Neuraminidase inhibition promotes the collective migration of neurons and recovery of brain function

In the injured brain, new neurons produced from endogenous neural stem cells form chains and migrate to injured areas and contribute to the regeneration of lost neurons. However, this endogenous regenerative capacity of the brain has not yet been leveraged for the treatment of brain injury. Here, we show that in healthy brain chains of migrating new neurons maintain unexpectedly large non-adherent areas between neighboring cells, allowing for efficient migration. In instances of brain injury, neuraminidase reduces polysialic acid levels, which negatively regulates adhesion, leading to increased cell-cell adhesion and reduced migration efficiency. The administration of zanamivir, a neuraminidase inhibitor used for influenza treatment, promotes neuronal migration toward damaged regions, fosters neuronal regeneration, and facilitates functional recovery. Together, these findings shed light on a new mechanism governing efficient neuronal migration in the adult brain under physiological conditions, pinpoint the disruption of this mechanism during brain injury, and propose a promising therapeutic avenue for brain injury through drug repositioning.

Migratory Response of Cells in Neurogenic Niches to Neuronal Death: The Onset of Harmonic Repair?

Harmonic mechanisms orchestrate neurogenesis in the healthy brain within specific neurogenic niches, which generate neurons from neural stem cells as a homeostatic mechanism. These newly generated neurons integrate into existing neuronal circuits to participate in different brain tasks. Despite the mechanisms that protect the mammalian brain, this organ is susceptible to many different types of damage that result in the loss of neuronal tissue and therefore in alterations in the functionality of the affected regions. Nevertheless, the mammalian brain has developed mechanisms to respond to these injuries, potentiating its capacity to generate new neurons from neural stem cells and altering the homeostatic processes that occur in neurogenic niches. These alterations may lead to the generation of new neurons within the damaged brain regions. Notwithstanding, the activation of these repair mechanisms, regeneration of neuronal tissue within brain injuries does not naturally occur. In this review, we discuss how the different neurogenic niches respond to different types of brain injuries, focusing on the capacity of the progenitors generated in these niches to migrate to the injured regions and activate repair mechanisms. We conclude that the search for pharmacological drugs that stimulate the migration of newly generated neurons to brain injuries may result in the development of therapies to repair the damaged brain tissue.

Amphiphilic peptide-tagged N-cadherin forms radial glial-like fibers that enhance neuronal migration in injured brain and promote sensorimotor recovery

The mammalian brain has very limited ability to regenerate lost neurons and recover function after injury. Promoting the migration of young neurons (neuroblasts) derived from endogenous neural stem cells using biomaterials is a new and promising approach to aid recovery of the brain after injury. However, the delivery of sufficient neuroblasts to distant injured sites is a major challenge because of the limited number of scaffold cells that are available to guide neuroblast migration. To address this issue, we have developed an amphiphilic peptide [(RADA)₃-(RADG)] (mRADA)-tagged N-cadherin extracellular domain (Ncad-mRADA), which can remain in mRADA hydrogels and be injected into deep brain tissue to facilitate neuroblast migration. Migrating neuroblasts directly contacted the fiber-like Ncad-mRADA hydrogel and efficiently migrated toward an injured site in the striatum, a deep brain area. Furthermore, application of Ncad-mRADA to neonatal cortical brain injury efficiently promoted neuronal regeneration and functional recovery. These results demonstrate that self-assembling Ncad-mRADA peptides mimic both the function and structure of endogenous scaffold cells and provide a novel strategy for regenerative therapy.

Engineering 3D Cortical Spheroids for an In Vitro Ischemic Stroke Model

Three-dimensional (3D) spheroids composed of brain cells have shown great potential to mimic the pathophysiology of the brain. However, a 3D spheroidal brain-disease model for cerebral ischemia has not been reported. This study investigated an ultralow attachment (ULA) surface-mediated formation of 3D cortical spheroids using primary rat cortical cells to recapitulate the cerebral ischemic responses in stroke by oxygen-glucose deprivation-reoxygenation (OGD-R) treatment. Comparison between two-dimensional (2D) and 3D cell culture models confirmed the better performance of the 3D cortical spheroids as normal brain models. The cortical cells cultured in 3D maintained their healthy physiological morphology of a less activated state and suppressed mRNA expressions of pathological stroke markers, S100B, IL-1β, and MBP, selected based on in vivo stroke model. Interestingly, the spheroids formed on the ULA surface exhibited striking aggregation dynamics involving active cell-substrate interactions, whereas those formed on the agarose surface aggregated passively by the convective flow of the media. Accordingly, ULA spheroids manifested a layered arrangement of neurons and astrocytes with higher expressions of integrin β1, integrin α5, N-cadherin, and fibronectin than the agarose spheroids. OGD-R-induced stroke model of the ULA spheroids successfully mimicked the ischemic response as evidenced by the upregulated mRNA expressions of the key markers for stroke, S100B, IL-1β, and MBP. Our study suggested that structurally and functionally distinct cortical spheroids could be generated by simply tuning the cell-substrate binding activities during dynamic spheroidal formation, which should be an essential factor to consider in establishing a brain-disease model.

Tumor Spheroids of an Aggressive Form of Central Neurocytoma Have Transit-Amplifying Progenitor Characteristics with Enhanced EGFR and Tumor Stem Cell Signaling

Central neurocytoma (CN) has been known as a benign neuronal tumor. In rare cases, CN undergoes malignant transformation to glioblastomas (GBM). Here we examined its cellular origin by characterizing differentiation potential and gene expression of CN-spheroids. First, we demonstrate that both CN tissue and cultured primary cells recapitulate the hierarchal cellular composition of subventricular zone (SVZ), which is comprised of neural stem cells (NSCs), transit amplifying progenitors (TAPs), and neuroblasts. We then derived spheroids from CN which displayed EGFR+/MASH+ TAP and BLBP+ radial glial cell (RGC) characteristic, and mitotic neurogenesis and gliogenesis by single spheroids were observed with cycling multipotential cells. CN-spheroids expressed increased levels of pluripotency and tumor stem cell genes such as KLF4 and TPD5L1, when compared to their differentiated cells and human NSCs. Importantly, Gene Set Enrichment Analysis showed that gene sets of GBM-Spheroids, EGFR Signaling, and Packaging of Telomere Ends are enriched in CN-spheroids in comparison with their differentiated cells. We speculate that CN tumor stem cells have TAP and RGC characteristics, and upregulation of EGFR signaling as well as downregulation of eph-ephrin signaling have critical roles in tumorigenesis of CN. And their ephemeral nature of TAPs destined to neuroblasts, might reflect benign nature of CN.

An Overview of Adult Neurogenesis

Neurogenesis is maintained in the mammalian brain throughout adulthood in two main regions: the subventricular zone (SVZ) of the lateral ventricles and the subgranular zone (SGZ) of the hippocampal dentate gyrus. Adult neurogenesis is a process composed of multiple steps by which neurons are generated from dividing adult neural stem cells and migrate to be integrated into existing neuronal circuits. Alterations in any of these steps impair neurogenesis and may compromise brain function, leading to cognitive impairment and neurodegenerative diseases. Therefore, understanding the cellular and molecular mechanisms that modulate adult neurogenesis is the centre of attention of regenerative research. In this chapter, we review the main properties of the adult neurogenic niches.

Overlapping migratory mechanisms between neural progenitor cells and brain tumor stem cells

Neural stem cells present in the subventricular zone (SVZ), the largest neurogenic niche of the mammalian brain, are able to self-renew as well as generate neural progenitor cells (NPCs). NPCs are highly migratory and traverse the rostral migratory stream (RMS) to the olfactory bulb, where they terminally differentiate into mature interneurons. NPCs from the SVZ are some of the few cells in the CNS that migrate long distances during adulthood. The migratory process of NPCs is highly regulated by intracellular pathway activation and signaling from the surrounding microenvironment. It involves modulation of cell volume, cytoskeletal rearrangement, and isolation from compact extracellular matrix. In malignant brain tumors including high-grade gliomas, there are cells called brain tumor stem cells (BTSCs) with similar stem cell characteristics to NPCs but with uncontrolled cell proliferation and contribute to tumor initiation capacity, tumor progression, invasion, and tumor maintenance. These BTSCs are resistant to chemotherapy and radiotherapy, and their presence is believed to lead to tumor recurrence at distal sites from the original tumor location, principally due to their high migratory capacity. BTSCs are able to invade the brain parenchyma by utilizing many of the migratory mechanisms used by NPCs. However, they have an increased ability to infiltrate the tight brain parenchyma and utilize brain structures such as myelin tracts and blood vessels as migratory paths. In this article, we summarize recent findings on the mechanisms of cellular migration that overlap between NPCs and BTSCs. A better understanding of the intersection between NPCs and BTSCs will to provide a better comprehension of the BTSCs' invasive capacity and the molecular mechanisms that govern their migration and eventually lead to the development of new therapies to improve the prognosis of patients with malignant gliomas.

Blood vessels as a scaffold for neuronal migration

Neurogenesis and angiogenesis share regulatory factors that contribute to the formation of vascular networks and neuronal circuits in the brain. While crosstalk mechanisms between neural stem cells (NSCs) and the vasculature have been extensively investigated, recent studies have provided evidence that blood vessels also play an essential role in neuronal migration in the brain during development and regeneration. The mechanisms of the neuronal migration along blood vessels, referred to as "vascular-guided migration," are now being elucidated. The vascular endothelial cells secrete soluble factors that attract and promote neuronal migration in collaboration with astrocytes that enwrap the blood vessels. In addition, especially in the adult brain, the blood vessels serve as a migration scaffold for adult-born immature neurons generated in the ventricular-subventricular zone (V-SVZ), a germinal zone surrounding the lateral ventricles. The V-SVZ-derived immature neurons use the vascular scaffold to assist their migration toward an injured area after ischemic stroke, and contribute to neuronal regeneration. Here we review the current knowledge about the role of vasculature in neuronal migration and the molecular mechanisms controlling this process. While most of this research has been done in rodents, a comprehensive understanding of vasculature-guided neuronal migration could contribute to new therapeutic approaches for increasing new neurons in the brain after injury.

Lead exposure reduces survival, neuronal determination, and differentiation of P19 stem cells

Lead (Pb) is a teratogen that poses health risks after acute and chronic exposure. Lead is deposited in the bones of adults and is continuously leached into the blood for decades. While this chronic lead exposure can have detrimental effects on adults such as high blood pressure and kidney damage, developing fetuses and young children are particularly vulnerable. During pregnancy, bone-deposited lead is released into the blood at increased rates and can cross the placental barrier, exposing the embryo to the toxin. Embryos exposed to lead display serious developmental and cognitive defects throughout life. Although studies have investigated lead's effect on late-stage embryos, few studies have examined how lead affects stem cell determination and differentiation. For example, it is unknown whether lead is more detrimental to neuronal determination or differentiation of stem cells. We sought to determine the effect of lead on the determination and differentiation of pluripotent embryonic testicular carcinoma (P19) cells into neurons. Our data indicate that lead exposure significantly inhibits the determination of P19 cells to the neuronal lineage by alteration of N-cadherin and Sox2 expression. We also observed that lead significantly alters subsequent neuronal and glial differentiation. Consequently, this research emphasizes the need to reduce public exposure to lead.

Detachment of Chain-Forming Neuroblasts by Fyn-Mediated Control of cell-cell Adhesion in the Postnatal Brain

In the rodent olfactory system, neuroblasts produced in the ventricular-subventricular zone of the postnatal brain migrate tangentially in chain-like cell aggregates toward the olfactory bulb (OB) through the rostral migratory stream (RMS). After reaching the OB, the chains are dissociated and the neuroblasts migrate individually and radially toward their final destination. The cellular and molecular mechanisms controlling cell-cell adhesion during this detachment remain unclear. Here we report that Fyn, a nonreceptor tyrosine kinase, regulates the detachment of neuroblasts from chains in the male and female mouse OB. By performing chemical screening and in vivo loss-of-function and gain-of-function experiments, we found that Fyn promotes somal disengagement from the chains and is involved in neuronal migration from the RMS into the granule cell layer of the OB. Fyn knockdown or Dab1 (disabled-1) deficiency caused p120-catenin to accumulate and adherens junction-like structures to be sustained at the contact sites between neuroblasts. Moreover, a Fyn and N-cadherin double-knockdown experiment indicated that Fyn regulates the N-cadherin-mediated cell adhesion between neuroblasts. These results suggest that the Fyn-mediated control of cell-cell adhesion is critical for the detachment of chain-forming neuroblasts in the postnatal OB.SIGNIFICANCE STATEMENT In the postnatal brain, newly born neurons (neuroblasts) migrate in chain-like cell aggregates toward their destination, where they are dissociated into individual cells and mature. The cellular and molecular mechanisms controlling the detachment of neuroblasts from chains are not understood. Here we show that Fyn, a nonreceptor tyrosine kinase, promotes the somal detachment of neuroblasts from chains, and that this regulation is critical for the efficient migration of neuroblasts to their destination. We further show that Fyn and Dab1 (disabled-1) decrease the cell-cell adhesion between chain-forming neuroblasts, which involves adherens junction-like structures. Our results suggest that Fyn-mediated regulation of the cell-cell adhesion of neuroblasts is critical for their detachment from chains in the postnatal brain.

N-Cadherin Upregulation Promotes the Neurogenic Differentiation of Menstrual Blood-Derived Endometrial Stem Cells

Peripheral nerve injuries are typically caused by either trauma or medical disorders, and recently, stem cell-based therapies have provided a promising treatment approach. Menstrual blood-derived endometrial stem cells (MenSCs) are considered an ideal therapeutic option for peripheral nerve repair due to a noninvasive collection procedure and their high proliferation rate and immunological tolerance. Here, we successfully isolated MenSCs and examined their biological characteristics including their morphology, multipotency, and immunophenotype. Subsequent in vitro studies demonstrated that MenSCs express high levels of neurotrophic factors, such as NT3, NT4, BDNF, and NGF, and are capable of transdifferentiating into glial-like cells under conventional induction conditions. Moreover, upregulation of N-cadherin (N-cad) mRNA and protein expression was observed after neurogenic differentiation. In vivo studies clearly showed that N-cad knockdown via in utero electroporation perturbed the migration and maturation of mouse neural precursor cells (NPCs). Finally, a further transfection assay also confirmed that N-cad upregulation in MenSCs results in the expression of S100. Collectively, our results confirmed the paracrine effect of MenSCs on neuroprotection as well as their potential for transdifferentiation into glial-like cells and demonstrated that N-cad upregulation promotes the neurogenic differentiation of MenSCs, thereby providing support for transgenic MenSC-based therapy for peripheral nerve injury.

Effect of Vitamin D in HN9.10e Embryonic Hippocampal Cells and in Hippocampus from MPTP-Induced Parkinson's Disease Mouse Model

It has long been proven that neurogenesis continues in the adult brains of mammals in the dentatus gyrus of the hippocampus due to the presence of neural stem cells. Although a large number of studies have been carried out to highlight the localization of vitamin D receptor in hippocampus, the expression of vitamin D receptor in neurogenic dentatus gyrus of hippocampus in Parkinson's disease (PD) and the molecular mechanisms triggered by vitamin D underlying the production of differentiated neurons from embryonic cells remain unknown. Thus, we performed a preclinical in vivo study by inducing PD in mice with MPTP and showed a reduction of glial fibrillary acidic protein (GFAP) and vitamin D receptor in the dentatus gyrus of hippocampus. Then, we performed an in vitro study by inducing embryonic hippocampal cell differentiation with vitamin D. Interestingly, vitamin D stimulates the expression of its receptor. Vitamin D receptor is a transcription factor that probably is responsible for the upregulation of microtubule associated protein 2 and neurofilament heavy polypeptide genes. The latter increases heavy neurofilament protein expression, essential for neurofilament growth. Notably N-cadherin, implicated in activity for dendritic outgrowth, is upregulated by vitamin D.

Epb41l5 competes with Delta as a substrate for Mib1 to coordinate specification and differentiation of neurons

We identified Erythrocyte membrane protein band 4.1-like 5 (Epb41l5) as a substrate for the E3 ubiquitin ligase Mind bomb 1 (Mib1), which is essential for activation of Notch signaling. Although loss of Epb41l5 does not significantly alter the pattern of neural progenitor cells (NPCs) specified as neurons at the neural plate stage, it delays their delamination and differentiation after neurulation when NPCs normally acquire organized apical junctional complexes (AJCs) in the zebrafish hindbrain. Delays in differentiation are reduced by knocking down N-cadherin, a manipulation expected to help destabilize adherens junctions (AJs). This suggested that delays in neuronal differentiation in epb41l5-deficient embryos are related to a previously described role for Epb41l5 in facilitating disassembly of cadherin-dependent AJCs. Mib1 ubiquitylates Epb41l5 to promote its degradation. DeltaD can compete with Epb41l5 to reduce Mib1-dependent Epb41l5 degradation. In this context, increasing the number of NPCs specified to become neurons, i.e. cells expressing high levels of DeltaD, stabilizes Epb41l5 in the embryo. Together, these observations suggest that relatively high levels of Delta stabilize Epb41l5 in NPCs specified as neurons. This, we suggest, helps coordinate NPC specification with Epb41l5-dependent delamination and differentiation as neurons.

Physiological electrical signals promote chain migration of neuroblasts by up-regulating P2Y1 purinergic receptors and enhancing cell adhesion

Neuroblasts migrate as directed chains of cells during development and following brain damage. A fuller understanding of the mechanisms driving this will help define its developmental significance and in the refinement of strategies for brain repair using transplanted stem cells. Recently, we reported that in adult mouse there are ionic gradients within the extracellular spaces that create an electrical field (EF) within the rostral migratory stream (RMS), and that this acts as a guidance cue for neuroblast migration. Here, we demonstrate an endogenous EF in brain slices and show that mimicking this by applying an EF of physiological strength, switches on chain migration in mouse neurospheres and in the SH-SY5Y neuroblastoma cell line. Firstly, we detected a substantial endogenous EF of 31.8 ± 4.5 mV/mm using microelectrode recordings from explants of the subventricular zone (SVZ). Pharmacological inhibition of this EF, effectively blocked chain migration in 3D cultures of SVZ explants. To mimic this EF, we applied a physiological EF and found that this increased the expression of N-cadherin and β-catenin, both of which promote cell-cell adhesion. Intriguingly, we found that the EF up-regulated P2Y purinoceptor 1 (P2Y1) to contribute to chain migration of neuroblasts through regulating the expression of N-cadherin, β-catenin and the activation of PKC. Our results indicate that the naturally occurring EF in brain serves as a novel stimulant and directional guidance cue for neuronal chain migration, via up-regulation of P2Y1.

The aged brain: genesis and fate of residual progenitor cells in the subventricular zone

Neural stem cells (NSCs) persist in the adult mammalian brain through life. The subventricular zone (SVZ) is the largest source of stem cells in the nervous system, and continuously generates new neuronal and glial cells involved in brain regeneration. During aging, the germinal potential of the SVZ suffers a widespread decline, but the causes of this turn down are not fully understood. This review provides a compilation of the current knowledge about the age-related changes in the NSC population, as well as the fate of the newly generated cells in the aged brain. It is known that the neurogenic capacity is clearly disrupted during aging, while the production of oligodendroglial cells is not compromised. Interestingly, the human brain seems to primarily preserve the ability to produce new oligodendrocytes instead of neurons, which could be related to the development of neurological disorders. Further studies in this matter are required to improve our understanding and the current strategies for fighting neurological diseases associated with senescence.

Are neural crest stem cells the missing link between hematopoietic and neurogenic niches?

Hematopoietic niches are defined as cellular and molecular microenvironments that regulate hematopoietic stem cell (HSC) function together with stem cell autonomous mechanisms. Many different cell types have been characterized as contributors to the formation of HSC niches, such as osteoblasts, endothelial cells, Schwann cells, and mesenchymal progenitors. These mesenchymal progenitors have themselves been classified as CXC chemokine ligand (CXCL) 12-abundant reticular (CAR) cells, stem cell factor expressing cells, or nestin-positive mesenchymal stem cells (MSCs), which have been recently identified as neural crest-derived cells (NCSCs). Together, these cells are spatially associated with HSCs and believed to provide appropriate microenvironments for HSC self-renewal, differentiation, mobilization and hibernation both by cell-cell contact and soluble factors. Interestingly, it appears that regulatory pathways governing the hematopoietic niche homeostasis are operating in the neurogenic niche as well. Therefore, this review paper aims to compare both the regulation of hematopoietic and neurogenic niches, in order to highlight the role of NCSCs and nervous system components in the development and the regulation of the hematopoietic system.

Potential involvement of kinesin-1 in the regulation of subcellular localization of Girdin

Girdin is an actin-binding protein that has multiple functions in postnatal neural development and cancer progression. We previously showed that Girdin is a regulator of migration for neuroblasts born from neural stem cells in the subventricular zone (SVZ) and the dentate gyrus of the hippocampus in the postnatal brain. Despite a growing list of Girdin-interacting proteins, the mechanism of Girdin-mediated migration has not been fully elucidated. Girdin interacts with Disrupted-In-Schizophrenia 1 and partitioning-defective 3, both of which have been shown to interact with the kinesin microtubule motor proteins. Based on this, we have identified that Girdin also interacts with kinesin-1, a member of neuronal kinesin proteins. Although a direct interaction of Girdin and kinesin-1 has not been determined, it is of interest to find that Girdin loss-of-function mutant mice with the mutation of a basic amino acid residue-rich region (Basic mut mice) exhibit limited interaction with kinesin-1. Furthermore, expression of a kinesin-1 mutant with motor defects, leads to Girdin mislocalization. Finally, consistent with previous studies on the role of kinesin proteins in trafficking a cell-cell adhesion molecule N-cadherin, Basic mut mice showed an aberrant expression pattern of N-cadherin in migrating SVZ neuroblasts. These findings suggest a potential role of Girdin/kinesin-1 interaction in the regulation of neuroblast migration in the postnatal brain.

The role of the microenvironment on the fate of adult stem cells

Adult stem cells (SCs) exist in all tissues that promote tissue growth, regeneration, and healing throughout life. The SC niche in which they reside provides signals that direct them to proliferate, differentiate, or remain dormant; these factors include neighboring cells, the extracellular matrix, soluble molecules, and physical stimuli. In disease and aging states, stable or transitory changes in the microenvironment can directly cause SC activation or inhibition in tissue healing as well as functional regulation. Here, we discuss the microenvironmental regulation of the behavior of SC and focus on plasticity approaches by which various environmental factors can enhance the function of SCs and more effectively direct the fate of SCs.

N-cadherin-based adherens junction regulates the maintenance, proliferation, and differentiation of neural progenitor cells during development

This review addresses our current understanding of the regulatory mechanism by which N-cadherin, a classical cadherin, affects neural progenitor cells (NPCs) during development. N-cadherin is responsible for the integrity of adherens junctions (AJs), which develop in the sub-apical region of NPCs in the neural tube and brain cortex. The apical domain, which contains the sub-apical region, is involved in the switching from symmetric proliferative division to asymmetric neurogenic division of NPCs. In addition, N-cadherin-based AJ is deeply involved in the apico-basal polarity of NPCs and the regulation of Wnt-β-catenin, hedgehog (Hh), and Notch signaling. In this review, we discuss the roles of N-cadherin in the maintenance, proliferation, and differentiation of NPCs through components of AJ, β-catenin and αE-catenin.

Nuclear signaling from cadherin adhesion complexes

The arrival of multicellularity in evolution facilitated cell-cell signaling in conjunction with adhesion. As the ectodomains of cadherins interact with each other directly in trans (as well as in cis), spanning the plasma membrane and associating with multiple other entities, cadherins enable the transduction of "outside-in" or "inside-out" signals. We focus this review on signals that originate from the larger family of cadherins that are inwardly directed to the nucleus, and thus have roles in gene control or nuclear structure-function. The nature of cadherin complexes varies considerably depending on the type of cadherin and its context, and we will address some of these variables for classical cadherins versus other family members. Substantial but still fragmentary progress has been made in understanding the signaling mediators used by varied cadherin complexes to coordinate the state of cell-cell adhesion with gene expression. Evidence that cadherin intracellular binding partners also localize to the nucleus is a major point of interest. In some models, catenins show reduced binding to cadherin cytoplasmic tails favoring their engagement in gene control. When bound, cadherins may serve as stoichiometric competitors of nuclear signals. Cadherins also directly or indirectly affect numerous signaling pathways (e.g., Wnt, receptor tyrosine kinase, Hippo, NFκB, and JAK/STAT), enabling cell-cell contacts to touch upon multiple biological outcomes in embryonic development and tissue homeostasis.

Self administration of oxycodone alters synaptic plasticity gene expression in the hippocampus differentially in male adolescent and adult mice

Abuse and addiction to prescription opioids such as oxycodone (a short-acting Mu opioid receptor (MOP-r) agonist) in adolescence is a pressing public health issue. We have previously shown differences in oxycodone self-administration behaviors between adolescent and adult C57BL/6J mice and expression of striatal neurotransmitter receptor genes, in areas involved in reward. In this study, we aimed to determine whether oxycodone self-administration differentially affects genes regulating synaptic plasticity in the hippocampus of adolescent compared to adult mice, since the hippocampus may be involved in learning aspects associated with chronic drug self administration. Hippocampus was isolated for mRNA analysis from mice that had self administered oxycodone (0.25 mg/kg/infusion) 2h/day for 14 consecutive days or from yoked saline controls. Gene expression was analyzed with real-time polymerase chain reaction (PCR) using a commercially available "synaptic plasticity" PCR array containing 84 genes. We found that adolescent and adult control mice significantly differed in the expression of several genes in the absence of oxycodone exposure, including those coding for mitogen-activated protein kinase, calcium/calmodulin-dependent protein kinase II gamma subunit, glutamate receptor, ionotropic AMPA2 and metabotropic 5. Chronic oxycodone self administration increased proviral integration site 1 (Pim1) and thymoma viral proto-oncogene 1 mRNA levels compared to controls in both age groups. Both Pim1 and cadherin 2 mRNAs showed a significant combined effect of Drug Condition and Age × Drug Condition. Furthermore, the mRNA levels of both cadherin 2 and cAMP response element modulators showed an experiment-wise significant difference between oxycodone and saline control in adult but not in adolescent mice. Overall, this study demonstrates for the first time that chronic oxycodone self-administration differentially alters synaptic plasticity gene expression in the hippocampus of adolescent and adult mice.

Site-specific differentiation of neural stem cell regulated by micropatterned multicomponent interfaces

Stem cell microenvironments are enriched by signals from a variety of components, which cooperate spatially and temporally to regulate cellular function. In vitro recapitulating such complexity in a well-controlled manner is elusive. Here, a platform for patterning multiple bio-active proteins on a single substrate is developed and optimized, and is used it to study the cooperative involvement of cell-matrix interaction and cell-cell signaling in regulating neural stem cell (NSC) function. An affinity-capturing-based multi-step microcontact printing is used to pattern, extracellular matrix proteins, and cell-cell signaling ligands, as intersecting lines on a nonadhesive background. Such design provides spatial segregation of signals from different extrinsic components, while allowing cell traffic between them during their proliferation and differentiation processes. Rat embryonic neural stem cells are cultured and characterized on the multicomponent substrates patterned with different combinations of fibronectin, N-cadherin, and Jagged1 proteins and allow to proliferate and differentiate over long term. It is found that local presentation of Notch signaling ligand (Jagged1) or cell adhesion molecule (N-cadherin) effectively modulate the balance between cell-cell and cell-matrix interaction, and significantly change the overall spatial remodeling of NSC differentiation. This platform provides an unambiguous approach to study the spatial and temporal cooperative involvement of different extrinsic components in regulating stem cell behavior. It is also readily expandable for inclusion of extra components and applicable to use with other types of cells, which provide a powerful tool for basic study of cell-material interaction or advanced tissue-interface engineering.

RalA promotes a direct exocyst-Par6 interaction to regulate polarity in neuronal development

Cell polarization is essential for neuronal development in both the embryonic and postnatal brain. Here, using primary cultures, in vivo postnatal electroporation and conditional genetic ablation, we show that the Ras-like small GTPase RalA and its effector, the exocyst, regulate the morphology and polarized migration of neural progenitors derived from the subventricular zone, a major neurogenic niche in the postnatal brain. Active RalA promotes the direct binding between the exocyst subunit Exo84 and the PDZ domain of Par6 through a non-canonical PDZ-binding motif. Blocking the Exo84-Par6 interaction impairs polarization in postnatal neural progenitors and cultured embryonic neurons. Our results provide the first in vivo characterization of RalA function in the mammalian brain and highlight a novel molecular mechanism for cell polarization. Given that the exocyst and the Par complex are conserved in many tissues, the functional significance of their interaction and its regulation by RalA are likely to be important in a wide range of polarization events.

Regulation of cadherin expression in nervous system development

This review addresses our current understanding of the regulatory mechanisms for classical cadherin expression during development of the vertebrate nervous system. The complexity of the spatial and temporal expression patterns is linked to morphogenic and functional roles in the developing nervous system. While the regulatory networks controlling cadherin expression are not well understood, it is likely that the multiple signaling pathways active in the development of particular domains also regulate the specific cadherins expressed at that time and location. With the growing understanding of the broader roles of cadherins in cell-cell adhesion and non-adhesion processes, it is important to understand both the upstream regulation of cadherin expression and the downstream effects of specific cadherins within their cellular context.

WNT signaling increases proliferation and impairs differentiation of stem cells in the developing cerebellum

The WNT pathway plays multiple roles in neural development and is crucial for establishment of the embryonic cerebellum. In addition, WNT pathway mutations are associated with medulloblastoma, the most common malignant brain tumor in children. However, the cell types within the cerebellum that are responsive to WNT signaling remain unknown. Here we investigate the effects of canonical WNT signaling on two important classes of progenitors in the developing cerebellum: multipotent neural stem cells (NSCs) and granule neuron precursors (GNPs). We show that WNT pathway activation in vitro promotes proliferation of NSCs but not GNPs. Moreover, mice that express activated β-catenin in the cerebellar ventricular zone exhibit increased proliferation of NSCs in that region, whereas expression of the same protein in GNPs impairs proliferation. Although β-catenin-expressing NSCs proliferate they do not undergo prolonged expansion or neoplastic growth; rather, WNT signaling markedly interferes with their capacity for self-renewal and differentiation. At a molecular level, mutant NSCs exhibit increased expression of c-Myc, which might account for their transient proliferation, but also express high levels of bone morphogenetic proteins and the cyclin-dependent kinase inhibitor p21, which might contribute to their altered self-renewal and differentiation. These studies suggest that the WNT pathway is a potent regulator of cerebellar stem cell growth and differentiation.

Adherens junctions and stem cells

The specification, maintenance, division and differentiation of stem cells are integral to the development and homeostasis of many tissues. These stem cells often live in specialized anatomical areas, called niches. While niches can be complex, most involve cell-cell interactions that are mediated by adherens junctions. A diverse array of functions have been attributed to adherens junctions in stem cell biology. These include physical anchoring to the niche, control of proliferation and division orientation, regulation of signaling cascades and of differentiation. In this review, a number of model stem cell systems that highlight various functions of adherens junctions are discussed. In addition, a summary of the current understanding of adherens junction function in mammalian tissues and embryonic and induced pluripotent stem cells is provided. This analysis demonstrates that the roles of adherens junctions are surprisingly varied and integrated with both the anatomy and the physiology of the tissue.

Ion channels and ionotropic receptors in human embryonic stem cell derived neural progenitors

Human neural progenitor cells differentiated from human embryonic stem cells offer a potential cell source for studying neurodegenerative diseases and for drug screening assays. Previously, we demonstrated that human neural progenitors could be maintained in a proliferative state with the addition of leukemia inhibitory factor and basic fibroblast growth factor. Here we demonstrate that 96 h after removal of basic fibroblast growth factor the neural progenitor cell culture was significantly altered and cell replication halted. Fourteen days after the removal of basic fibroblast growth factor, most cells expressed microtubule-associated protein 2 and TUJ1, markers characterizing a post-mitotic neuronal phenotype as well as neural developmental markers Cdh2 and Gbx2. Real-time PCR was performed to determine the ionotropic receptor subunit expression profile. Differentiated neural progenitors express subunits of glutamatergic, GABAergic, nicotinic, purinergic and transient receptor potential receptors. In addition, sodium and calcium channel subunits were also expressed. Functionally, virtually all the hNP cells tested under whole-cell voltage clamp exhibited delayed rectifier potassium channel currents and some differentiated cells exhibited tetrodotoxin-sensitive, voltage-dependent sodium channel current. Action potentials could also be elicited by currents injection under whole-cell current clamp in a minority of cells. These results indicate that removing basic fibroblast growth factor from the neural progenitor cell cultures leads to a post-mitotic state, and has the capability to produce excitable cells that can generate action potentials, a landmark characteristic of a neuronal phenotype. This is the first report of an efficient and simple means of generating human neuronal cells for ionotropic receptor assays and ultimately for electrically active human neural cell assays for drug discovery.