NeuroD2 and neuroD3: distinct expression patterns and transcriptional activation potentials within the neuroD gene family

Exploring the Functional Heterogeneity of Directly Reprogrammed Neural Stem Cell-Derived Neurons via Single-Cell RNA Sequencing

The therapeutic potential of directly reprogrammed neural stem cells (iNSCs) for neurodegenerative diseases relies on reducing the innate tumorigenicity of pluripotent stem cells. However, the heterogeneity within iNSCs is a major hurdle in quality control prior to clinical applications. Herein, we generated iNSCs from human fibroblasts, by transfecting transcription factors using Sendai virus particles, and characterized the expression of iNSC markers. Using immunostaining and quantitative real time -polymerase chain reaction (RT -qPCR), no differences were observed between colonies of iNSCs and iNSC-derived neurons. Unexpectedly, patch-clamp analysis of iNSC-derived neurons revealed distinctive action potential firing even within the same batch product. We performed single-cell RNA sequencing in fibroblasts, iNSCs, and iNSC-derived neurons to dissect their functional heterogeneity and identify cell fate regulators during direct reprogramming followed by neuronal differentiation. Pseudotime trajectory analysis revealed distinct cell types depending on their gene expression profiles. Differential gene expression analysis showed distinct NEUROG1, PEG3, and STMN2 expression patterns in iNSCs and iNSC-derived neurons. Taken together, we recommend performing a predictable functional assessment with appropriate surrogate markers to ensure the quality control of iNSCs and their differentiated neurons, particularly before cell banking for regenerative cell therapy.

Analysis of medaka GAP43 gene promoter activity in transgenic lines

We produced transgenic medaka fish lines that mimicked the expression of the GAP43 gene. Fish lines with the proximal 2-kilobase (kb) 5'-untranslated region (UTR) as the expression promoter specifically expressed enhanced green fluorescent protein (EGFP) in neural tissues, such as the brain, spinal cord, and peripheral nerves, and its expression decreased with growth, but persisted until adulthood. A functional analysis of the promoter using partially deleted UTRs revealed that functions related to neural tissue-specific promoter activity were widely distributed in the region upstream of the proximal 400-b. Furthermore, the distal half of the 2-kb UTR contributed to expression throughout the brain, while the region 400-b upstream of the proximal 600-b was strongly associated with expression in specific areas, such as the telencephalon. In addition, a region from 957 to 557 b upstream of the translation initiation site was important for the long-term maintenance of promoter activity into adulthood. Among the transcription factors with recognition sequences in this region, Sp1 and CREB1 have been suggested to play important roles in the GAP43 promoter expression characteristics, such as strong expression in the telencephalon and long-term maintenance of expression.

Disruption of NEUROD2 causes a neurodevelopmental syndrome with autistic features via cell-autonomous defects in forebrain glutamatergic neurons

While the transcription factor NEUROD2 has recently been associated with epilepsy, its precise role during nervous system development remains unclear. Using a multi-scale approach, we set out to understand how Neurod2 deletion affects the development of the cerebral cortex in mice. In Neurod2 KO embryos, cortical projection neurons over-migrated, thereby altering the final size and position of layers. In juvenile and adults, spine density and turnover were dysregulated in apical but not basal compartments in layer 5 neurons. Patch-clamp recordings in layer 5 neurons of juvenile mice revealed increased intrinsic excitability. Bulk RNA sequencing showed dysregulated expression of many genes associated with neuronal excitability and synaptic function, whose human orthologs were strongly associated with autism spectrum disorders (ASD). At the behavior level, Neurod2 KO mice displayed social interaction deficits, stereotypies, hyperactivity, and occasionally spontaneous seizures. Mice heterozygous for Neurod2 had similar defects, indicating that Neurod2 is haploinsufficient. Finally, specific deletion of Neurod2 in forebrain excitatory neurons recapitulated cellular and behavioral phenotypes found in constitutive KO mice, revealing the region-specific contribution of dysfunctional Neurod2 in symptoms. Informed by these neurobehavioral features in mouse mutants, we identified eleven patients from eight families with a neurodevelopmental disorder including intellectual disability and ASD associated with NEUROD2 pathogenic mutations. Our findings demonstrate crucial roles for Neurod2 in neocortical development, whose alterations can cause neurodevelopmental disorders including intellectual disability and ASD.

The Rise of Molecules Able To Regenerate the Central Nervous System

Injury to the adult central nervous system (CNS) usually leads to permanent deficits of cognitive, sensory, and/or motor functions. The failure of axonal regeneration in the damaged CNS limits functional recovery. The lack of information concerning the biological mechanism of axonal regeneration and its complexity has delayed the process of drug discovery for many years compared to other drug classes. Starting in the early 2000s, the ability of many molecules to stimulate axonal regrowth was evaluated through automated screening techniques; many hits and some new mechanisms involved in axonal regeneration were identified. In this Perspective, we discuss the rise of the CNS regenerative drugs, the main biological techniques used to test these drug candidates, some of the most important screens performed so far, and the main challenges following the identification of a drug that is able to induce axonal regeneration in vivo.

Atoh1 Controls Primary Cilia Formation to Allow for SHH-Triggered Granule Neuron Progenitor Proliferation

During cerebellar development, granule neuron progenitors (GNPs) proliferate by transducing Sonic Hedgehog (SHH) signaling via the primary cilium. Precise regulation of ciliogenesis, thus, ensures proper GNP pool expansion. Here, we report that Atoh1, a transcription factor required for GNPs formation, controls the presence of primary cilia, maintaining GNPs responsiveness to SHH. Loss of primary cilia abolishes the ability of Atoh1 to keep GNPs in a proliferative state. Mechanistically, Atoh1 promotes ciliogenesis by transcriptionally regulating Cep131, which facilitates centriolar satellite (CS) clustering to the basal body. Importantly, ectopic expression of Cep131 counteracts the effects of Atoh1 loss in GNPs by restoring proper localization of CS and ciliogenesis. This Atoh1-CS-primary cilium-SHH pro-proliferative pathway is also conserved in SHH-type medulloblastoma, a pediatric brain tumor arising from the GNPs. Together, our data reveal how Atoh1 modulates the primary cilium to regulate GNPs development.

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.

De novo pathogenic variants in neuronal differentiation factor 2 (NEUROD2) cause a form of early infantile epileptic encephalopathy

BACKGROUND

Early infantile epileptic encephalopathies are severe disorders consisting of early-onset refractory seizures accompanied often by significant developmental delay. The increasing availability of next-generation sequencing has facilitated the recognition of single gene mutations as an underlying aetiology of some forms of early infantile epileptic encephalopathies.

OBJECTIVES

This study was designed to identify candidate genes as a potential cause of early infantile epileptic encephalopathy, and then to provide genetic and functional evidence supporting patient variants as causative.

METHODS

We used whole exome sequencing to identify candidate genes. To model the disease and assess the functional effects of patient variants on candidate protein function, we used in vivo CRISPR/Cas9-mediated genome editing and protein overexpression in frog tadpoles.

RESULTS

We identified novel de novo variants in neuronal differentiation factor 2 (NEUROD2) in two unrelated children with early infantile epileptic encephalopathy. Depleting neurod2 with CRISPR/Cas9-mediated genome editing induced spontaneous seizures in tadpoles, mimicking the patients' condition. Overexpression of wild-type NEUROD2 induced ectopic neurons in tadpoles; however, patient variants were markedly less effective, suggesting that both variants are dysfunctional and likely pathogenic.

CONCLUSION

This study provides clinical and functional support for NEUROD2 variants as a cause of early infantile epileptic encephalopathy, the first evidence of human disease caused by NEUROD2 variants.

The transcription factor NeuroD2 coordinates synaptic innervation and cell intrinsic properties to control excitability of cortical pyramidal neurons

KEY POINTS

Synaptic excitation and inhibition must be properly balanced in individual neurons and neuronal networks to allow proper brain function. Disrupting this balance may lead to autism spectral disorders and epilepsy. We show the basic helix-loop-helix transcription factor NeuroD2 promotes inhibitory synaptic drive but also decreases cell-intrinsic neuronal excitability of cortical pyramidal neurons both in vitro and in vivo. We identify two genes potentially downstream of NeuroD2-mediated transcription that regulate these parameters: gastrin-releasing peptide and the small conductance, calcium-activated potassium channel, SK2. Our results reveal an important function for NeuroD2 in balancing synaptic neurotransmission and intrinsic excitability. Our results offer insight into how synaptic innervation and intrinsic excitability are coordinated during cortical development.

ABSTRACT

Synaptic excitation and inhibition must be properly balanced in individual neurons and neuronal networks for proper brain function. Disruption of this balance during development may lead to autism spectral disorders and epilepsy. Synaptic excitation is counterbalanced by synaptic inhibition but also by attenuation of cell-intrinsic neuronal excitability. To maintain proper excitation levels during development, neurons must sense activity over time and regulate the expression of genes that control these parameters. While this is a critical process, little is known about the transcription factors involved in coordinating gene expression to control excitatory/inhibitory synaptic balance. We show here that the basic helix-loop-helix transcription factor NeuroD2 promotes inhibitory synaptic drive but also decreases cell-intrinsic neuronal excitability of cortical pyramidal neurons both in vitro and in vivo as shown by ex vivo analysis of a NeuroD2 knockout mouse. Using microarray analysis and comparing wild-type and NeuroD2 knockout cortical networks, we identified two potential gene targets of NeuroD2 that contribute to these processes: gastrin-releasing peptide (GRP) and the small conductance, calcium-activated potassium channel, SK2. We found that the GRP receptor antagonist RC-3059 and the SK2 specific blocker apamin partially reversed the effects of increased NeuroD2 expression on inhibitory synaptic drive and action potential repolarization, respectively. Our results reveal an important function for NeuroD2 in balancing synaptic neurotransmission and intrinsic excitability and offer insight into how these processes are coordinated during cortical development.

Terminal Differentiation of Adult Hippocampal Progenitor Cells Is a Step Functionally Dissociable from Proliferation and Is Controlled by Tis21, Id3 and NeuroD2

Cell proliferation and differentiation are interdependent processes. Here, we have asked to what extent the two processes of neural progenitor cell amplification and differentiation are functionally separated. Thus, we analyzed whether it is possible to rescue a defect of terminal differentiation in progenitor cells of the dentate gyrus, where new neurons are generated throughout life, by inducing their proliferation and/or their differentiation with different stimuli appropriately timed. As a model we used the Tis21 knockout mouse, whose dentate gyrus neurons, as demonstrated by us and others, have an intrinsic defect of terminal differentiation. We first tested the effect of two proliferative as well as differentiative neurogenic stimuli, one pharmacological (fluoxetine), the other cognitive (the Morris water maze (MWM) training). Both effectively enhanced the number of new dentate gyrus neurons produced, and fluoxetine also reduced the S-phase length of Tis21 knockout dentate gyrus progenitor cells and increased the rate of differentiation of control cells, but neither factor enhanced the defective rate of differentiation. In contrast, the defect of terminal differentiation was fully rescued by in vivo infection of proliferating dentate gyrus progenitor cells with retroviruses either silencing Id3, an inhibitor of neural differentiation, or expressing NeuroD2, a proneural gene expressed in terminally differentiated dentate gyrus neurons. This is the first demonstration that NeuroD2 or the silencing of Id3 can activate the differentiation of dentate gyrus neurons, complementing a defect of differentiation. It also highlights how the rate of differentiation of dentate gyrus neurons is regulated genetically at several levels and that a neurogenic stimulus for amplification of neural stem/progenitor cells may not be sufficient in itself to modify this rate.

Associations of NEUROD2 polymorphisms and change of cognitive dysfunctions in schizophrenia and schizoaffective disorder after eight weeks of antipsychotic treatment

INTRODUCTION

NEUROD2 is a neurospecific helix-loop-helix transcription factor which has an impact on the regulation of glutamatergic and GABAergic genes. We investigated an association of NEUROD2 with neurocognitive dysfunctions in schizophrenia and schizoaffective disorder patients before and during treatment with different second-generation antipsychotics.

METHODS

Patients were genotyped for four different polymorphisms of the NEUROD2 gene ((rs9889354(A/G), rs1877032(C/T), rs12453682(C/T) and rs11078918(C/G)). Cognitive function was assessed at baseline and week 8. Results of individual neuropsychological tests were assigned to six cognitive domains (reaction time and quality; executive function; working, verbal and visual memory) and a general cognitive index.

RESULTS

167 patients were included in the study. The NEUROD2 exonic polymorphism rs11078918 showed significant associations with verbal memory and executive functions, whereas the NEUROD2 polymorphism rs12453682 was significantly associated with working and verbal memory, executive functions and with a cognitive index. Significant associations were found at baseline and after eight weeks. Moreover, significant associations between the change in neuropsychological test results during antipsychotic treatment and the NEUROD2 polymorphisms rs11078918 and rs12453682 were observed.

CONCLUSIONS

Our findings suggest that the NEUROD2 gene could play a role in the pathophysiology of neurocognitive dysfunctions as well as in the change of cognitive symptoms under antipsychotic treatment in schizophrenia and schizoaffective disorder.

NEUROD2 Regulates Stim1 Expression and Store-Operated Calcium Entry in Cortical Neurons

Calcium signaling controls many key processes in neurons, including gene expression, axon guidance, and synaptic plasticity. In contrast to calcium influx through voltage- or neurotransmitter-gated channels, regulatory pathways that control store-operated calcium entry (SOCE) in neurons are poorly understood. Here, we report a transcriptional control of Stim1 (stromal interaction molecule 1) gene, which is a major sensor of endoplasmic reticulum (ER) calcium levels and a regulator of SOCE. By using a genome-wide chromatin immunoprecipitation and sequencing approach in mice, we find that NEUROD2, a neurogenic transcription factor, binds to an intronic element within the Stim1 gene. We show that NEUROD2 limits Stim1 expression in cortical neurons and consequently fine-tunes the SOCE response upon depletion of ER calcium. Our findings reveal a novel mechanism that regulates neuronal calcium homeostasis during cortical development.

Discovery, Optimization, and Biological Evaluation of Sulfonamidoacetamides as an Inducer of Axon Regeneration

Axon regeneration after injury in the central nervous system is hampered in part because if an age-dependent decline in the intrinsic axon growth potential, and one of the strategies to stimulate axon growth in injured neurons involves pharmacological manipulation of implicated signaling pathways. Here we report phenotypic cell-based screen of chemical libraries and structure-activity-guided optimization that resulted in the identification of compound 7p which promotes neurite outgrowth of cultured primary neurons derived from the hippocampus, cerebral cortex, and retina. In an animal model of optic nerve injury, compound 7p was shown to induce growth of GAP-43 positive axons, indicating that the in vitro neurite outgrowth activity of compound 7p translates into stimulation of axon regeneration in vivo. Further optimization of compound 7p and elucidation of the mechanisms by which it elicits axon regeneration in vivo will provide a rational basis for future efforts to enhance treatment strategies.

Micropatterning Extracellular Matrix Proteins on Electrospun Fibrous Substrate Promote Human Mesenchymal Stem Cell Differentiation Toward Neurogenic Lineage

In this study, hybrid micropatterned grafts constructed via a combination of microcontact printing and electrospinning techniques process were utilized to investigate the influencing of patterning directions on human mesenchymal stem cells (hMSCs) differentiation to desired phenotypes. We found that the stem cells could align and elongate along the direction of the micropattern, where they randomly distributed on nonmicropatterned surfaces. Concomitant with patterning effect of component on stem cell alignment, a commensurate increase on the expression of neural lineage commitment markers, such as microtubule associated protein 2 (MAP2), Nestin, NeuroD1, and Class III β-Tubulin, were revealed from mRNA expression by quantitative Real Time PCR (qRT-PCR) and MAP2 expression by immunostaining. In addition, the effect of electrospun fiber orientation on cell behaviors was further examined. An angle of 45° between the direction of micropatterning and orientation of aligned fibers was verified to greatly prompt the outgrowth of filopodia and neurogenesis of hMSCs. This study demonstrates that the significance of hybrid components and electrospun fiber alignment in modulating cellular behavior and neurogenic lineage commitment of hMSCs, suggesting promising application of porous scaffolds with smart component and topography engineering in clinical regenerative medicine.

Genome-wide target analysis of NEUROD2 provides new insights into regulation of cortical projection neuron migration and differentiation

Background

Cellular differentiation programs are controlled, to a large extent, by the combinatorial functioning of specific transcription factors. Cortical projection neurons constitute the major excitatory neuron population within the cortex and mediate long distance communication between the cortex and other brain regions. Our understanding of effector transcription factors and their downstream transcriptional programs that direct the differentiation process of cortical projection neurons is far from complete.

Results

In this study, we carried out a ChIP-Seq (chromatin-immunoprecipitation and sequencing) analysis of NEUROD2, an effector transcription factor expressed in lineages of cortical projection neurons during the peak of cortical excitatory neurogenesis. Our results suggest that during cortical development NEUROD2 targets key genes that are required for Reelin signaling, a major pathway that regulates the migration of neurons from germinal zones to their final layers of residence within the cortex. We also find that NEUROD2 binds to a large set of genes with functions in layer-specific differentiation and in axonal pathfinding of cortical projection neurons.

Conclusions

Our analysis of in vivo NEUROD2 target genes offers mechanistic insight into signaling pathways that regulate neuronal migration and axon guidance and identifies genes that are likely to be required for proper cortical development.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1882-9) contains supplementary material, which is available to authorized users.

The Role of Atonal Factors in Mechanosensory Cell Specification and Function

Atonal genes are basic helix-loop-helix transcription factors that were first identified as regulating the formation of mechanoreceptors and photoreceptors in Drosophila. Isolation of vertebrate homologs of atonal genes has shown these transcription factors to play diverse roles in the development of neurons and their progenitors, gut epithelial cells, and mechanosensory cells in the inner ear and skin. In this article, we review the molecular function and regulation of atonal genes and their targets, with particular emphasis on the function of Atoh1 in the development, survival, and function of hair cells of the inner ear. We discuss cell-extrinsic signals that induce Atoh1 expression and the transcriptional networks that regulate its expression during development. Finally, we discuss recent work showing how identification of Atoh1 target genes in the cerebellum, spinal cord, and gut can be used to propose candidate Atoh1 targets in tissues such as the inner ear where cell numbers and biochemical material are limiting.

T-cell TGF-β signaling abrogation restricts medulloblastoma progression

Cancer cell secretion of TGF-β is a potent mechanism for immune evasion. However, little is known about how central nervous system tumors guard against immune eradication. We sought to determine the impact of T-cell TGF-β signaling blockade on progression of medulloblastoma (MB), the most common pediatric brain tumor. Genetic abrogation of T-cell TGF-β signaling mitigated tumor progression in the smoothened A1 (SmoA1) transgenic MB mouse. T regulatory cells were nearly abolished and antitumor immunity was mediated by CD8 cytotoxic T lymphocytes. To define the CD8 T-cell subpopulation responsible, primed CD8 T cells were adoptively transferred into tumor-bearing immunocompromised SmoA1 recipients. This led to generation of CD8(+)/killer cell lectin-like receptor G1 high (KLRG1(hi))/IL-7R(lo) short-lived effector cells that expressed granzyme B at the tumor. These results identify a cellular immune mechanism whereby TGF-β signaling blockade licenses the T-cell repertoire to kill pediatric brain tumor cells.

Skeletal muscle programming and re-programming

The discovery of the transcription factor MyoD and its ability to induce muscle differentiation was the first demonstration of genetically programmed cell transdifferentiation. MyoD functions by activating a feed-forward circuit to regulate muscle gene expression. This requires binding to specific E-boxes throughout the genome, followed by recruitment of chromatin modifying complexes and transcription machinery. MyoD binding can be modified by both cooperative factors and inhibitors, including microRNAs that may serve as important developmental switches. Recent studies indicate that epigenetic regulation of MyoD binding sites is another important mechanism for controlling MyoD activity, which may ultimately limit its ability to induce transdifferentiation to cells with permissive epigenetic 'landscapes.'

NeuroD modulates opioid agonist-selective regulation of adult neurogenesis and contextual memory extinction

Addictive drugs, including opioids, modulate adult neurogenesis. In order to delineate the probable implications of neurogenesis on contextual memory associated with addiction, we investigated opioid agonist-selective regulation of neurogenic differentiation 1 (NeuroD) activities under the conditioned place preference (CPP) paradigm. Training mice with equivalent doses of morphine and fentanyl produced different CPP extinction rates without measurable differences in the CPP acquisition rate or magnitude. Fentanyl-induced CPP required much longer time for extinction than morphine-induced CPP. We observed a parallel decrease in NeuroD activities and neurogenesis after morphine-induced CPP, but not after fentanyl-induced CPP. Increasing NeuroD activities with NeuroD-lentivirus (nd-vir) injection at the dentate gyrus before CPP training reversed morphine-induced decreases in NeuroD activities and neurogenesis, and prolonged the time required for extinction of morphine-induced CPP. On the other hand, decreasing NeuroD activities via injection of miRNA-190-virus (190-vir) reversed the fentanyl effect on NeuroD and neurogenesis and shortened the time required for extinction of fentanyl-induced CPP. Another contextual memory task, the Morris Water Maze (MWM), was affected similarly by alteration of NeuroD activities. The reduction in NeuroD activities either by morphine treatment or 190-vir injection decreased MWM task retention, while the increase in NeuroD activities by nd-vir prolonged MWM task retention. Thus, by controlling NeuroD activities, opioid agonists differentially regulate adult neurogenesis and subsequent contextual memory retention. Such drug-related memory regulation could have implications in eventual context-associated relapse.

Inducible and conditional deletion of extracellular signal-regulated kinase 5 disrupts adult hippocampal neurogenesis

Recent studies have led to the exciting idea that adult-born neurons in the dentate gyrus of the hippocampus may play a role in hippocampus-dependent memory formation. However, signaling mechanisms that regulate adult hippocampal neurogenesis are not well defined. Here we report that extracellular signal-regulated kinase 5 (ERK5), a member of the mitogen-activated protein kinase family, is selectively expressed in the neurogenic regions of the adult mouse brain. We present evidence that shRNA suppression of ERK5 in adult hippocampal neural stem/progenitor cells (aNPCs) reduces the number of neurons while increasing the number of cells expressing markers for stem/progenitor cells or proliferation. Furthermore, shERK5 attenuates both transcription and neuronal differentiation mediated by Neurogenin 2, a transcription factor expressed in adult hippocampal neural progenitor cells. By contrast, ectopic activation of endogenous ERK5 signaling via expression of constitutive active MEK5, an upstream activating kinase for ERK5, promotes neurogenesis in cultured aNPCs and in the dentate gyrus of the mouse brain. Moreover, neurotrophins including NT3 activate ERK5 and stimulate neuronal differentiation in aNPCs in an ERK5-dependent manner. Finally, inducible and conditional deletion of ERK5 specifically in the neurogenic regions of the adult mouse brain delays the normal progression of neuronal differentiation and attenuates adult neurogenesis in vivo. These data suggest ERK5 signaling as a critical regulator of adult hippocampal neurogenesis.

NeuroD2 regulates the development of hippocampal mossy fiber synapses

BACKGROUND

The assembly of neural circuits requires the concerted action of both genetically determined and activity-dependent mechanisms. Calcium-regulated transcription may link these processes, but the influence of specific transcription factors on the differentiation of synapse-specific properties is poorly understood. Here we characterize the influence of NeuroD2, a calcium-dependent transcription factor, in regulating the structural and functional maturation of the hippocampal mossy fiber (MF) synapse.

RESULTS

Using NeuroD2 null mice and in vivo lentivirus-mediated gene knockdown, we demonstrate a critical role for NeuroD2 in the formation of CA3 dendritic spines receiving MF inputs. We also use electrophysiological recordings from CA3 neurons while stimulating MF axons to show that NeuroD2 regulates the differentiation of functional properties at the MF synapse. Finally, we find that NeuroD2 regulates PSD95 expression in hippocampal neurons and that PSD95 loss of function in vivo reproduces CA3 neuron spine defects observed in NeuroD2 null mice.

CONCLUSION

These experiments identify NeuroD2 as a key transcription factor that regulates the structural and functional differentiation of MF synapses in vivo.

Induction of neural differentiation by the transcription factor neuroD2

Pro-neural basic helix loop helix (bHLH) transcription factors are involved in many aspects of normal neuronal development, and over-expression of genes for several of these factors has been shown to induce aspects of neuronal differentiation in cell lines and stem cells. Here we show that over-expression of NeuroD2 (ND2), Neurogenin1 and 2 leads to morphological differentiation of N18-RE-105 neuroblastoma cells and increased expression of synaptic proteins. Particularly ND2 induced neurite formation and increases in the expression of synaptic proteins such as synaptotagmin, that is not expressed normally in this cell type, as well as the redistribution of another synaptic protein, SNAP25, to a cell membrane location. Infection of human neural progenitor cells using adeno associated viral (AAV) vectors also promoted neuronal differentiation. Over-expressing cells demonstrated a significant increase in the neuron specific form of tubulin as well as increased expression of synaptotagmin. Genetic modification of neural progenitor cell with bHLH factors such as ND2 may be a viable strategy to enhance differentiation of these cells into replacement neurons for human disease.

MicroRNA-mediated conversion of human fibroblasts to neurons

Neurogenic transcription factors and evolutionarily conserved signalling pathways have been found to be instrumental in the formation of neurons. However, the instructive role of microRNAs (miRNAs) in neurogenesis remains unexplored. We recently discovered that miR-9* and miR-124 instruct compositional changes of SWI/SNF-like BAF chromatin-remodelling complexes, a process important for neuronal differentiation and function. Nearing mitotic exit of neural progenitors, miR-9* and miR-124 repress the BAF53a subunit of the neural-progenitor (np)BAF chromatin-remodelling complex. After mitotic exit, BAF53a is replaced by BAF53b, and BAF45a by BAF45b and BAF45c, which are then incorporated into neuron-specific (n)BAF complexes essential for post-mitotic functions. Because miR-9/9* and miR-124 also control multiple genes regulating neuronal differentiation and function, we proposed that these miRNAs might contribute to neuronal fates. Here we show that expression of miR-9/9* and miR-124 (miR-9/9*-124) in human fibroblasts induces their conversion into neurons, a process facilitated by NEUROD2. Further addition of neurogenic transcription factors ASCL1 and MYT1L enhances the rate of conversion and the maturation of the converted neurons, whereas expression of these transcription factors alone without miR-9/9*-124 was ineffective. These studies indicate that the genetic circuitry involving miR-9/9*-124 can have an instructive role in neural fate determination.

Transcriptional regulatory regions of gap43 needed in developing and regenerating retinal ganglion cells

Mammals and fish differ in their ability to express axon growth-associated genes in response to CNS injury, which contributes to the differences in their ability for CNS regeneration. Previously we demonstrated that for the axon growth-associated gene, gap43, regions of the rat promoter that are sufficient to promote reporter gene expression in the developing zebrafish nervous system are not sufficient to promote expression in regenerating retinal ganglion cells in zebrafish. Recently, we identified a 3.6-kb gap43 promoter fragment from the pufferfish, Takifugu rubripes (fugu), that can promote reporter gene expression during both development and regeneration. Using promoter deletion analysis, we have found regions of the 3.6-kb fugu gap43 promoter that are necessary for expression in regenerating, but not developing, retinal ganglion cells. Within the 3.6-kb promoter, we have identified elements that are highly conserved among fish, as well as elements conserved among fish, mammals, and birds.

Transcriptional inhibition of REST by NeuroD2 during neuronal differentiation

For a progenitor cell to become a neuron, three activities must occur: neuronal differentiation program must be activated, elements repressing neuronal differentiation must be deactivated and competing differentiation programs must be silenced. It is known that NeuroD2 and related bHLH transcription factors induce neuronal differentiation, REST represses neuronal differentiation, and Zfhx1a prevents myogenic gene expression. We demonstrate that NeuroD2 suppresses REST during differentiation in culture. In the hippocampus of NeuroD2 knockout mice, higher level of REST is detected. Functional significance of NeuroD2-REST interplay is uncovered by showing that forced expression of REST interferes with neuronal differentiation in culture. NeuroD2 inhibits REST indirectly by involving the inhibitor of myogenic genes, Zfhx1a, which binds response elements in REST 5'-UTR. Our study supports a model wherein NeuroD2 induces transcription of neuronal genes and Zfhx1a, which in turn de-represses neuronal differentiation by down-regulating REST, and suppresses competing myogenic fate.

Micropatterned matrix directs differentiation of human mesenchymal stem cells towards myocardial lineage

Stem cell response can be influenced by a multitude of chemical, topological and mechanical physiochemical cues. While extensive studies have been focused on the use of soluble factors to direct stem cell differentiation, there are growing evidences illustrating the potential to modulate stem cell differentiation via precise engineering of cell shape. Fibronectin were printed on poly(lactic-co-glycolic acid) (PLGA) thin film forming spatially defined geometries as a means to control the morphology of bone marrow derived human mesenchymal stem cells (hMSCs). hMSCs that were cultured on unpatterned substrata adhered and flattened extensively (approximately 10,000 microm(2)) while cells grown on 20 microm micropatterend wide adhesive strips were highly elongated with much smaller area coverage of approximately 2000 microm(2). Gene expression analysis revealed up-regulation of several hallmark markers associated to neurogenesis and myogenesis for cells that were highly elongated while osteogenic markers were specifically down-regulated or remained at its nominal level. Even though there is clearly upregulated levels of both neuronal and myogenic lineages but at the functionally relevant level of protein expression, the myogenic lineage is dominant within the time scale studied as determined by the exclusive expression of cardiac myosin heavy chain for the micropatterned cells. Enforced cell shape distortion resulting in large scale rearrangement of cytoskeletal network and altered nucleus shape has been proposed as a physical impetus by which mechanical deformation is translated into biochemical response. These results demonstrated for the first time that cellular shape modulation in the absence of any induction factors may be a viable strategy to coax lineage-specific differentiation of stem cells.

ERK5 MAP kinase regulates neurogenin1 during cortical neurogenesis

The commitment of multi-potent cortical progenitors to a neuronal fate depends on the transient induction of the basic-helix-loop-helix (bHLH) family of transcription factors including Neurogenin 1 (Neurog1). Previous studies have focused on mechanisms that control the expression of these proteins while little is known about whether their pro-neural activities can be regulated by kinase signaling pathways. Using primary cultures and ex vivo slice cultures, here we report that both the transcriptional and pro-neural activities of Neurog1 are regulated by extracellular signal-regulated kinase (ERK) 5 signaling in cortical progenitors. Activation of ERK5 potentiated, while blocking ERK5 inhibited Neurog1-induced neurogenesis. Furthermore, endogenous ERK5 activity was required for Neurog1-initiated transcription. Interestingly, ERK5 activation was sufficient to induce Neurog1 phosphorylation and ERK5 directly phosphorylated Neurog1 in vitro. We identified S179/S208 as putative ERK5 phosphorylation sites in Neurog1. Mutations of S179/S208 to alanines inhibited the transcriptional and pro-neural activities of Neurog1. Our data identify ERK5 phosphorylation of Neurog1 as a novel mechanism regulating neuronal fate commitment of cortical progenitors.

Glutamatergic neuronal differentiation of mouse embryonic stem cells after transient expression of neurogenin 1 and treatment with BDNF and GDNF: in vitro and in vivo studies

Differentiation of the pluripotent neuroepithelium into neurons and glia is accomplished by the interaction of growth factors and cell-type restricted transcription factors. One approach to obtaining a particular neuronal phenotype is by recapitulating the expression of these factors in embryonic stem (ES) cells. Toward the eventual goal of auditory nerve replacement, the aim of the current investigation was to generate auditory nerve-like glutamatergic neurons from ES cells. Transient expression of Neurog1 promoted widespread neuronal differentiation in vitro; when supplemented with brain-derived neurotrophic factor (BDNF) and glial cell line-derived neurotrophic factor (GDNF), 75% of ES cell-derived neurons attained a glutamatergic phenotype after 5 d in vitro. Mouse ES cells were also placed into deafened guinea pig cochleae and Neurog1 expression was induced for 48 h followed by 26 d of BDNF/GDNF infusion. In vivo differentiation resulted in 50-75% of ES cells bearing markers of early neurons, and a majority of these cells had a glutamatergic phenotype. This is the first study to report a high percentage of ES cell differentiation into a glutamatergic phenotype and sets the stage for cell replacement of auditory nerve.

Cdc42-mTOR signaling pathway controls Hes5 and Pax6 expression in retinoic acid-dependent neural differentiation

The conditional knockout of the small GTPase Cdc42 from neuroepithelial (NE) and radial glial (RG) cells in the mouse telencephalon has been shown to have a significant impact on brain development by causing these neural progenitor cells to detach from the apical/ventricular surface and to lose their cell identity. This has been attributed to the requirement for Cdc42 in establishing proper apical/basal cell polarity and cell-cell adhesions. In the present study, we provide new insights into the role played by Cdc42 in the maintenance of neural progenitor cells, using the mouse embryonal carcinoma P19 cell line as a model system. We show that the ability of P19 cells to undergo the transition from an Oct3/4-positive, undifferentiated status to microtubule-associated protein 2-positive neurons and glial fibrillary acidic protein-positive astrocytes, upon treatment with retinoic acid (RA), requires RA-induced activation of Cdc42 during the neural cell lineage specification phase. Experiments using chemical inhibitors and RNA interference suggest that the actions of Cdc42 are mediated through signaling pathways that start with fibroblast growth factors and Delta/Notch proteins and lead to Cdc42-dependent mTOR activation, culminating in the up-regulation of Hes5 and Pax6, two transcription factors that are essential for the maintenance of NE and RG cells. The constitutively active Cdc42(F28L) mutant was sufficient to up-regulate Hes5 and Pax6 in P19 cells, even in the absence of RA treatment, ultimately promoting their transition to neural progenitor cells. The ectopic Cdc42 expression also significantly augmented the RA-dependent up-regulation of these transcription factors, resulting in P19 cells maintaining their neural progenitor status but being unable to undergo terminal differentiation. These findings shed new light on how Cdc42 influences neural progenitor cell fate by regulating gene expression.

Basic helix-loop-helix transcription factor NEUROG1 and schizophrenia: effects on illness susceptibility, MRI brain morphometry and cognitive abilities

Transcription factors, including the basic helix-loop-helix (bHLH) family, regulate numerous genes and play vital roles in controlling gene expression. Consequently, transcription factor mutations can lead to phenotypic pleiotropy, and may be a candidate mechanism underlying the complex genetics and heterogeneous phenotype of schizophrenia. Neurogenin1 (NEUROG1; a.k.a. Ngn1 or Neurod3), a bHLH transcription factor encoded on a known schizophrenia linkage region in 5q31.1, induces glutamatergic and suppresses GABAergic neuronal differentiation during embryonic neurodevelopment. The goal of this study is to investigate NEUROG1 effects on schizophrenia risk and on phenotypic features of schizophrenia. We tested 392 patients with schizophrenia or schizoaffective disorder and 226 healthy normal volunteers for association with NEUROG1. Major alleles on two NEUROG1-associated SNPs (rs2344484-C-allele and rs8192558-G-allele) were significantly more prevalent among patients (p<or=.0018). Approximately 80% of the sample also underwent high-resolution, multi-spectral magnetic resonance brain imaging and standardized neuropsychological assessment. There were significant rs2344484 genotype main effects on total cerebral gray matter (GM) and temporal GM volumes (p<or=.05). C-allele-carrier patients and healthy volunteers had smaller total cerebral GM and temporal GM volumes than their respective T-homozygous counterparts. rs2344484-C-allele was further associated with generalized cognitive deficits among schizophrenia patients but not in healthy volunteers. Our findings replicate previous association between NEUROG1 and schizophrenia. More importantly, this is the first study to examine brain morphological and neurocognitive correlates of NEUROG1. rs2344484-C-allele may affect NEUROG1's role in transcription regulation such that brain morphology and cognitive abilities are altered resulting in increased susceptibility to develop schizophrenia.

Effect of NeuroD2 expression on neuronal differentiation in mouse embryonic stem cells

A basic helix-loop-helix transcriptional factor, NeuroD2, plays important roles in neuronal differentiation and survival. We introduced the tetracycline-dependent NeuroD2 expression system to embryonic stem (ES) cells and studied the role of NeuroD2 in the neuronal differentiation. The addition of doxycycline induced the expression of NeuroD2 after 24h and the differentiation to neurons after 3 days in ES cells, which are transfected with vectors composed of reverse tetracycline-controlled transactivator with cytomegarovirus promoter and NeuroD2 with tetracycline response element. Treatment with doxycycline for 3 days induced neuronal differentiation, but not within 1 day; furthermore NeuroD2 was detected in the nucleus 3 days after treatment, but also not within 1 day. The results suggest that the expression of NeuroD2 requires an appropriate period of about 3 days to elicit neuronal differentiation in ES cells.

Characterization of a nervous system-specific promoter for growth-associated protein 43 gene in Medaka (Oryzias latipes)

Genes expressed by neurons are controlled by specific, interacting cis-regulatory elements and trans-acting factors within their promoters. In the present study, we asked whether the transcriptional machinery regulating neuron-specific gene expression was conserved in evolution. We identified a GAP-43 homolog in Medaka (Oryzias latipes), and analyzed its expression during various stages of development. Compared with the amino acid sequences of GAP-43 homologs in other vertebrates, the amino-terminus of GAP-43 was highly conserved evolutionarily, but the carboxy-terminus exhibited significant variability. Expression of GAP-43 predominantly occurred in cells of the central and peripheral nervous systems as determined by in situ hybridization and by RT-PCR. Expression of GAP-43 increased throughout development and significant levels continued to be expressed into adulthood. We also showed that a proximal approximately 2.0 kbp fragment in the 5'-flanking region had promoter activity as determined by in vivo reporter assays. Furthermore, based upon computational analysis of transcription factor binding sites and an in vivo reporter analysis using sequentially deleted promoters, we demonstrated that cis-regulatory elements for neuronal expression were widely distributed in this region. In mammals, a TATA-box, E-box and neuronal repressive elements have been thought to contribute to neuronal expression. However, these features were not found in the orthologous region of the Medaka GAP-43 promoter. Our results suggest that the arrangement of cis-regulatory elements of the GAP-43 ortholog in Medaka is different from that in mammals, yet maintains neuron-specific regulation.

E protein dosage influences brain development more than family member identity

Loss-of-function studies have revealed the role of many basic helix-loop-helix (bHLH) transcription factors at specific points during development; however, the role of E proteins in the development of the nervous system has not been experimentally addressed. E proteins have been speculated to interact selectively with class II bHLH factors to form different neurogenic complexes. In this study, using coimmunoprecipitation in a culture model of neurogenesis (P19 cells), we show that E proteins E12, HEB, and E2-2 interact with neuroD2. Using electrophoretic mobility shift assay and P19 cell culture, we show that these heterodimers bind a neuroD2 preferred E box and induce neurogenesis equally well. We examine the mRNA levels of the three E proteins at 10 time points during brain development and show that E protein gene expression is regulated such that at certain times during development selective interaction between neuroD2 and a single E protein (HEB) is a possibility. This led us to study the brains of HEB and E2A knockout mice, which manifest no gross neuroanatomical, cellular, or behavioral deficits. These findings, together with homology in the primary peptide sequence of E proteins, suggest functional compensation among E proteins during development of the nervous system.

Cux2 (Cutl2) integrates neural progenitor development with cell-cycle progression during spinal cord neurogenesis

Neurogenesis requires the coordination of neural progenitor proliferation and differentiation with cell-cycle regulation. However, the mechanisms coordinating these distinct cellular activities are poorly understood. Here we demonstrate for the first time that a Cut-like homeodomain transcription factor family member, Cux2 (Cutl2), regulates cell-cycle progression and development of neural progenitors. Cux2 loss-of-function mouse mutants exhibit smaller spinal cords with deficits in neural progenitor development as well as in neuroblast and interneuron differentiation. These defects correlate with reduced cell-cycle progression of neural progenitors coupled with diminished Neurod and p27(Kip1) activity. Conversely, in Cux2 gain-of-function transgenic mice, the spinal cord is enlarged in association with enhanced neuroblast formation and neuronal differentiation, particularly with respect to interneurons. Furthermore, Cux2 overexpression induces high levels of Neurod and p27(Kip1). Mechanistically, we discovered through chromatin immunoprecipitation assays that Cux2 binds both the Neurod and p27(Kip1) promoters in vivo, indicating that these interactions are direct. Our results therefore show that Cux2 functions at multiple levels during spinal cord neurogenesis. Cux2 initially influences cell-cycle progression in neural progenitors but subsequently makes additional inputs through Neurod and p27(Kip1) to regulate neuroblast formation, cell-cycle exit and cell-fate determination. Thus our work defines novel roles for Cux2 as a transcription factor that integrates cell-cycle progression with neural progenitor development during spinal cord neurogenesis.

Expression of PKC substrate proteins, GAP-43 and neurogranin, is downregulated by cAMP signaling and alterations in synaptic activity

Growth-associated protein 43 (GAP-43) and neurogranin are protein kinase C substrate proteins that are thought to play an important role in synaptic plasticity, but little is currently known about the mechanisms that may regulate their function at the synapse. In this study, we show that long-term elevation of intracellular cAMP levels in rat primary cortical cultures results in a persistent downregulation of GAP-43 and neurogranin, most likely at the transcriptional level. This effect may be at least partially mediated by protein kinase A, but is independent of protein kinase C activation. Moreover, it is mimicked and occluded by manipulations that alter the levels of spontaneous synaptic activity in primary cultures, such as bicuculline and tetrodotoxin. These data suggest that levels of GAP-43 and neurogranin are regulated by factors known to modulate synaptic strength, thus providing a potential mechanism by which protein kinase C signaling pathways and their substrates might contribute to synaptic function and/or plasticity.

Neuroepithelial cells supply an initial transient wave of MSC differentiation

Mesenchymal stem cells (MSCs) are defined as cells that undergo sustained in vitro growth and are able to give rise to multiple mesenchymal lineages. Although MSCs are already used in regenerative medicine little is known about their in vivo behavior and developmental derivation. Here, we show that the earliest wave of MSC in the embryonic trunk is generated from Sox1+ neuroepithelium but not from mesoderm. Using lineage marking by direct gfp knock-in and Cre-recombinase mediated lineage tracing, we provide evidence that Sox1+ neuroepithelium gives rise to MSCs in part through a neural crest intermediate stage. This pathway can be distinguished from the pathway through which Sox1+ cells give rise to oligodendrocytes by expression of PDGFRbeta and A2B5. MSC recruitment from this pathway, however, is transient and is replaced by MSCs from unknown sources. We conclude that MSC can be defined as a definite in vivo entity recruited from multiple developmental origins.

Methylation profiles of multiple CpG island loci in extrahepatic cholangiocarcinoma versus those of intrahepatic cholangiocarcinomas

CONTEXT

CpG island hypermethylation is attracting attention because of its importance as a tumor marker and its potential mechanism for the development of human cancers. Extrahepatic cholangiocarcinoma has been poorly investigated with respect to CpG island hypermethylation, and the number of genes known to be methylated in extrahepatic cholangiocarcinomas is fewer than 20.

OBJECTIVE

To generate methylation profiles of 24 CpG island loci in extrahepatic cholangiocarcinomas, to correlate methylation findings with clinicopathologic findings, and to compare these findings with those of intrahepatic cholangiocarcinomas.

DESIGN

Sixty-three extrahepatic cholangiocarcinomas and 48 intrahepatic cholangiocarcinomas were investigated for hypermethylation in 24 CpG island loci by using methylation-specific polymerase chain reaction.

RESULTS

A total of 61 (96.8%) of 63 extrahepatic cholangiocarcinomas showed hypermethylation in at least one of the examined loci, and a high methylation frequency was seen in HOXA1 (95.2%), HPP1 (69.8%), and NEUROG1 (61.9%). The number of methylated CpG island loci was greater in extrahepatic cholangiocarcinomas with nodal metastasis than in those without nodal metastasis (P = .047), and hypermethylation of TIG1 was closely associated with nodal metastasis of extrahepatic cholangiocarcinomas (P = .007). CDH1 and NEUROG1 were more frequently methylated in extrahepatic cholangiocarcinoma than in intrahepatic cholangiocarcinoma, whereas CHFR, GSTP1, IGF2, MGMT, MINT31, p14, and RBP1 were more frequently methylated in intrahepatic cholangiocarcinoma: the differences was statistically significant (P < .05).

CONCLUSIONS

A close relationship exists between CpG island hypermethylation and nodal metastasis of extrahepatic cholangiocarcinomas. Methylation profiles of extrahepatic cholangiocarcinomas are somewhat similar to but distinct from those of intrahepatic cholangiocarcinomas.

In vivo regulation of an Aplysia glutamate transporter, ApGT1, during long-term memory formation

Regulation of glutamate transporters often accompanies glutamatergic synaptic plasticity. We investigated the mechanisms responsible for the increase in glutamate uptake associated with increased glutamate release at the Aplysia sensorimotor synapse during long-term sensitization (LTS) and long-term facilitation. An increase in the V(max) of transport, produced by LTS training, suggested that the increased glutamate uptake was due to an increase in the number of transporters in the membrane. We cloned a high-affinity, Na(+)-dependent glutamate transporter, ApGT1, from Aplysia central nervous system that is highly enriched in pleural sensory neurons, and in pleural-pedal synaptosome and cell/glial fractions. ApGT1, expressed in Xenopus oocytes, demonstrated a similar pharmacological profile to glutamate uptake in Aplysia synaptosome and cell/glial fractions (strong inhibition by threo-beta-benzyloxyaspartate and weak inhibition by dihydrokainate) suggesting that ApGT1 may be the primary glutamate transporter in pleural-pedal ganglia. Levels of ApGT1 and glutamate uptake were increased in synaptosomes 24 h after induction of LTS by electrical stimulation or serotonin. Regulation of ApGT1 during LTS appears to occur post-transcriptionally and results in an increased number of transporters in synaptic membranes. These results suggest that an increase in levels of ApGT1 is responsible, at least in part, for the long-term increase in glutamate uptake associated with long-term memory.

Comparative genomics modeling of the NRSF/REST repressor network: from single conserved sites to genome-wide repertoire

We constructed and applied an open source informatic framework called Cistematic in an effort to predict the target gene repertoire for transcription factors with large binding sites. Cistematic uses two different evolutionary conservation-filtering algorithms in conjunction with several analysis modules. Beginning with a single conserved and biologically tested site for the neuronal repressor NRSF/REST, Cistematic generated a refined PSFM (position specific frequency matrix) based on conserved site occurrences in mouse, human, and dog genomes. Predictions from this model were validated by chromatin immunoprecipitation (ChIP) followed by quantitative PCR. The combination of transfection assays and ChIP enrichment data provided an objective basis for setting a threshold for membership and rank-ordering a final gene cohort model consisting of 842 high-confidence sites in the human genome associated with 733 genes. Statistically significant enrichment of NRSE-associated genes was found for neuron-specific Gene Ontology (GO) terms and neuronal mRNA expression profiles. A more extensive evolutionary survey showed that NRSE sites matching the PSFM model exist in roughly similar numbers in all fully sequenced vertebrate genomes but are notably absent from invertebrate and protochordate genomes, as is NRSF itself. Some NRSF/REST sites reside in repeats, which suggests a mechanism for both ancient and modern dispersal of NRSEs through vertebrate genomes. Multiple predicted sites are located near neuronal microRNA and splicing-factor genes, and these tested positive for NRSF/REST occupancy in vivo. The resulting network model integrates post-transcriptional and translational controllers, including candidate feedback loops on NRSF and its corepressor, CoREST.

Congenital hypothyroidism (cretinism) in neuroD2-deficient mice

Mice lacking neuroD2, a basic helix-loop-helix transcription factor involved in brain development, show growth retardation and other abnormalities consistent with hypothalamic-pituitary-thyroid (HPT) axis dysfunction. neuroD2 is expressed in the paraventricular hypothalamic nuclei, the anterior lobe of pituitary, and the thyroid gland. In neuroD2-deficient mice, thyrotropin-releasing hormone, thyroid-stimulating hormone, and thyroid hormone are decreased in these three regions, respectively. neuroD2-null mice typically die 2 to 3 weeks after birth, but those treated with replacement doses of thyroxine survived more than 8 weeks. These data indicate that neuroD2 is expressed throughout the HPT axis and that all levels of the axis are functionally affected by its absence in mice.

Regulation of Thalamocortical Patterning and Synaptic Maturation by NeuroD2

During cortical development, both activity-dependent and genetically determined mechanisms are required to establish proper neuronal connectivity. While activity-dependent transcription may link the two processes, specific transcription factors that mediate such a process have not been identified. We identified the basic helix-loop-helix (bHLH) transcription factor Neurogenic Differentiation 2 (NeuroD2) in a screen for calcium-regulated transcription factors and report that it is required for the proper development of thalamocortical connections. In neuroD2 null mice, thalamocortical axon terminals fail to segregate in the somatosensory cortex, and the postsynaptic barrel organization is disrupted. Additionally, synaptic transmission is defective at thalamocortical synapses in neuroD2 null mice. Total excitatory synaptic currents are reduced in layer IV in the knockouts, and the relative contribution of AMPA and NMDA receptor-mediated currents to evoked responses is decreased. These observations indicate that NeuroD2 plays a critical role in regulating synaptic maturation and the patterning of thalamocortical connections.

Involvement of the mouse Prp19 gene in neuronal/astroglial cell fate decisions

The molecular mechanisms involved in neuronal/astroglial cell fate decisions during the development of the mammalian central nervous system are poorly understood. Here, we report that PRP19beta, a splice variant of mouse PRP19alpha corresponding to the yeast PRP19 protein, can function as a neuron-astroglial switch during the retinoic acid-primed neural differentiation of P19 cells. The beta-variant possesses an additional 19 amino acid residues in-frame in the N-terminal region of the alpha-variant. The forced expression of the alpha-variant RNA caused the down-regulation of oct-3/4 and nanog mRNA expression during the 12-48 h of the late-early stages of neural differentiation and was sufficient to convert P19 cells into neurons (but not glial cells) when the cells were cultured in aggregated form without retinoic acid. In contrast, the forced expression of the beta-variant RNA suppressed neuronal differentiation and conversely stimulated astroglial cell differentiation in retinoic acid-primed P19 cells. Based on yeast two-hybrid screening, cyclophilin A was identified as a specific binding partner of the beta-variant. Luciferase reporter assay mediated by the oct-3/4 promoter revealed that cyclophilin A could act as a transcriptional activator and that its activity was suppressed by the beta-variant, suggesting that cyclophilin A takes part in the induction of oct-3/4 gene expression, which might lead to neuroectodermal otx2 expression within 12 h of the immediate-early stages of retinoic acid-primed neural differentiation. These results show that the alpha-variant gene plays a pivotal role in neural differentiation and that the beta-variant participates in neuronal/astroglial cell fate decisions.

Regulation of dendritic development by calcium signaling

Neuronal activity can have profound effects on dendrite morphology in the developing brain. The effects of neuronal activity on dendritic morphology are mediated by calcium signaling. While many effects of calcium on dendrite structure occur locally at the site of calcium entry into the cytoplasmic milieu, elevation of cytoplasmic calcium is also translated into changes in gene transcription. Decoding the calcium signal into specific changes in gene transcription involve coordinating the action of a number of kinases, phosphatases, transcription factors and transcriptional coactivators. This review focuses on the contribution of calcium-dependent transcription on the control of dendritic morphology.

Suppression of Stat3 promotes neurogenesis in cultured neural stem cells

To investigate the effects of signal transducer and activator of transcription 3 (Stat3) on neural stem cell fate, stem cells were inoculated with an adenovirus vector expressing dominant negative form of Stat3 (Stat3F). One day later, a promoter assay revealed significant reduction of the transcriptional level in the transfected cells. Three days later, Western blot analysis and immunocytochemical analysis revealed that the protein level of microtubule-associated protein (MAP)2 and the number of MAP2-positive cells were increased significantly in the transfected cells whereas the protein level of glial fibrillary acidic protein (GFAP) and the number of GFAP-positive cells were decreased significantly. In addition, mRNA levels of Notch family members (Notch1, 2, and 3) and of inhibitory basic helix-loop-helix (bHLH) factors (Hes5, Id2, and Id3) were significantly downregulated at 3 days after viral inoculation with Stat3F; however, mRNA levels of bHLH determination factors (Math1 and Neurogenin3) and bHLH differentiation factors (NeuroD1 and NeuroD2) were significantly upregulated. These data indicated that suppression of Stat3 directly induced neurogenesis and inhibited astrogliogenesis in neural stem cells.

Microarray analysis of the genes induced by tetracycline-regulated expression of NDRF/NeuroD2 in P19 cells

NeuroD-related factor (NDRF)/NeuroD2 is a basic helix-loop-helix (bHLH) protein that plays important roles in neuronal development. To elucidate the NDRF transcription network, we used mouse cDNA microarray analysis combined with a tetracycline-regulatable expression system in P19 embryonal carcinoma cells. Five genes were identified to be up-regulated in the presence of NDRF protein. RNA hybridization analysis confirmed that brain-lipid-binding protein (BLBP) and inhibitor of differentiation 1 (Id1) genes were among the five genes that were rapidly and significantly up-regulated after induction of NDRF. When a dominant negative form of NDRF protein was expressed during retinoic acid-induced neuronal differentiation of P19 cells, the BLBP gene, but not the Id1 gene, was potently repressed. Immunohistochemical analysis revealed that both NDRF and Id1 immunoreactivities were observed in some granule cells of the cerebellum in the postnatal period. These results suggest that NDRF or its related bHLH proteins may act upstream of these genes in a subset of developing neurons.

A CaMKII-NeuroD signaling pathway specifies dendritic morphogenesis

The elaboration of dendrites is fundamental to the establishment of neuronal polarity and connectivity, but the mechanisms that underlie dendritic morphogenesis are poorly understood. We found that the genetic knockdown of the transcription factor NeuroD in primary granule neurons including in organotypic cerebellar slices profoundly impaired the generation and maintenance of dendrites while sparing the development of axons. We also found that NeuroD mediated neuronal activity-dependent dendritogenesis. The activity-induced protein kinase CaMKII catalyzed the phosphorylation of NeuroD at distinct sites, including endogenous NeuroD at Ser336 in primary neurons, and thereby stimulated dendritic growth. These findings uncover an essential function for NeuroD in granule neuron dendritic morphogenesis. Our study also defines the CaMKII-NeuroD signaling pathway as a novel mechanism underlying activity-regulated dendritic growth that may play important roles in the developing and mature brain.