signal transduction pathways activated by the single receptor. For this receptor-receptor crosstalk, the two classes of receptors form heteroreceptor complexes resulting in RTKs transactivation and in growth-promoting signals. In this review, we describe heteroreceptor complexes between GPCR and RTKs in the central nervous system (CNS) and their functional effects in controlling a variety of neuronal effects, ranging from development, proliferation, differentiation and migration, to survival, repair, synaptic transmission and plasticity. In this interaction, RTKs can also recruit components of the G protein signaling cascade, creating a bidirectional intricate interplay that provides complex control over multiple cellular events. These heteroreceptor complexes, by the integration of different signals, have recently attracted a growing interest as novel molecular target for depressive disorders. This article is part of the Special Issue entitled 'Receptor heteromers and their allosteric receptor-receptor interactions'.

Astragaloside VI Promotes Neural Stem Cell Proliferation and Enhances Neurological Function Recovery in Transient Cerebral Ischemic Injury via Activating EGFR/MAPK Signaling Cascades

Radix Astragali (AR) is a commonly used medicinal herb for post-stroke disability in Traditional Chinese Medicine but its active compounds for promoting neurogenic effects are largely unknown. In the present study, we tested the hypothesis that Astragaloside VI could be a promising active compound from AR for adult neurogenesis and brain repair via targeting epidermal growth factor (EGF)-mediated MAPK signaling pathway in post-stroke treatment. By using cultured neural stem cells (NSCs) and experimental stroke rat model, we investigated the effects of Astragaloside VI on inducing NSCs proliferation and self-renewal in vitro, and enhancing neurogenesis for the recovery of the neurological functions in post-ischemic brains in vivo. For animal experiments, rats were undergone 1.5 h middle cerebral artery occlusion (MCAO) plus 7 days reperfusion. Astragaloside VI (2 μg/kg) was daily administrated by intravenous injection (i.v.) for 7 days. Astragaloside VI treatment promoted neurogenesis and astrogenic formation in dentate gyrus zone, subventricular zone, and cortex of the transient ischemic rat brains in vivo. Astragaloside VI treatment enhanced NSCs self-renewal and proliferation in the cultured NSCs in vitro without affecting NSCs differentiation. Western blot analysis showed that Astragaloside VI up-regulated the expression of nestin, p-EGFR and p-MAPK, and increased neurosphere sizes, whose effects were abolished by the co-treatment of EGF receptor inhibitor gefitinib and ERK inhibitor PD98059. Behavior tests revealed that Astragaloside VI promoted the spatial learning and memory and improved the impaired motor function in transient cerebral ischemic rats. Taken together, Astragaloside VI could effectively activate EGFR/MAPK signaling cascades, promote NSCs proliferation and neurogenesis in transient cerebral ischemic brains, and improve the repair of neurological functions in post-ischemic stroke rats. Astragaloside VI could be a new therapeutic drug candidate for post-stroke treatment.

Impaired neural stem cell expansion and hypersensitivity to epileptic seizures in mice lacking the EGFR in the brain

Mice lacking the epidermal growth factor receptor (EGFR) develop an early postnatal degeneration of the frontal cortex and olfactory bulbs and show increased cortical astrocyte apoptosis. The poor health and early lethality of EGFR^−/− mice prevented the analysis of mechanisms responsible for the neurodegeneration and function of the EGFR in the adult brain. Here, we show that postnatal EGFR‐deficient neural stem cells are impaired in their self‐renewal potential and lack clonal expansion capacity in vitro. Mice lacking the EGFR in the brain (EGFR^Δbrain) show low penetrance of cortical degeneration compared to EGFR^−/− mice despite genetic recombination of the conditional allele. Adult EGFR^Δ mice establish a proper blood–brain barrier and perform reactive astrogliosis in response to mechanical and infectious brain injury, but are more sensitive to Kainic acid‐induced epileptic seizures. EGFR‐deficient cortical astrocytes, but not midbrain astrocytes, have reduced expression of glutamate transporters Glt1 and Glast, and show reduced glutamate uptake in vitro, illustrating an excitotoxic mechanism to explain the hypersensitivity to Kainic acid and region‐specific neurodegeneration observed in EGFR‐deficient brains.

Escort cells generate a dynamic compartment for germline stem cell differentiation via combined Stat and Erk signalling

Two different compartments support germline stem cell (GSC) self-renewal and their timely differentiation: the classical niche provides maintenance cues, while a differentiation compartment, formed by somatic escort cells (ECs), is required for proper GSC differentiation. ECs extend long protrusions that invade between tightly packed germ cells, and alternate between encapsulating and releasing them. How ECs achieve this dynamic balance has not been resolved. By combining live imaging and genetic analyses in Drosophila, we have characterised EC shapes and their dynamic changes. We show that germ cell encapsulation by ECs is a communal phenomenon, whereby EC-EC contacts stabilise an extensive meshwork of protrusions. We further show that Signal Transducer and Activator of Transcription (Stat) and Epidermal Growth Factor Receptor (Egfr) signalling sustain EC protrusiveness and flexibility by combinatorially affecting the activity of different RhoGTPases. Our results reveal how a complex signalling network can determine the shape of a cell and its dynamic behaviour. It also explains how the differentiation compartment can establish extensive contacts with germ cells, while allowing a continual posterior movement of differentiating GSC daughters.

ErbB4 protects against neuronal apoptosis via activation of YAP/PIK3CB signaling pathway in a rat model of subarachnoid hemorrhage

Neuronal apoptosis is a central pathological process in subarachnoid hemorrhage (SAH)-induced early brain injury. Previous studies indicated that ErbB4 (EGFR family member v-erb-b2 avian erythroblastic leukemia viral oncogene homolog 4) is essential for normal development and maintenance of the nervous system. In this study, we explored the neuroprotective effects of ErbB4 and its downstream YAP (yes-associated protein)/PIK3CB signaling pathway in early brain injury after SAH in a rat model using the endovascular perforation method. Rats were neurologically evaluated with the Modified Garcia Scale and beam balance test at 24h and 72h after SAH. An ErbB4 activator Neuregulin 1β1 (Nrg 1β1), ErbB4 siRNA and YAP siRNA were used to explore this pathway. The expression of p-ErbB4 and YAP was significantly increased after SAH. Multiple immunofluorescence labeling experiments demonstrated that ErbB4 is mainly expressed in neurons. Activation of ErbB4 and its downstream signals improved the neurological deficits after SAH and significantly reduced neuronal cell death. Inhibition of ErbB4 reduced YAP and PIK3CB expression, and aggravated cell apoptosis. YAP knockdown reduced the PIK3CB level and eliminated the anti-apoptotic effects of ErbB4 activation. These findings indicated that ErbB4 plays a neuroprotective role in early brain injury after SAH, possibly via the YAP/PIK3CB signaling pathway.

The Cellular Prion Protein Controls Notch Signaling in Neural Stem/Progenitor Cells

The prion protein is infamous for its involvement in a group of neurodegenerative diseases known as Transmissible Spongiform Encephalopathies. In the longstanding quest to decipher the physiological function of its cellular isoform, PrP^C , the discovery of its participation to the self-renewal of hematopoietic and neural stem cells has cast a new spotlight on its potential role in stem cell biology. However, still little is known on the cellular and molecular mechanisms at play. Here, by combining in vitro and in vivo murine models of PrP^C depletion, we establish that PrP^C deficiency severely affects the Notch pathway, which plays a major role in neural stem cell maintenance. We document that the absence of PrP^C in a neuroepithelial cell line or in primary neurospheres is associated with drastically reduced expression of Notch ligands and receptors, resulting in decreased levels of Notch target genes. Similar alterations of the Notch pathway are recovered in the neuroepithelium of Prnp^-/- embryos during a developmental window encompassing neural tube closure. In addition, in line with Notch defects, our data show that the absence of PrP^C results in altered expression of Nestin and Olig2 as well as N-cadherin distribution. We further provide evidence that PrP^C controls the expression of the epidermal growth factor receptor (EGFR) downstream from Notch. Finally, we unveil a negative feedback action of EGFR on both Notch and PrP^C . As a whole, our study delineates a molecular scenario through which PrP^C takes part to the self-renewal of neural stem and progenitor cells. Stem Cells 2017;35:754-765.

Excess HB-EGF, which promotes VEGF signaling, leads to hydrocephalus

Heparin binding epidermal growth factor-like growth factor (HB-EGF) is an angiogenic factor mediating radial migration of the developing forebrain, while vascular endothelial growth factor (VEGF) is known to influence rostral migratory stream in rodents. Cell migratory defects have been identified in animal models of hydrocephalus; however, the relationship between HB-EGF and hydrocephalus is unclear. We show that mice overexpressing human HB-EGF with β-galactosidase reporter exhibit an elevated VEGF, localization of β-galactosidase outside the subventricular zone (SVZ), subarachnoid hemorrhage, and ventriculomegaly. In Wistar polycystic kidney rats with hydrocephalus, alteration of migratory trajectory is detected. Furthermore, VEGF infusions into the rats result in ventriculomegaly with an increase of SVZ neuroblast in rostral migratory stream, whereas VEGF ligand inhibition prevents it. Our results support the idea that excess HB-EGF leads to a significant elevation of VEGF and ventricular dilatation. These data suggest a potential pathophysiological mechanism that elevated HB-EGF can elicit VEGF induction and hydrocephalus.

Effects of Transforming Growth Factor Beta 1 in Cerebellar Development: Role in Synapse Formation

Granule cells (GC) are the most numerous glutamatergic neurons in the cerebellar cortex and represent almost half of the neurons of the central nervous system. Despite recent advances, the mechanisms of how the glutamatergic synapses are formed in the cerebellum remain unclear. Among the TGF-β family, TGF-beta 1 (TGF-β1) has been described as a synaptogenic molecule in invertebrates and in the vertebrate peripheral nervous system. A recent paper from our group demonstrated that TGF-β1 increases the excitatory synapse formation in cortical neurons. Here, we investigated the role of TGF-β1 in glutamatergic cerebellar neurons. We showed that the expression profile of TGF-β1 and its receptor, TβRII, in the cerebellum is consistent with a role in synapse formation in vitro and in vivo. It is low in the early postnatal days (P1–P9), increases after postnatal day 12 (P12), and remains high until adulthood (P30). We also found that granule neurons express the TGF-β receptor mRNA and protein, suggesting that they may be responsive to the synaptogenic effect of TGF-β1. Treatment of granular cell cultures with TGF-β1 increased the number of glutamatergic excitatory synapses by 100%, as shown by immunocytochemistry assays for presynaptic (synaptophysin) and post-synaptic (PSD-95) proteins. This effect was dependent on TβRI activation because addition of a pharmacological inhibitor of TGF-β, SB-431542, impaired the formation of synapses between granular neurons. Together, these findings suggest that TGF-β1 has a specific key function in the cerebellum through regulation of excitatory synapse formation between granule neurons.

Maternal dietary intake of choline in mice regulates development of the cerebral cortex in the offspring

Maternal diets low in choline, an essential nutrient, increase the risk of neural tube defects and lead to low performance on cognitive tests in children. However, the consequences of maternal dietary choline deficiency for the development and structural organization of the cerebral cortex remain unknown. In this study, we fed mouse dams either control (CT) or low-choline (LC) diets and investigated the effects of choline on cortical development in the offspring. As a result of a low choline supply between embryonic day (E)11 and E17 of gestation, the number of 2 types of cortical neural progenitor cells (NPCs)-radial glial cells and intermediate progenitor cells-was reduced in fetal brains (P< 0.01). Furthermore, the number of upper layer cortical neurons was decreased in the offspring of dams fed an LC diet at both E17 (P< 0.001) and 4 mo of age (P< 0.001). These effects of LC maternal diet were mediated by a decrease in epidermal growth factor receptor (EGFR) signaling in NPCs related to the disruption of EGFR posttranscriptional regulation. Our findings describe a novel mechanism whereby low maternal dietary intake of choline alters brain development.-Wang, Y., Surzenko, N., Friday, W. B., Zeisel, S. H. Maternal dietary intake of choline in mice regulates development of the cerebral cortex in the offspring.

A neurocentric perspective on glioma invasion

Malignant gliomas are devastating tumours that frequently kill patients within 1 year of diagnosis. The major obstacle to a cure is diffuse invasion, which enables tumours to escape complete surgical resection and chemo- and radiation therapy. Gliomas use the same tortuous extracellular routes of migration that are travelled by immature neurons and stem cells, frequently using blood vessels as guides. They repurpose ion channels to dynamically adjust their cell volume to accommodate to narrow spaces and breach the blood-brain barrier through disruption of astrocytic endfeet, which envelop blood vessels. The unique biology of glioma invasion provides hitherto unexplored brain-specific therapeutic targets for this devastating disease.

Rostral-caudal distribution of Emx1-lineage stem/transit amplifying cells and lineage progression in embryonic cortex depend on Hedgehog signaling

Lineage progression of neural precursors to an EGF-responsive state can be promoted by several extrinsic signals, including fibroblast growth factor 2 (FGF2) and Hedgehog (Hh). It has been suggested that EGF-responsive precursors in the embryonic cerebral cortex originate in the ventral telencephalon in an FGF-dependent manner and migrate dorsally. To determine whether cortical EGF-responsive cells originate locally from dorsal precursors, we marked these precursors using Emx1-cre and the cre reporter Z/EG and observed a local origin for EGF-responsive cells. We also found a rostral-caudal difference in the abundance of self-renewing, neurogenic Emx1-lineage precursors, with more present rostrally. Deleting the Hh receptor smoothened in Emx-1 lineage cells impaired their progression to an EGF-responsive state. Moreover, loss of smoothened increased the proportion of neurogenic, self-renewing Emx1-lineage cells in caudal regions of cortex, eliminating their asymmetric distribution. Our results support the idea that Hh signaling promotes lineage progression of stem/transit amplifying cells, particularly in caudal regions of the embryonic cortex, leading to rostral-caudal differences in the abundance of neurogenic, self-renewing precursors.

Growth/differentiation factor 15 promotes EGFR signalling, and regulates proliferation and migration in the hippocampus of neonatal and young adult mice

The activation of epidermal growth factor receptor (EGFR) affects multiple aspects of neural precursor behaviour, including proliferation and migration. Telencephalic precursors acquire EGF responsiveness and upregulate EGFR expression at late stages of development. The events regulating this process and its significance are still unclear. We here show that in the developing and postnatal hippocampus (HP), growth/differentiation factor (GDF) 15 and EGFR are co-expressed in primitive precursors as well as in more differentiated cells. We also provide evidence that GDF15 promotes responsiveness to EGF and EGFR expression in hippocampal precursors through a mechanism that requires active CXC chemokine receptor (CXCR) 4. Besides EGFR expression, GDF15 ablation also leads to decreased proliferation and migration. In particular, lack of GDF15 impairs both processes in the cornu ammonis (CA) 1 and only proliferation in the dentate gyrus (DG). Importantly, migration and proliferation in the mutant HP were altered only perinatally, when EGFR expression was also affected. These data suggest that GDF15 regulates migration and proliferation by promoting EGFR signalling in the perinatal HP and represent a first description of a functional role for GDF15 in the developing telencephalon.

Microfluidic generated EGF-gradients induce chemokinesis of transplantable retinal progenitor cells via the JAK/STAT and PI3kinase signaling pathways

A growing number of studies are evaluating retinal progenitor cell (RPC) transplantation as an approach to repair retinal degeneration and restore visual function. To advance cell-replacement strategies for a practical retinal therapy, it is important to define the molecular and biochemical mechanisms guiding RPC motility. We have analyzed RPC expression of the epidermal growth factor receptor (EGFR) and evaluated whether exposure to epidermal growth factor (EGF) can coordinate motogenic activity in vitro. Using Boyden chamber analysis as an initial high-throughput screen, we determined that RPC motility was optimally stimulated by EGF concentrations in the range of 20-400 ng/ml, with decreased stimulation at higher concentrations, suggesting concentration-dependence of EGF-induced motility. Using bioinformatics analysis of the EGF ligand in a retina-specific gene network pathway, we predicted a chemotactic function for EGF involving the MAPK and JAK-STAT intracellular signaling pathways. Based on targeted inhibition studies, we show that ligand binding, phosphorylation of EGFR and activation of the intracellular STAT3 and PI3kinase signaling pathways are necessary to drive RPC motility. Using engineered microfluidic devices to generate quantifiable steady-state gradients of EGF coupled with live-cell tracking, we analyzed the dynamics of individual RPC motility. Microfluidic analysis, including center of mass and maximum accumulated distance, revealed that EGF induced motility is chemokinetic with optimal activity observed in response to low concentration gradients. Our combined results show that EGFR expressing RPCs exhibit enhanced chemokinetic motility in the presence of low nanomole levels of EGF. These findings may serve to inform further studies evaluating the extent to which EGFR activity, in response to endogenous ligand, drives motility and migration of RPCs in retinal transplantation paradigms.

Receptor tyrosine kinase (RTK) signalling in the control of neural stem and progenitor cell (NSPC) development

Important developmental responses are elicited in neural stem and progenitor cells (NSPC) by activation of the receptor tyrosine kinases (RTK), including the fibroblast growth factor receptors, epidermal growth factor receptor, platelet-derived growth factor receptors and insulin-like growth factor receptor (IGF1R). Signalling through these RTK is necessary and sufficient for driving a number of developmental processes in the central nervous system. Within each of the four RTK families discussed here, receptors are activated by sets of ligands that do not cross-activate receptors of the other three families, and therefore, their activation can be independently regulated by ligand availability. These RTK pathways converge on a conserved core of signalling molecules, but differences between the receptors in utilisation of signalling molecules and molecular adaptors for intracellular signal propagation become increasingly apparent. Intracellular inhibitors of RTK signalling are widely involved in the regulation of developmental signalling in NSPC and often determine developmental outcomes of RTK activation. In addition, cellular responses of NSPC to the activation of a given RTK may be significantly modulated by signal strength. Cellular propensity to respond also plays a role in developmental outcomes of RTK signalling. In combination, these mechanisms regulate the balance between NSPC maintenance and differentiation during development and in adulthood. Attribution of particular developmental responses of NSPC to specific pathways of RTK signalling becomes increasingly elucidated. Co-activation of several RTK in developing NSPC is common, and analysis of co-operation between their signalling pathways may advance knowledge of RTK role in NSPC development.

Integrative mechanisms of oriented neuronal migration in the developing brain

The emergence of functional neuronal connectivity in the developing cerebral cortex depends on neuronal migration. This process enables appropriate positioning of neurons and the emergence of neuronal identity so that the correct patterns of functional synaptic connectivity between the right types and numbers of neurons can emerge. Delineating the complexities of neuronal migration is critical to our understanding of normal cerebral cortical formation and neurodevelopmental disorders resulting from neuronal migration defects. For the most part, the integrated cell biological basis of the complex behavior of oriented neuronal migration within the developing mammalian cerebral cortex remains an enigma. This review aims to analyze the integrative mechanisms that enable neurons to sense environmental guidance cues and translate them into oriented patterns of migration toward defined areas of the cerebral cortex. We discuss how signals emanating from different domains of neurons get integrated to control distinct aspects of migratory behavior and how different types of cortical neurons coordinate their migratory activities within the developing cerebral cortex to produce functionally critical laminar organization.

ADAM17 is critical for multipolar exit and radial migration of neuronal intermediate progenitor cells in mice cerebral cortex

The radial migration of neuronal progenitor cells is critical for the development of cerebral cortex layers. They go through a critical step transforming from multipolar to bipolar before outward migration. A Disintegrin and Metalloprotease 17 (ADAM17) is a transmembrane protease which can process many substrates involved in cell-cell interaction, including Notch, ligands of EGFR, and some cell adhesion molecules. In this study, we used in utero electroporation to knock down or overexpress ADAM17 at embryonic day 14.5 (E14.5) in neuronal progenitor cells to examine the role of ADAM17 in cortical embryonic neurogenesis. Our results showed that the radial migration of ADAM17-knocked down cells were normal till E16.5 and reached the intermediate zone (IZ). Then most transfected cells stopped migration and stayed at the IZ to inner cortical plate (CP) layer at E18.5, and there was higher percentage of multipolar cells at IZ layer in the ADAM17-knocked down group compared to the cells in control group. Marker staining revealed that those ADAM17-knocked down cells differentiated normally from neural stem cells (NSCs) to neuronal intermediate progenitor cells (nIPCs) but did not differentiate into mature neurons. The migration and multipolar exit defects caused by ADAM17 knockdown could be partially rescued by over-expressing an shRNA resistant ADAM17, while overexpressing ADAM17 alone did not affect the radial migration. Taken together, our results showed for the first time that, ADAM17 is critical in regulating the multipolar-stage exit and radial migration of the nIPCs during telencephalon cortex development in mice.

EGF transactivation of Trk receptors regulates the migration of newborn cortical neurons

The development of neuronal networks in the neocortex depends on control mechanisms for mitosis and migration that allow newborn neurons to find their accurate position. Multiple mitogens, neurotrophic factors, guidance molecules and their corresponding receptors are involved in this process, but the mechanisms by which these signals are integrated are only poorly understood. We found that TrkB and TrkC, the receptors for brain-derived neurotrophic factor (BDNF) and neurotrophin-3 (NT-3), are activated by epidermal growth factor receptor (EGFR) signaling rather than by BDNF or NT-3 in embryonic mouse cortical precursor cells. This transactivation event regulated migration of early neuronal cells to their final position in the developing cortex. Transactivation by EGF led to membrane translocation of TrkB, promoting its signaling responsiveness. Our results provide genetic evidence that TrkB and TrkC activation in early cortical neurons do not depend on BDNF and NT-3, but instead on transactivation by EGFR signaling.

Adult periventricular neural stem cells: outstanding progress and outstanding issues

Twenty years have past since the existence of neural stem cells (NSCs) within the walls of the adult lateral ventricles was discovered. During this period of time, great strides have been made in every facet of our understanding of this adult periventricular NSC population. In this review, some of the fields' major advancements regarding the nature and function of adult periventricular NSCs are examined. We bring attention to issues related to NSC identity, potential, and the role of Notch signaling in regulating quiescence and activation that warrant further investigation. Progress in the understanding of human adult NSCs will aid in the development of tools required to advance therapies not only for brain repair after injury or disease but may also lead to novel therapeutics for brain tumors.

Functions of neurotrophins and growth factors in neurogenesis and brain repair

The identification and isolation of multipotent neural stem and progenitor cells in the brain, giving rise to neurons, astrocytes, and oligodendrocytes initiated many studies in order to understand basic mechanisms of endogenous neurogenesis and repair mechanisms of the nervous system and to develop novel therapeutic strategies for cellular regeneration therapies in brain disease. A previous review (Trujillo et al., Cytometry A 2009;75:38-53) focused on the importance of extrinsic factors, especially neurotransmitters, for directing migration and neurogenesis in the developing and adult brain. Here, we extend our review discussing the effects of the principal growth and neurotrophic factors as well as their intracellular signal transduction on neurogenesis, fate determination and neuroprotective mechanisms. Many of these mechanisms have been elucidated by in vitro studies for which neural stem cells were isolated, grown as neurospheres, induced to neural differentiation under desired experimental conditions, and analyzed for embryonic, progenitor, and neural marker expression by flow and imaging cytometry techniques. The better understanding of neural stem cells proliferation and differentiation is crucial for any therapeutic intervention aiming at neural stem cell transplantation and recruitment of endogenous repair mechanisms.

Heparin-binding epidermal growth factor-like growth factor promotes murine enteric nervous system development and enteric neural crest cell migration

BACKGROUND/PURPOSE

Developmental defects of the enteric nervous system lead to a variety of disorders including Hirschprung disease. We have previously shown that heparin-binding epidermal growth factor-like growth factor (HB-EGF) exerts neuroprotective effects on injured neurons. The goals of this study were to assess the role of HB-EGF in enteric nervous system development and to evaluate the effect of HB-EGF on enteric neural crest-derived cell (ENCC) migration in the developing gastrointestinal tract of mice.

MATERIALS AND METHODS

HB-EGF immunohistochemistry was used to examine HB-EGF protein expression in the hindgut of embryonic mice. Gut specimens were stained for PGP9.5 (a neuronal cell marker) to examine the extent of ENCC migration in the intestine at different embryonic stages in HB-EGF knockout (KO) and wild-type (WT) mice. Embryonic gut organ cultures were established to examine the effect of HB-EGF on ENCC migration.

RESULTS

The expression of HB-EGF was limited to the endodermal epithelium of the hindgut in early gestation, but rapidly involved the hindgut mesenchyme after ENCC migrated into this region. ENCC migration was significantly delayed in HB-EGF KO compared with WT embryos, leading to defects in neural colonization of the distal gut in postnatal HB-EGF KO mice. Addition of HB-EGF to WT embryonic intestine significantly promoted ENCC migration, as demonstrated by a significant increase in the ratio of ENCC migration distance toward the distal hindgut/total colon length (78% ± 4% vs 53% ± 2%, P = .001).

CONCLUSIONS

Deletion of the HB-EGF gene leads to enteric nervous system developmental defects. HB-EGF stimulates ENCC migration in the gut, supporting a potential role for administration of HB-EGF in the future for the treatment of patients with intestinal neuronal disorders.

Akt1 interacts with epidermal growth factor receptors and hedgehog signaling to increase stem/transit amplifying cells in the embryonic mouse cortex

A subset of precursors in the embryonic mouse cortex and in neurospheres expresses a higher level of the serine/threonine kinase Akt1 than neighboring precursors. We reported previously that the functional significance of high Akt1 expression was enhanced Akt1 activity, resulting in an increase in survival, proliferation, and self-renewal of multipotent stem/transit amplifying cells. Akt1 can interact with a number of signaling pathways, but the extrinsic factors that are required for specific effects of elevated Akt1 expression have not been identified. In this study we addressed the contributions of signaling via epidermal growth factor (EGF) and hedgehog (Hh) receptors. In EGF receptor-null precursors or following transient inhibition of EGF receptor tyrosine kinase activity, elevating Akt1 by retroviral transduction could still increase survival and proliferation but could not increase self-renewal. We also found that elevated Akt1 expression induced the expression of EGF receptors (EGFRs) in wild-type precursors. Several extrinsic factors, including Shh, can induce EGFR expression by cortical precursors, and we found that elevating Akt1 allowed them to respond to a subthreshold concentration of Shh to induce EGFRs. In precursors that lack the Hh receptor smoothened, however, elevating Akt1 did not increase EGFR expression or self-renewal, though it could still stimulate proliferation. These findings suggest that a subset of precursors in the embryonic cortex that express an elevated level of Akt1 can respond to lower concentrations of Shh than neighboring precursors, resulting in an increase in their expression of EGFRs. Signaling via EGFRs is required for their self-renewal.

Specific sets of intrinsic and extrinsic factors drive excitatory and inhibitory circuit formation

How are excitatory (glutamatergic) and inhibitory (GABAergic) synapses established? Do distinct molecular mechanisms direct differentiation of glutamatergic and GABAergic synapses? In the brain, glutamatergic and GABAergic synaptic connections are formed with specific patterns. To establish such precise synaptic patterns, neurons pass through multiple checkpoints during development, such as cell fate determination, cell migration and localization, axonal guidance and target recognition, and synapse formation. Each stage offers key molecules for neurons/synapses to obtain glutamatergic or GABAergic specificity. Some mechanisms are based on intrinsic systems to induce gene expression, whereas others are based on extrinsic systems mediated by cell-cell or axon-target interactions. Recent studies indicate that specific formation of glutamatergic and GABAergic synapses is controlled by the expression or activation of different sets of molecules during development. In this review, the authors outline stages critical to the determination of glutamatergic or GABAergic specificity and describe molecules that act as determinants of specificities in each stage, with a particular focus on the synapse formation stage. They also discuss possible mechanisms underlying glutamatergic and GABAergic synapse formation via synapse-type specific synaptic organizers.

Application of in utero electroporation and live imaging in the analyses of neuronal migration during mouse brain development

Correct neuronal migration is crucial for brain architecture and function. During cerebral cortex development (corticogenesis), excitatory neurons generated in the proliferative zone of the dorsal telencephalon (mainly ventricular zone) move through the intermediate zone and migrate past the neurons previously located in the cortical plate and come to rest just beneath the marginal zone. The in utero electroporation technique is a powerful method for rapid gain- and loss-of-function studies of neuronal development, especially neuronal migration. This method enabled us to introduce genes of interest into ventricular zone progenitor cells of mouse embryos and to observe resulting phenotypes such as proliferation, migration, and cell morphology at later stages. In this Award Lecture Review, we focus on the application of the in utero electroporation method to functional analyses of cytoskeleton-related protein septin. We then refer to, as an advanced technique, the in utero electroporation-based real-time imaging method for analyses of cell signaling regulating neuronal migration. The in utero electroporation method and its application would contribute to medical molecular morphology through identification and characterization of the signaling pathways disorganized in various neurological and psychiatric disorders.

Cell-autonomous and cell-to-cell signalling events in normal and altered neuronal migration

The cerebral cortex is a complex six-layered structure that contains an important diversity of neurons, and has rich local and extrinsic connectivity. Among the mechanisms governing the cerebral cortex construction, neuronal migration is perhaps the most crucial as it ensures the timely formation of specific and selective neuronal circuits. Here, we review the main extrinsic and extrinsic factors involved in regulating neuronal migration in the cortex and describe some environmental factors interfering with their actions.

Central role of the EGF receptor in neurometabolic aging

A strong connection between neuronal and metabolic health has been revealed in recent years. It appears that both normal and pathophysiological aging, as well as neurodegenerative disorders, are all profoundly influenced by this "neurometabolic" interface, that is, communication between the brain and metabolic organs. An important aspect of this "neurometabolic" axis that needs to be investigated involves an elucidation of molecular factors that knit these two functional signaling domains, neuronal and metabolic, together. This paper attempts to identify and discuss a potential keystone signaling factor in this "neurometabolic" axis, that is, the epidermal growth factor receptor (EGFR). The EGFR has been previously demonstrated to act as a signaling nexus for many ligand signaling modalities and cellular stressors, for example, radiation and oxidative radicals, linked to aging and degeneration. The EGFR is expressed in a wide variety of cells/tissues that pertain to the coordinated regulation of neurometabolic activity. EGFR signaling has been highlighted directly or indirectly in a spectrum of neurometabolic conditions, for example, metabolic syndrome, diabetes, Alzheimer's disease, cancer, and cardiorespiratory function. Understanding the positioning of the EGFR within the neurometabolic domain will enhance our appreciation of the ability of this receptor system to underpin highly complex physiological paradigms such as aging and neurodegeneration.

The extracellular matrix molecule tenascin C modulates expression levels and territories of key patterning genes during spinal cord astrocyte specification

The generation of astrocytes during the development of the mammalian spinal cord is poorly understood. Here, we demonstrate for the first time that the extracellular matrix glycoprotein tenascin C regulates the expression of key patterning genes during late embryonic spinal cord development, leading to a timely maturation of gliogenic neural precursor cells. We first show that tenascin C is expressed by gliogenic neural precursor cells during late embryonic development. The loss of tenascin C leads to a sustained generation and delayed migration of Fgfr3-expressing immature astrocytes in vivo. Consistent with an increased generation of astroglial cells, we documented an increased number of GFAP-positive astrocytes at later stages. Mechanistically, we could demonstrate an upregulation and domain shift of the patterning genes Nkx6.1 and Nkx2.2 in vivo. In addition, sulfatase 1, a known downstream target of Nkx2.2 in the ventral spinal cord, was also upregulated. Sulfatase 1 regulates growth factor signalling by cleaving sulphate residues from heparan sulphate proteoglycans. Consistent with this function, we observed changes in both FGF2 and EGF responsiveness of spinal cord neural precursor cells. Taken together, our data implicate Tnc in the regulation of proliferation and lineage progression of astroglial progenitors in specific domains of the developing spinal cord.

Drosophila melanogaster as a model system for human brain cancers

Glioblastomas (GBM), the most common primary brain tumors, infiltrate the brain, grow rapidly, and are refractory to current therapies. Signature genetic lesions in glioblastomas include mutation of the epidermal growth factor receptor tyrosine kinase (EGFR) receptor tyrosine kinase and activating mutations in components of the PI-3 kinase (PI3K) pathway. Despite years of study, how these pathways specifically regulate glial pathogenesis is unclear. To address the genetic and cellular origins of this disease, a novel Drosophila GBM model has been developed in which glial progenitor cells give rise to proliferative and invasive neoplastic cells that create transplantable tumors in response to constitutive co-activation of the EGFR-Ras and PI3K pathways. Standing with a rich literature demonstrating the direct relevance of Drosophila to studies on human cancer, neurological disease, and neurodevelopment, this model represents a robust cell-type specific Drosophila neurological disease model in which malignant cells are created by mutations in genetic pathways thought to be driving forces in a homologous human disease. Using lineage analysis and cell-type specific markers, neoplastic glial cells were found to originate from committed glial progenitor cells, rather than from multipotent neuroblasts. Genetic analyses demonstrated that EGFR-Ras and PI3K induce fly glial neoplasia through activation of a combinatorial genetic network composed, in part, of other genetic pathways also commonly mutated in human glioblastomas. In the future, large-scale forward genetic screens with this model may reveal new insights into the origins and treatments of human glioblastoma.

Oligodendrogenesis in the subventricular zone and the role of epidermal growth factor

Demyelinating diseases are characterized by an extensive loss of oligodendrocytes and myelin sheaths from axolemma. These neurological disorders are a common cause of disability in young adults, but so far, there is no effective treatment against them. It has been suggested that neural stem cells (NSCs) may play an important role in brain repair therapies. NSCs in the adult subventricular zone (SVZ), also known as Type-B cells, are multipotential cells that can self-renew and give rise to neurons and glia. Recent findings have shown that cells derived from SVZ Type-B cells actively respond to epidermal-growth-factor (EGF) stimulation becoming highly migratory and proliferative. Interestingly, a subpopulation of these EGF-activated cells expresses markers of oligodendrocyte precursor cells (OPCs). When EGF administration is removed, SVZ-derived OPCs differentiate into myelinating and pre-myelinating oligodendrocytes in the white matter tracts of corpus callosum, fimbria fornix and striatum. In the presence of a demyelinating lesion, OPCs derived from EGF-stimulated SVZ progenitors contribute to myelin repair. Given their high migratory potential and their ability to differentiate into myelin-forming cells, SVZ NSCs represent an important endogenous source of OPCs for preserving the oligodendrocyte population in the white matter and for the repair of demyelinating injuries.

EGF induces CREB and ERK activation at the wall of the mouse lateral ventricles

The subependymal zone at the lateral ventricular wall represents a major neurogenic niche of the adult mammalian brain and continuously provides new neurons for the olfactory bulb. A mosaic of stem and progenitor cells in this niche has the potential to respond to multiple signals including growth factors such as EGF. Recent studies using long-term ventricular infusion of EGF demonstrate intense cell proliferation around the ventricular wall, implicating the presence of EGF-reactive cells also outside the classical neurogenic lateral niche. Here we show that intraventricular injection of EGF induces within minutes CREB and ERK phosphorylation in astrocyte-like progenitor cells (type B cells) and EGF receptor-expressing transit-amplifying progenitor cells-both in the striatal and septal ventricular walls. EGF infusion for 6 days induced continued CREB and ERK activation in nestin+ cells paralleled by intense periventricular cell proliferation. In addition, the ependyma became EGF receptor-immunoreactive, revealed intense CREB phosphorylation and underwent partial de-differentiation. Our results demonstrate that intraventricular application of EGF induces CREB and ERK phosphorylation along the entire ventricular walls and thus permits a direct identification of EGF-responsive cell types. They further support the notion that not only the striatal ventricular wall where the SEZ is located but also the septal ventricular wall carries latent potential for the formation of neurons and glial cells.

Thyroid hormone induces cerebellar neuronal migration and Bergmann glia differentiation through epidermal growth factor/mitogen-activated protein kinase pathway

Cerebellar development in the postnatal period is mainly characterized by an intense cellular proliferation in the external granular layer, followed by migration of granular cells in the molecular layer along the Bergmann glia (BG) fibers. Cerebellar ontogenesis undergoes dramatic modulation by thyroid hormones (THs), although their mechanism of action in this organ is still largely unknown. We previously demonstrated that THs induce astrocytes to secrete epidermal growth factor (EGF), which thus promotes cerebellar neuronal proliferation and extracellular matrix remodeling in vitro. In the present study, we investigated the effect of the TH/EGF pathway on granule neuronal migration. By taking advantage of rat explant and dissociated culture assays, we showed that cerebellar astrocytes treated with TH promote granule cell migration. The addition of neutralizing antibodies against EGF or the pharmacological inhibitor of EGF signaling, bis-tyrphostin, completely inhibited TH-astrocyte-induced migration. Likewise, the addition of EGF itself greatly increased neuronal migration. Treatment of BG-dissociated cultures by EGF dramatically induced an alteration in cell morphology, characterized by an elongation in the glial process. Both neuronal migration and BG elongation were inhibited by the mitogen-activated protein kinase pathway inhibitor PD98059, suggesting that these events might be associated. Together, our results suggest that, by inducing EGF secretion, THs promote neuronal migration through BG elongation. Our data provide new clues to the molecular mechanism of THs in cerebellar development, and may contribute to a better understanding of some neuroendocrine disorders associated with migration deficits.

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.

Epidermal growth factor induces the progeny of subventricular zone type B cells to migrate and differentiate into oligodendrocytes

New neurons and oligodendrocytes are continuously produced in the subventricular zone (SVZ) of adult mammalian brains. Under normal conditions, the SVZ primary precursors (type B1 cells) generate type C cells, most of which differentiate into neurons, with a small subpopulation giving rise to oligodendrocytes. Epidermal growth factor (EGF) signaling induces dramatic proliferation and migration of SVZ progenitors, a process that could have therapeutic applications. However, the fate of cells derived from adult neural stem cells after EGF stimulation remains unknown. Here, we specifically labeled SVZ B1 cells and followed their progeny after a 7-day intraventricular infusion of EGF. Cells derived from SVZ B1 cells invaded the parenchyma around the SVZ into the striatum, septum, corpus callosum, and fimbria-fornix. Most of these B1-derived cells gave rise to cells in the oligodendrocyte lineage, including local NG2+ progenitors, and pre-myelinating and myelinating oligodendrocytes. SVZ B1 cells also gave rise to a population of highly-branched S100beta+/glial fibrillary acidic protein (GFAP)+ cells in the striatum and septum, but no neuronal differentiation was observed. Interestingly, when demyelination was induced in the corpus callosum by a local injection of lysolecithin, an increased number of cells derived from SVZ B1 cells and stimulated to migrate and proliferate by EGF infusion differentiated into oligodendrocytes at the lesion site. This work indicates that EGF infusion can greatly expand the number of progenitors derived from the SVZ primary progenitors which migrate and differentiate into oligodendroglial cells. This expanded population could be used for the repair of white matter lesions.

PKCdelta regulates cortical radial migration by stabilizing the Cdk5 activator p35

Cyclin-dependent kinase 5 (Cdk5) and its activator p35 are critical for radial migration and lamination of cortical neurons. However, how this kinase is regulated by extracellular and intracellular signals during cortical morphogenesis remains unclear. Here, we show that PKCdelta, a member of novel PKC expressing in cortical neurons, could stabilize p35 by direct phosphorylation. PKCdelta attenuated the degradation of p35 but not its mutant derivative, which could not be phosphorylated by PKCdelta. Down-regulation of PKCdelta by in utero electroporation of specific small interference RNA (siRNA) severely impaired the radial migration of cortical neurons. This migration defect was similar to that caused by down-regulation of p35 and could be prevented by cotransfection with the wild-type but not the mutant p35. Furthermore, PKCdelta could be activated by the promigratory factor brain-derived neurotrophic factor (BDNF) and was required for the activation of Cdk5 by BDNF. Both PKCdelta and p35 were required for the promigratory effect of BDNF on cultured newborn neurons. Thus, PKCdelta may promote cortical radial migration through maintaining the proper level of p35 in newborn neurons.

Brain injury expands the numbers of neural stem cells and progenitors in the SVZ by enhancing their responsiveness to EGF

There is an increase in the numbers of neural precursors in the SVZ (subventricular zone) after moderate ischaemic injuries, but the extent of stem cell expansion and the resultant cell regeneration is modest. Therefore our studies have focused on understanding the signals that regulate these processes towards achieving a more robust amplification of the stem/progenitor cell pool. The goal of the present study was to evaluate the role of the EGFR [EGF (epidermal growth factor) receptor] in the regenerative response of the neonatal SVZ to hypoxic/ischaemic injury. We show that injury recruits quiescent cells in the SVZ to proliferate, that they divide more rapidly and that there is increased EGFR expression on both putative stem cells and progenitors. With the amplification of the precursors in the SVZ after injury there is enhanced sensitivity to EGF, but not to FGF (fibroblast growth factor)-2. EGF-dependent SVZ precursor expansion, as measured using the neurosphere assay, is lost when the EGFR is pharmacologically inhibited, and forced expression of a constitutively active EGFR is sufficient to recapitulate the exaggerated proliferation of the neural stem/progenitors that is induced by hypoxic/ischaemic brain injury. Cumulatively, our results reveal that increased EGFR signalling precedes that increase in the abundance of the putative neural stem cells and our studies implicate the EGFR as a key regulator of the expansion of SVZ precursors in response to brain injury. Thus modulating EGFR signalling represents a potential target for therapies to enhance brain repair from endogenous neural precursors following hypoxic/ischaemic and other brain injuries.

In situ hybridization reveals developmental regulation of ErbB1-4 mRNA expression in mouse midbrain: implication of ErbB receptors for dopaminergic neurons

Although epidermal growth factor (EGF) and neuregulin-1 are neurotrophic factors for mesencephalic dopaminergic neurons and implicated in schizophrenia, the cellular localization and developmental regulation of their receptors (ErbB1-4) remain to be characterized. Here we investigated the distributions of mRNA for ErbB1-4 in the midbrain of the developing mouse with in situ hybridization and immunohistochemistry. The expression of ErbB1 and ErbB2 mRNAs was relatively high at the perinatal stage and frequently colocalized with mRNA for S100beta and Olig2, markers for immature astrocytes or oligodendrocyte precursors. Modest signal for ErbB1 mRNA was also detected in a subset of dopaminergic neurons. ErbB3 mRNA was detectable at postnatal day 10, peaked at postnatal day 18, and colocalized with 2',3'-cyclic nucleotide 3'-phosphodiesterase, a marker for oligodendrocytes. In contrast, ErbB4 mRNA was exclusively localized in neurons throughout development. Almost all of ErbB4 mRNA-expressing cells (94%-96%) were positive for tyrosine hydroxylase in the substantia nigra pars compacta but 66%-78% in the ventral tegmental area and substantia nigra pars lateralis. Conversely, 92%-99% of tyrosine hydroxylase-positive cells expressed ErbB4 mRNA. The robust and restricted expression of ErbB4 mRNA in the midbrain dopaminergic neurons suggests that ErbB4 ligands, neuregulin-1 and other EGF-related molecules, contribute to development or maintenance of this neuronal population.

Differential regulation of telencephalic pallial-subpallial boundary patterning by Pax6 and Gsh2

In the embryonic telencephalon, the pallial-subpallial boundary (PSB) separates the dorsal Pax6+ pallium from the ventral Gsh2+ subpallium. Previous studies have revealed that this region is a source of cells that will populate both the olfactory bulb and basal telencephalic limbic system. However, the level of progenitor cell heterogeneity and developmental genetic regulation of this progenitor region remains to be fully elucidated. In this study we carried out a comprehensive analysis of gene expression patterns at the PSB, in addition to an examination of the combinatorial function of Pax6 and Gsh2 in the specification of the PSB. First, we reveal that the PSB is comprised of a complex mix of molecularly distinct progenitor pools. In addition, by analysis of single Sey, Gsh2, and Sey/Gsh2 double mutant mice, we demonstrate that both Pax6 and Gsh2 are directly required for major aspects of PSB progenitor specification. Our analysis also reveals that the establishment of the epidermal growth factor receptor positive lateral cortical stream migratory route to the basal telencephalon is Pax6 dependent. Thus, in addition to their well-characterized cross-repressive roles in dorsal/ventral patterning our analyses reveal important novel functions of Gsh2 and Pax6 in the regulation of PSB progenitor pool specification and patterning.

Specific developmental reductions in subventricular zone ErbB1 and ErbB4 mRNA in the human brain

The primate postnatal subventricular zone (SVZ) lies under the ventrolateral borders of the lateral ventricles as a discrete region of cells with gliogenic and neurogenic capacity regulated by ErbB receptors. However, the specific role of each ErbB subtype in SVZ cell development remains unclear, particularly in the human brain. The postnatal spatial and temporal expression profile of ErbB subtypes in the human brain may provide valuable insight into their distinct functions in the SVZ following birth. Hence, we examined the expression profile of ErbB1, ErbB2, ErbB3 and ErbB4 mRNA in the SVZ of human postmortem brains from neonates, infants, toddlers, school age subjects, adolescents, young adults and adults using in situ hybridization. SVZ transcript levels of ErbB1 and ErbB4 were highest in neonates and diminished with age. SVZ ErbB4 mRNA quantities significantly decreased by >85% to almost undetectable levels after the first year of life, while SVZ ErbB1 transcript levels displayed more gradual reductions, stabilizing to approximately 30-40% of neonate levels after the age of 5 years. In the neonate and infant SVZ, ErbB4 mRNA was localized to cell clusters resembling migratory neuroblast aggregates whereas ErbB1 mRNA was expressed in cells along but not within these clusters. ErbB2 mRNA appeared to be constantly expressed in the human SVZ at all postnatal ages as opposed to ErbB3 transcripts, which were not detected in the human SVZ at any age following birth. These findings suggest that ErbB1 and ErbB4 may play more salient roles than ErbB2 and ErbB3 in mediating early postnatal neurodevelopmental events. In addition, ErbB1- and ErbB4-immunoreactive cells and fibers were extensive throughout the human infant SVZ, but did not appear to overlap with PSA-NCAM-immunopositive clusters. The restriction of robust SVZ ErbB4 expression to neonate and infant age groups may indicate that SVZ-derived ErbB4-dependent postnatal neuronal development is most extensive within a narrow time frame early after birth.

Inhibition of matrix metalloproteinase-9 attenuated neural progenitor cell migration after photothrombotic ischemia

Recent studies have shown that neuroblasts migrate from the subventricular zone (SVZ) into the injured area after ischemic brain insults. However, it is not well understood which mechanism mediates this ectopic migration and which types of cells migrate into the damaged region from the SVZ. The present study was designed to investigate the characteristics of the migration of nestin-positive neural stem cells toward the region of ischemic injury after focal cortical ischemia. Nestin-eGFP transgenic mice were used to effectively model the migration of SVZ cells. Photothrombotic ischemia was induced by injection of rose bengal (30 mg/kg) and exposure to cold light. Migration of nestin-positive cells was examined using 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) and bromodeoxyuridine (BrdU) labeling. The number of nestin-positive cells was increased significantly in the peri-infarct area at 5 and 7 days after photothrombosis. A subset of nestin-positive cells was co-labeled with DiI or BrdU. Some of the nestin-positive cells co-expressed doublecortin (DCX) and only a few nestin-positive cells co-labeled with anti-epidermal growth factor receptor (EGFr) antibody. However, no nestin-positive cells were immunoreactive for glial fibrillary acidic protein (GFAP). The inhibition of matrix metalloproteinases (MMPs) using the MMP inhibitor, FN-439, decreased nestin-positive cells in the peri-infarct region at 7 days after photothrombosis. Although MMP-9 was not co-expressed in the nestin-positive cells in the peri-infarct cortex, MMP-9 did co-localize with GFAP-positive astrocytes. These results suggest that nestin-positive neural progenitor cells migrate into the peri-infarct cortex after photothrombotic ischemia and that MMP-9 is involved in the migration.