Brain lipid-binding protein is a direct target of Notch signaling in radial glial cells

In Vivo Monitoring of Fabp7 Expression in Transgenic Zebrafish

In zebrafish, like in mammals, radial glial cells (RGCs) can act as neural progenitors during development and regeneration in adults. However, the heterogeneity of glia subpopulations entails the need for different specific markers of zebrafish glia. Currently, fluorescent protein expression mediated by a regulatory element from the glial fibrillary acidic protein (gfap) gene is used as a prominent glia reporter. We now expand this tool by demonstrating that a regulatory element from the mouse Fatty acid binding protein 7 (Fabp7) gene drives reliable expression in fabp7-expressing zebrafish glial cells. By using three different Fabp7 regulatory element-mediated fluorescent protein reporter strains, we reveal in double transgenic zebrafish that progenitor cells expressing fluorescent proteins driven by the Fabp7 regulatory element give rise to radial glia, oligodendrocyte progenitors, and some neuronal precursors. Furthermore, Bergmann glia represent the almost only glial population of the zebrafish cerebellum (besides a few oligodendrocytes), and the radial glia also remain in the mature cerebellum. Fabp7 regulatory element-mediated reporter protein expression in Bergmann glia progenitors suggests their origin from the ventral cerebellar proliferation zone, the ventricular zone, but not from the dorsally positioned upper rhombic lip. These new Fabp7 reporters will be valuable for functional studies during development and regeneration.

The emerging role of fatty acid binding protein 7 (FABP7) in cancers

Fatty acid binding protein 7 (FABP7) is an intracellular protein involved in the uptake, transportation, metabolism, and storage of fatty acids (FAs). FABP7 is upregulated up to 20-fold in multiple cancers, usually correlated with poor prognosis. FABP7 silencing or pharmacological inhibition suggest FABP7 promotes cell growth, migration, invasion, colony and spheroid formation/increased size, lipid uptake, and lipid droplet formation. Xenograft studies show that suppression of FABP7 inhibits tumour formation and tumour growth, and improves host survival. The molecular mechanisms involve promotion of FA uptake, lipid droplets, signalling [focal adhesion kinase (FAK), proto-oncogene tyrosine-protein kinase Src (Src), mitogen-activated protein kinase kinase/p-extracellular signal-regulated kinase (MEK/ERK), and Wnt/β-catenin], hypoxia-inducible factor 1-alpha (Hif1α), vascular endothelial growth factor A/prolyl 4-hydroxylase subunit alpha-1 (VEGFA/P4HA1), snail family zinc finger 1 (Snail1), and twist-related protein 1 (Twist1). The oncogenic capacity of FABP7 makes it a promising pharmacological target for future cancer treatments.

Cerebral organoids derived from patients with Alzheimer's disease with PSEN1/2 mutations have defective tissue patterning and altered development

During the past two decades, induced pluripotent stem cells (iPSCs) have been widely used to study human neural development and disease. Especially in the field of Alzheimer's disease (AD), remarkable effort has been put into investigating molecular mechanisms behind this disease. Then, with the advent of 3D neuronal cultures and cerebral organoids (COs), several studies have demonstrated that this model can adequately mimic familial and sporadic AD. Therefore, we created an AD-CO model using iPSCs derived from patients with familial AD forms and explored early events and the progression of AD pathogenesis. Our study demonstrated that COs derived from three AD-iPSC lines with PSEN1(A246E) or PSEN2(N141I) mutations developed the AD-specific markers in vitro, yet they also uncover tissue patterning defects and altered development. These findings are complemented by single-cell sequencing data confirming this observation and uncovering that neurons in AD-COs likely differentiate prematurely.

N4BP1 mediates RAM domain-dependent notch signaling turnover during neocortical development

Notch signaling pathway activity, particularly fluctuations in the biologically active effector fragment NICD, is required for rapid and efficient dynamic regulation of proper fate decisions in stem cells. In this study, we identified NEDD4-binding protein 1 (N4BP1), which is highly expressed in the developing mouse cerebral cortex, as a negative modulator of Notch signaling dynamics in neural progenitor cells. Intriguingly, N4BP1 regulated NICD stability specifically after Notch1 S3 cleavage through ubiquitin-mediated degradation that depended on its RAM domain, not its PEST domain, as had been extensively and previously described. The CoCUN domain in N4BP1, particularly the "Phe-Pro" motif (862/863 amino acid), was indispensable for mediating NICD degradation. The Ring family E3 ligase Trim21 was, in contrast to other NEDD4 family members, required for N4BP1-regulated NICD degradation. Overexpression of N4BP1 in cortical neural progenitors promoted neural stem cell differentiation, whereas neural progenitor cells lacking N4BP1 were sensitized to Notch signaling, resulting in the maintenance of stem-like properties in neural progenitor cells and lower production of cortical neurons.

Description of trunk neural crest migration and peripheral nervous system formation in the Egyptian cobra Naja haje haje

The neural crest is a stem cell population that forms in the neurectoderm of all vertebrates and gives rise to a diverse set of cells such as sensory neurons, Schwann cells and melanocytes. Neural crest development in snakes is still poorly understood. From the point of view of evolutionary and comparative anatomy is an interesting topic given the unique anatomy of snakes. The aim of the study was to characterize how trunk neural crest cells (TNCC) migrate in the developing elapid snake Naja haje haje and consequently, look at the beginnings of development of neural crest derived sensory ganglia (DRG) and spinal nerves. We found that trunk neural crest and DRG development in Naja haje haje is like what has been described in other vertebrates and the colubrid snake strengthening our knowledge on the conserved mechanisms of neural crest development across species. Here we use the marker HNK1 to follow the migratory behavior of TNCC in the elapid snake Naja haje haje through stages 1-6 (1-9 days postoviposition). We observed that the TNCC of both snake species migrate through the rostral portion of the somite, a pattern also conserved in birds and mammals. The development of cobra peripheral nervous system, using neuronal and glial markers, showed the presence of spectrin in Schwann cell precursors and of axonal plexus along the length of the cobra embryos. In conclusion, cobra embryos show strong conserved patterns in TNCC and PNS development among vertebrates.

Potential effects of brain lipid binding protein in the pathogenesis of amyotrophic lateral sclerosis

Current studies suggest that the abnormal alteration of brain lipid binding protein (BLBP) might participate in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, the detailed understanding of ALS pathogenesis been yet to be elucidated. Therefore, this research intended to explore the potential effects of BLBP in ALS. The observation and analysis of BLBP-altered features in various anatomical areas and different spinal segments was conducted at the pre-onset, onset, and progression stages of Tg(SOD1*G93A)1Gur (TG) mice and the same periods of age-matched SOD1 wild-type (WT) mice by fluorescence immunohistochemistry and western blotting. BLBP-positive cells were comprehensively distributed in various spinal anatomical areas, especially in both the anterior and posterior horn, around the central canal and in anterior, lateral, and posterior funiculi. Overall, BLBP expression tended to increase from the pre-onset to the onset to the progression stages of the same periods of age-matched WT mice. Furthermore, in TG mice, BLBP expression in the entire spinal cord significantly increased from onset to the progression stage. BLBP was expressed in neurons, astrocytes, and radial glial cells, and at the early and late stages of neural precursor cells (NPCs) and was predominantly distributed outside the cell nucleus. The increase of BLBP-positive cells was closely related to neural cell reduction in TG mice. The distribution and increased expression of BLBP among the cervical, thoracic, and lumbar segments of the spinal cord might participate in the development of ALS and exert potential effects in the pathogenesis of ALS by regulating NPCs.

FABP7: a glial integrator of sleep, circadian rhythms, plasticity, and metabolic function

Sleep and circadian rhythms are observed broadly throughout animal phyla and influence neural plasticity and cognitive function. However, the few phylogenetically conserved cellular and molecular pathways that are implicated in these processes are largely focused on neuronal cells. Research on these topics has traditionally segregated sleep homeostatic behavior from circadian rest-activity rhythms. Here we posit an alternative perspective, whereby mechanisms underlying the integration of sleep and circadian rhythms that affect behavioral state, plasticity, and cognition reside within glial cells. The brain-type fatty acid binding protein, FABP7, is part of a larger family of lipid chaperone proteins that regulate the subcellular trafficking of fatty acids for a wide range of cellular functions, including gene expression, growth, survival, inflammation, and metabolism. FABP7 is enriched in glial cells of the central nervous system and has been shown to be a clock-controlled gene implicated in sleep/wake regulation and cognitive processing. FABP7 is known to affect gene transcription, cellular outgrowth, and its subcellular localization in the fine perisynaptic astrocytic processes (PAPs) varies based on time-of-day. Future studies determining the effects of FABP7 on behavioral state- and circadian-dependent plasticity and cognitive processes, in addition to functional consequences on cellular and molecular mechanisms related to neural-glial interactions, lipid storage, and blood brain barrier integrity will be important for our knowledge of basic sleep function. Given the comorbidity of sleep disturbance with neurological disorders, these studies will also be important for our understanding of the etiology and pathophysiology of how these diseases affect or are affected by sleep.

Minimal gene set discovery in single-cell mRNA-seq datasets with ActiveSVM

Sequencing costs currently prohibit the application of single-cell mRNA-seq to many biological and clinical analyses. Targeted single-cell mRNA-sequencing reduces sequencing costs by profiling reduced gene sets that capture biological information with a minimal number of genes. Here we introduce an active learning method that identifies minimal but highly informative gene sets that enable the identification of cell types, physiological states and genetic perturbations in single-cell data using a small number of genes. Our active feature selection procedure generates minimal gene sets from single-cell data by employing an active support vector machine (ActiveSVM) classifier. We demonstrate that ActiveSVM feature selection identifies gene sets that enable ~90% cell-type classification accuracy across, for example, cell atlas and disease-characterization datasets. The discovery of small but highly informative gene sets should enable reductions in the number of measurements necessary for application of single-cell mRNA-seq to clinical tests, therapeutic discovery and genetic screens.

Developmental Neuropathology and Neurodegeneration of Down Syndrome: Current Knowledge in Humans

Individuals with Down syndrome (DS) suffer from developmental delay, intellectual disability, and an early-onset of neurodegeneration, Alzheimer’s-like disease, or precocious dementia due to an extra chromosome 21. Studying the changes in anatomical, cellular, and molecular levels involved may help to understand the pathogenesis and develop target treatments, not just medical, but also surgical, cell and gene therapy, etc., for individuals with DS. Here we aim to identify key neurodevelopmental manifestations, locate knowledge gaps, and try to build molecular networks to better understand the mechanisms and clinical importance. We summarize current information about the neuropathology and neurodegeneration of the brain from conception to adulthood of foetuses and individuals with DS at anatomical, cellular, and molecular levels in humans. Understanding the alterations and characteristics of developing Down syndrome will help target treatment to improve the clinical outcomes. Early targeted intervention/therapy for the manifestations associated with DS in either the prenatal or postnatal period may be useful to rescue the neuropathology and neurodegeneration in DS.

Fatty acid-binding proteins and fatty acid synthase influence glial reactivity and promote the formation of Müller glia-derived progenitor cells in the chick retina

A recent comparative transcriptomic study of Müller glia (MG) in vertebrate retinas revealed that fatty acid binding proteins (FABPs) are among the most highly expressed genes in chick ( Hoang et al., 2020). Here, we investigate how FABPs and fatty acid synthase (FASN) influence glial cells in the chick retina. During development, FABP7 is highly expressed by retinal progenitor cells and maturing MG, whereas FABP5 is upregulated in maturing MG. PMP2 (FABP8) is expressed by oligodendrocytes and FABP5 is expressed by non-astrocytic inner retinal glial cells, and both of these FABPs are upregulated by activated MG. In addition to suppressing the formation of Müller glia-derived progenitor cells (MGPCs), we find that FABP-inhibition suppresses the proliferation of microglia. FABP-inhibition induces distinct changes in single cell transcriptomic profiles, indicating transitions of MG from resting to reactive states and suppressed MGPC formation, with upregulation of gene modules for gliogenesis and decreases in neurogenesis. FASN-inhibition increases the proliferation of microglia and suppresses the formation of MGPCs. We conclude that fatty acid metabolism and cell signaling involving fatty acids are important in regulating the reactivity and dedifferentiation of MG, and the proliferation of microglia and MGPCs.

Cell cycle arrest determines adult neural stem cell ontogeny by an embryonic Notch-nonoscillatory Hey1 module

Quiescent neural stem cells (NSCs) in the adult mouse brain are the source of neurogenesis that regulates innate and adaptive behaviors. Adult NSCs in the subventricular zone are derived from a subpopulation of embryonic neural stem-progenitor cells (NPCs) that is characterized by a slower cell cycle relative to the more abundant rapid cycling NPCs that build the brain. Yet, how slow cell cycle can cause the establishment of adult NSCs remains largely unknown. Here, we demonstrate that Notch and an effector Hey1 form a module that is upregulated by cell cycle arrest in slowly dividing NPCs. In contrast to the oscillatory expression of the Notch effectors Hes1 and Hes5 in fast cycling progenitors, Hey1 displays a non-oscillatory stationary expression pattern and contributes to the long-term maintenance of NSCs. These findings reveal a novel division of labor in Notch effectors where cell cycle rate biases effector selection and cell fate.

Adult neural stem cells are derived from an embryonic population of slowcycling progenitor cells, though how reduced cycling speed leads to establishment of the adult population has remained elusive. Here they show that non-oscillatory Notch-Hey signaling induced by slow-cycling contributes to long term maintenance of neural stem cells.

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.

BLBP Is Both a Marker for Poor Prognosis and a Potential Therapeutic Target in Paediatric Ependymoma

Paediatric ependymomas are aggressive, treatment-resistant tumours with a tendency towards relapse, consistent with a sub-population of therapy-resistant cancer stem cells. These cells are believed to derive from brain lipid binding protein (BLBP)-expressing radial glia, hence we proposed that BLBP may be a marker for ependymoma therapy resistance. BLBP protein expression correlated with reduced overall survival (OS) in patients from two trials (CNS9204, a chemotherapy-led infant trial-5 y OS 45% vs. 80%, p = 0.011-and CNS9904, a radiotherapy-led trial-OS 38% vs. 85%, p = 0.002). All ependymoma cell lines examined by qRT-PCR expressed BLBP, with expression elevated in stem cell-enriched neurospheres. Modulation of BLBP function in 2D and 3D assays, using either peroxisome proliferator activated receptor (PPAR) antagonists or BLBP's fatty acid substrate docosahexaneoic acid (DHA), potentiated chemotherapy response and reduced cell migration and invasion in ependymoma cell lines. BLBP is therefore an independent predictor of poor survival in paediatric ependymoma, and treatment with PPAR antagonists or DHA may represent effective novel therapies, preventing chemotherapy resistance and invasion in paediatric ependymoma patients.

Targeting Loss of Heterozygosity: A Novel Paradigm for Cancer Therapy

Loss of heterozygosity (LOH) is a common genetic event in the development of cancer. In certain tumor types, LOH can affect more than 20% of the genome, entailing loss of allelic variation in thousands of genes. This reduction of heterozygosity creates genetic differences between tumor and normal cells, providing opportunities for development of novel cancer therapies. Here, we review and summarize (1) mutations associated with LOH on chromosomes which have been shown to be promising biomarkers of cancer risk or the prediction of clinical outcomes in certain types of tumors; (2) loci undergoing LOH that can be targeted for development of novel anticancer drugs as well as (3) LOH in tumors provides up-and-coming possibilities to understand the underlying mechanisms of cancer evolution and to discover novel cancer vulnerabilities which are worth a further investigation in the near future.

Familial Alzheimer's Disease Mutations in PSEN1 Lead to Premature Human Stem Cell Neurogenesis

Mutations in presenilin 1 (PSEN1) or presenilin 2 (PSEN2), the catalytic subunit of γ-secretase, cause familial Alzheimer's disease (fAD). We hypothesized that mutations in PSEN1 reduce Notch signaling and alter neurogenesis. Expression data from developmental and adult neurogenesis show relative enrichment of Notch and γ-secretase expression in stem cells, whereas expression of APP and β-secretase is enriched in neurons. We observe premature neurogenesis in fAD iPSCs harboring PSEN1 mutations using two orthogonal systems: cortical differentiation in 2D and cerebral organoid generation in 3D. This is partly driven by reduced Notch signaling. We extend these studies to adult hippocampal neurogenesis in mutation-confirmed postmortem tissue. fAD cases show mutation-specific effects and a trend toward reduced abundance of newborn neurons, supporting a premature aging phenotype. Altogether, these results support altered neurogenesis as a result of fAD mutations and suggest that neural stem cell biology is affected in aging and disease.

Oncogenic and Tumor-Suppressive Functions of NOTCH Signaling in Glioma

Although the role of NOTCH signaling has been extensively studied in health and disease, many questions still remain unresolved. Being crucial for tissue homeostasis, NOTCH signaling is also implicated in multiple cancers by either promoting or suppressing tumor development. In this review we illustrate the context-dependent role of NOTCH signaling during tumorigenesis with a particular focus on gliomas, the most frequent and aggressive brain tumors in adults. For a long time, NOTCH has been considered an oncogene in glioma mainly by virtue of its neural stem cell-promoting activity. However, the recent identification of NOTCH-inactivating mutations in some glioma patients has challenged this notion, prompting a re-examination of the function of NOTCH in brain tumor subtypes. We discuss recent findings that might help to reconcile the controversial role of NOTCH signaling in this disease, and pose outstanding questions that still remain to be addressed.

Comparative gene expression profiling between optic nerve and spinal cord injury in Xenopus laevis reveals a core set of genes inherent in successful regeneration of vertebrate central nervous system axons

BACKGROUND

The South African claw-toed frog, Xenopus laevis, is uniquely suited for studying differences between regenerative and non-regenerative responses to CNS injury within the same organism, because some CNS neurons (e.g., retinal ganglion cells after optic nerve crush (ONC)) regenerate axons throughout life, whereas others (e.g., hindbrain neurons after spinal cord injury (SCI)) lose this capacity as tadpoles metamorphose into frogs. Tissues from these CNS regions (frog ONC eye, tadpole SCI hindbrain, frog SCI hindbrain) were used in a three-way RNA-seq study of axotomized CNS axons to identify potential core gene expression programs for successful CNS axon regeneration.

RESULTS

Despite tissue-specific changes in expression dominating the injury responses of each tissue, injury-induced changes in gene expression were nonetheless shared between the two axon-regenerative CNS regions that were not shared with the non-regenerative region. These included similar temporal patterns of gene expression and over 300 injury-responsive genes. Many of these genes and their associated cellular functions had previously been associated with injury responses of multiple tissues, both neural and non-neural, from different species, thereby demonstrating deep phylogenetically conserved commonalities between successful CNS axon regeneration and tissue regeneration in general. Further analyses implicated the KEGG adipocytokine signaling pathway, which links leptin with metabolic and gene regulatory pathways, and a novel gene regulatory network with genes regulating chromatin accessibility at its core, as important hubs in the larger network of injury response genes involved in successful CNS axon regeneration.

CONCLUSIONS

This study identifies deep, phylogenetically conserved commonalities between CNS axon regeneration and other examples of successful tissue regeneration and provides new targets for studying the molecular underpinnings of successful CNS axon regeneration, as well as a guide for distinguishing pro-regenerative injury-induced changes in gene expression from detrimental ones in mammals.

Midbrain Dopaminergic Neuron Development at the Single Cell Level: In vivo and in Stem Cells

Parkinson's disease (PD) is a progressive neurodegenerative disorder that predominantly affects dopaminergic (DA) neurons of the substantia nigra. Current treatment options for PD are symptomatic and typically involve the replacement of DA neurotransmission by DA drugs, which relieve the patients of some of their motor symptoms. However, by the time of diagnosis, patients have already lost about 70% of their substantia nigra DA neurons and these drugs offer only temporary relief. Therefore, cell replacement therapy has garnered much interest as a potential treatment option for PD. Early studies using human fetal tissue for transplantation in PD patients provided proof of principle for cell replacement therapy, but they also highlighted the ethical and practical difficulties associated with using human fetal tissue as a cell source. In recent years, advancements in stem cell research have made human pluripotent stem cells (hPSCs) an attractive source of material for cell replacement therapy. Studies on how DA neurons are specified and differentiated in the developing mouse midbrain have allowed us to recapitulate many of the positional and temporal cues needed to generate DA neurons in vitro. However, little is known about the developmental programs that govern human DA neuron development. With the advent of single-cell RNA sequencing (scRNA-seq) and bioinformatics, it has become possible to analyze precious human samples with unprecedented detail and extract valuable high-quality information from large data sets. This technology has allowed the systematic classification of cell types present in the human developing midbrain along with their gene expression patterns. By studying human development in such an unbiased manner, we can begin to elucidate human DA neuron development and determine how much it differs from our knowledge of the rodent brain. Importantly, this molecular description of the function of human cells has become and will increasingly be a reference to define, evaluate, and engineer cell types for PD cell replacement therapy and disease modeling.

The Implications for Cells of the Lipid Switches Driven by Protein-Membrane Interactions and the Development of Membrane Lipid Therapy

The cell membrane contains a variety of receptors that interact with signaling molecules. However, agonist-receptor interactions not always activate a signaling cascade. Amphitropic membrane proteins are required for signal propagation upon ligand-induced receptor activation. These proteins localize to the plasma membrane or internal compartments; however, they are only activated by ligand-receptor complexes when both come into physical contact in membranes. These interactions enable signal propagation. Thus, signals may not propagate into the cell if peripheral proteins do not co-localize with receptors even in the presence of messengers. As the translocation of an amphitropic protein greatly depends on the membrane's lipid composition, regulation of the lipid bilayer emerges as a novel therapeutic strategy. Some of the signals controlled by proteins non-permanently bound to membranes produce dramatic changes in the cell's physiology. Indeed, changes in membrane lipids induce translocation of dozens of peripheral signaling proteins from or to the plasma membrane, which controls how cells behave. We called these changes "lipid switches", as they alter the cell's status (e.g., proliferation, differentiation, death, etc.) in response to the modulation of membrane lipids. Indeed, this discovery enables therapeutic interventions that modify the bilayer's lipids, an approach known as membrane-lipid therapy (MLT) or melitherapy.

Typical halogenated flame retardants affect human neural stem cell gene expression during proliferation and differentiation via glycogen synthase kinase 3 beta and T3 signaling

2',2',4,4'-tetrabromo diphenyl ether (BDE-47), one of the most abundant congeners of commercial pentaBDE utilized as flame retardants, has been phased out of production due to its potential neural toxicity and endocrine disrupting activities, and yet still present in the environment. Several alternatives to BDE-47, including tetrabromobisphenol A (TBBPA), tetrabromobisphenol S (TBBPS), tetrachlorobisphenol A (TCBPA) and decabromodiphenyl ether (BDE-209), are presently employed without restrictions and their potential toxic effects on human neural development are still unclear. In this study, we utilized a human neural stem cell (hNSC)-based system to evaluate the potential developmental neurotoxic effects of the above-mentioned five chemicals, at environment and human exposure relevant concentrations. We found that those compounds slightly altered the expression of hNSC identity markers (SOX2, SOX3 and NES), without impairing cell viability or proliferation, in part by either modulating glycogen synthase kinase 3 beta (GSK3β) signaling (TBBPS, TCBPA and BDE-47), and slightly disturbing the NOTCH pathway (TBBPA, TBBPS and TCBPA). Moreover, the five chemicals seemed to alter hNSC differentiation by perturbing triiodothyronine (T3) cellular signaling. Thus, our findings suggest that the five compounds, especially TBBPS, TCBPA, and BDE-47, may affect hNSC self-renewal and differentiation abilities and potentially elicit neural developmental toxicity.

FABP7 is a key metabolic regulator in HER2+ breast cancer brain metastasis

Overexpression of human epidermal growth factor receptor 2 (HER2) in breast cancer patients is associated with increased incidence of breast cancer brain metastases (BCBM), but the mechanisms underlying this phenomenon remain unclear. Here, to identify brain-predominant genes critical for the establishment of BCBM, we conducted an in silico screening analysis and identified that increased levels of fatty acid-binding protein 7 (FABP7) correlate with a lower survival and higher incidence of brain metastases in breast cancer patients. We validated these findings using HER2+ BCBM cells compared with parental breast cancer cells. Importantly, through knockdown and overexpression assays, we characterized the role of FABP7 in the BCBM process in vitro and in vivo. Our results uncover a key role of FABP7 in metabolic reprogramming of HER2 + breast cancer cells, supporting a glycolytic phenotype and storage of lipid droplets that enable their adaptation and survival in the brain microenvironment. In addition, FABP7 is shown to be required for upregulation of key metastatic genes and pathways, such as integrins-Src and VEGFA, and for the growth of HER2+ breast cancer cells in the brain microenvironment in vivo. Together, our results support FABP7 as a potential target for the treatment of HER2+ BCBM.

The role of fatty acid binding protein 7 in spinal cord astrocytes in a mouse model of experimental autoimmune encephalomyelitis

Fatty acid binding protein 7 (FABP7) is expressed in astrocytes of the developing and mature central nervous system, and modulates astrocyte function by controlling intracellular fatty acid homeostasis. Astrocytes in the spinal cord have an important role in the process of myelin degeneration and regeneration. In the present study, the authors examined the role of FABP7 in astrocytes in a mouse model of experimental autoimmune encephalomyelitis (EAE), which is an established model of multiple sclerosis (MS). FABP7 was expressed in the white matter astrocytes and increased after EAE onset; particularly strong expression was observed in demyelinating regions. In FABP7-knockout (KO) mice, the onset of EAE symptoms occurred earlier than in wild type (WT) mice, and mRNA expression levels of inflammatory cytokines (IL-17 and TNF-α) were higher in FABP7-KO lumbar spinal cord than in WT lumbar spinal cord at early stage of EAE. Interestingly, however, the clinical score was significantly reduced in FABP7-KO mice compared with WT mice in the late phase of EAE. Moreover, the area exhibiting expression of fibronectin, which is an extracellular matrix protein mainly produced by astrocytes and inhibits remyelination of oligodendrocytes, was significantly decreased in FABP7-KO compared with WT mice. Collectively, FABP7 in astrocyte may have a role to protect from the induction of inflammation leading to demyelination in CNS at early phase of EAE. Moreover, FABP7 may be involved in the regulation of fibronectin production through the modification of astrocyte activation at late phase of EAE.

Role of FABP7 in tumor cell signaling

Lipids are major molecules for the function of organisms and are involved in the pathophysiology of various diseases. Fatty acids (FAs) signaling and their metabolism are some of the most important pathways in tumor development, as lipids serve as energetic sources during carcinogenesis. Fatty acid binding proteins (FABPs) facilitate FAs transport to different cell organelles, modulating their metabolism along with mediating other physiological activities. FABP7, brain-typed FABP, is thought to be an important molecule for cell proliferation in healthy as well as diseased organisms. Several studies on human tumors and tumor-derived cell lines put FABP7 in the center of tumorigenesis, and its high expression level has been reported to correlate with poor prognosis in different tumor types. Several types of FABP7-expressing tumors have shown an up-regulation of cell signaling activity, but molecular mechanisms of FABP7 involvement in tumorigenesis still remain elusive. In this review, we focus on the expression and function of FABP7 in different tumors, and possible mechanisms of FABP7 in tumor proliferation and migration.

Maternal marginal iodine deficiency delays cerebellar Bergmann glial cell development in rat offspring: Involvement of Notch signaling pathway

During early pregnancy, iodine deficiency (ID) is linked to adverse effects on child motor and psychomotor function. Maternal marginal ID has become a common public health problem. It is unclear whether marginal ID influences the development of the cerebellum or its underlying mechanisms. Thus, the purpose of this study was to determine the effects of marginal ID on the development of cerebellar Bergmann glial cells (BGs) and investigate the activation of the Notch signaling pathway, which is crucial for the development and morphology of BGs. We treated Wistar rats with an ID diet (iodine content 60 ± 1.5 ng/g) supplemented with deionized water containing different concentrations of potassium iodide (KI) (183, 117, and 0 μg/L for the control, marginal ID, and severe ID groups, respectively) during pregnancy and lactation. We explored the morphology of the BGs by Golgi-Cox staining and immunofluorescence and investigated the Notch signaling pathway using western blot. Our results showed that the marginal ID and severe ID groups had decreased cerebellar BG fiber lengths (P < 0.05 and 0.01, respectively) and numbers (P < 0.01 for both) on postnatal day (PN) 7, PN14, and PN21 compared to the control group. Moreover, the data showed that severe ID significantly reduced Dll1, Notch1, RBP-Jκ, and BLBP protein levels at all three time points. Marginal ID slightly reduced the expression of Notch1 on PN7 (P < 0.05) and PN21 (P < 0.01), RBP-Jκ on PN14 (P < 0.01) and PN21 (P < 0.05), and BLBP on PN7 (P < 0.05). There was no significant difference in Dll1 protein levels between the marginal ID and control groups at any time point. Our study suggests that marginal ID leads to mild damage to BG morphogenesis in the cerebellum. The abnormal regulation of the Notch signaling pathway may be involved in the damage to BGs.

Down-regulation of fatty acid binding protein 7 (Fabp7) is a hallmark of the postpartum brain

Fatty acid binding protein 7 (Fabp7) is a versatile protein that is linked to glial differentiation and proliferation, neurogenesis, and multiple mental health disorders. Recent microarray studies identified a robust decrease in Fabp7 expression in key brain regions of the postpartum rodents. Given its diverse functions, Fabp7 could play a critical role in sculpting the maternal brain and promoting the maternal phenotype. The present study aimed at investigating the expression profile of Fabp7 across the postpartum CNS. Quantitative real-time PCR (qPCR) analysis showed that Fabp7 mRNA was consistently down-regulated across the postpartum brain. Of the 9 maternal care-related regions tested, seven exhibited significant decreases in Fabp7 in postpartum (relative to virgin) females, including medial prefrontal cortex (mPFC), nucleus accumbens (NA), lateral septum (LS), bed nucleus of stria terminalis dorsal (BnSTd), paraventricular nucleus (PVN), lateral hypothalamus (LH), and basolateral and central amygdala (BLA/CeA). For both ventral tegmental area (VTA) and medial preoptic area (MPOA) levels of Fabp7 were lower in mothers, but levels of changes did not reach significance. Confocal microscopy revealed that protein expression of Fabp7 in the LS paralleled mRNA findings. Specifically, the caudal LS exhibited a significant reduction in Fabp7 immunoreactivity, while decreases in medial LS were just above significance. Double fluorescent immunolabeling confirmed the astrocytic phenotype of Fabp7-expressing cells. Collectively, this research demonstrates a broad and marked reduction in Fabp7 expression in the postpartum brain, suggesting that down-regulation of Fabp7 may serve as a hallmark of the postpartum brain and contribute to the maternal phenotype.

Pax6-dependent regulation of the rat Fabp7 promoter activity

Fabp7 gene encodes a brain-specific fatty acid-binding protein that is widely used as a marker for neural stem cells. Here, we report that the activity of rat Fabp7 promoter was regulated directly by a transcription factor, Pax6. Deletion analyses identified an essential region (-837 to -64 from transcription start site) in the rat Fabp7 promoter. This region controls promoter activity in rat embryos and in the mouse cultured cell line MEB5. Over-expressing wild-type Pax6 or a dominant-negative Pax6 mutant enhanced and suppressed, respectively, the promoter activity. Pax6 can bind the region directly, although the region contains no clear binding motif for Pax6. The rat Fabp7 promoter also contains conserved binding sites for Pbx/POU (-384 to -377) and CBF1 (-270 to -262). However, specific deletion of the sites showed no significant reduction in the promoter activity, although a gel mobility shift assay confirmed that CBF1 binds the conserved sequence. Taken together, these results suggest that the rat Fabp7 promoter is mainly regulated by Pax6. The Pax6-dependent regulation of the rat Fabp7 expression might have an evolutionary aspect between rat and mouse; the former may need to efficiently use fatty acids to make the brain bigger than the latter.

Spinal Cord Stem Cells In Their Microenvironment: The Ependyma as a Stem Cell Niche

The ependyma of the spinal cord is currently proposed as a latent neural stem cell niche. This chapter discusses recent knowledge on the developmental origin and nature of the heterogeneous population of cells that compose this stem cell microenviroment, their diverse physiological properties and regulation. The chapter also reviews relevant data on the ependymal cells as a source of plasticity for spinal cord repair.

Molecular components and polarity of radial glial cells during cerebral cortex development

Originating from ectodermal epithelium, radial glial cells (RGCs) retain apico-basolateral polarity and comprise a pseudostratified epithelial layer in the developing cerebral cortex. The apical endfeet of the RGCs faces the fluid-filled ventricles, while the basal processes extend across the entire cortical span towards the pial surface. RGC functions are largely dependent on this polarized structure and the molecular components that define it. In this review, we will dissect existing molecular evidence on RGC polarity establishment and during cerebral cortex development and provide our perspective on the remaining key questions.

Eml1 loss impairs apical progenitor spindle length and soma shape in the developing cerebral cortex

The ventricular zone (VZ) of the developing cerebral cortex is a pseudostratified epithelium that contains progenitors undergoing precisely regulated divisions at its most apical side, the ventricular lining (VL). Mitotic perturbations can contribute to pathological mechanisms leading to cortical malformations. The HeCo mutant mouse exhibits subcortical band heterotopia (SBH), likely to be initiated by progenitor delamination from the VZ early during corticogenesis. The causes for this are however, currently unknown. Eml1, a microtubule (MT)-associated protein of the EMAP family, is impaired in these mice. We first show that MT dynamics are perturbed in mutant progenitor cells in vitro. These may influence interphase and mitotic MT mechanisms and indeed, centrosome and primary cilia were altered and spindles were found to be abnormally long in HeCo progenitors. Consistently, MT and spindle length regulators were identified in EML1 pulldowns from embryonic brain extracts. Finally, we found that mitotic cell shape is also abnormal in the mutant VZ. These previously unidentified VZ characteristics suggest altered cell constraints which may contribute to cell delamination.

Propofol Exposure in Early Life Induced Developmental Impairments in the Mouse Cerebellum

Propofol is a widely used anesthetic in the clinic while several studies have demonstrated that propofol exposure may cause neurotoxicity in the developing brain. However, the effects of early propofol exposure on cerebellar development are not well understood. Propofol (30 or 60 mg/kg) was administered to mice on postnatal day (P)7; Purkinje cell dendritogenesis and Bergmann glial cell development were evaluated on P8, and granule neuron migration was analyzed on P10. The results indicated that exposure to propofol on P7 resulted in a significant reduction in calbindin-labeled Purkinje cells and their dendrite length. Furthermore, propofol induced impairments in Bergmann glia development, which might be involved in the delay of granule neuron migration from the external granular layer (EGL) to the internal granular layer (IGL) during P8 to P10 at the 60 mg/kg dosage, but not at the 30 mg/kg dosage. Several reports have suggested that the Notch signaling pathway plays instructive roles in the morphogenesis of Bergmann glia. Here, it was revealed that propofol treatment decreased Jagged1 and Notch1 protein levels in the cerebellum on P8. Taken together, exposure to propofol during the neonatal period impairs Bergmann glia development and may therefore lead to cerebellum development defects. Our results may aid in the understanding of the neurotoxic effects of propofol when administrated to infants.

The Role of Lipid Metabolism for Neural Stem Cell Regulation

Neural stem/progenitor cells (NSPCs) give rise to billions of cells during development and are critical for proper brain formation. The finding that NSPCs persist throughout adulthood has challenged the view that the brain has poor regenerative abilities and raised hope for stem cell-based regenerative therapies. For decades there has been a strong movement towards understanding the requirements of NSPCs and their regulation, resulting in the discovery of many transcription factors and signaling pathways that can influence NSPC behavior and neurogenesis. However, the role of metabolism for NSPC regulation has only gained attention recently. Lipid metabolism in particular has been shown to influence proliferation and neurogenesis, offering exciting new possible mechanisms of NSPC regulation, as lipids are not only the building blocks of membranes, but can also act as alternative energy sources and signaling entities. Here I review the recent literature examining the role of lipid metabolism for NSPC regulation and neurogenesis.

Increased population of immature enteric glial cells in the resected proximal ganglionic bowel of Hirschsprung's disease patients

BACKGROUND

Enteric glial cells are essential for normal gastrointestinal function. Abnormalities in glial structure, development, or function lead to disturbances in gastrointestinal physiology. Fatty acid-binding protein 7 (FABP7) is a marker of immature enteric glial cells, whereas S100 is expressed only by mature glial cells. Patients with Hirschsprung's disease (HSCR) often suffer from dysmotility and enterocolitis despite proper surgery. We designed this study to determine the distribution and expression of glial cells in patients with HSCR compared to normal controls.

METHODS

We investigated FABP7, S100, and PGP 9.5 expressions in both the ganglionic and aganglionic bowel of patients with HSCR (n = 6) versus normal control colon (n = 6). Protein distribution was assessed by using immunofluorescence and confocal microscopy. Gene and protein expressions were quantified using quantitative real-time polymerase chain reaction (qPCR), Western blot analysis, and densitometry.

RESULTS

qPCR and Western blot analysis demonstrated a significantly increased FABP7 expression in ganglionic specimens compared to control specimen (P < 0.05). Confocal microscopy revealed FABP7⁺ glia cells lie under the colonic epithelium and in close apposition to enteric neurons in the ganglionic bowel.

CONCLUSIONS

The significantly increased number of immature enteric glial cells (EGCs) in the ganglionic bowel of HSCR patients may have adverse effect on the function of enteric neurons and intestinal barrier and thus predispose these patients to intestinal motility problems and enterocolitis.

Dentate granule progenitor cell properties are rapidly altered soon after birth

Neurogenesis occurs during the embryonic period and ceases soon after birth in the neocortex, but continues to occur in the hippocampus even in the adult. The embryonic neocortex has radial glia or progenitor cells expressing brain lipid-binding protein (BLBP), whereas the adult hippocampus has radial granule progenitor cells expressing BLBP and glial fibrillary acidic protein (GFAP) in the subgranular zone. We previously found that embryonic hippocampal granule progenitor cells express GFAP, but not BLBP, indicating that these cells are different from both embryonic neocortical and adult granule progenitor cells. In the present study, as the first step towards understanding the mechanism of persistent hippocampal neurogenesis, we aimed to determine the stage at which embryonic-type granule progenitors become adult-type progenitors using mouse Gfap-GFP transgenic mice. During the embryonic stages, Gfap-GFP-positive (Gfap-GFP+) cells were distributed in the entire developing dentate gyrus (DG), whereas BLBP-positive (BLBP+) cells were mainly present in the fimbria and subpial region, and to some extent in the DG. Up to postnatal day 0 (P0), double-positive cells were scarcely detected. However, at P1, one-third of the Gfap-GFP+ cells in the DG suddenly began to weakly express BLBP. Thereafter, Gfap-GFP+/BLBP+ cells rapidly increased in number, and extended their radial processes in the inner granular cell layer. At P14 and in the adult, two-thirds of the Gfap-GFP+ cells in the subgranular zone showed BLBP immunoreactivity. These results suggest that the properties of hippocampal granule progenitor cells are rapidly altered from an embryonic to adult type soon after birth.

Loss of Usp9x disrupts cell adhesion, and components of the Wnt and Notch signaling pathways in neural progenitors

Development of neural progenitors depends upon the coordination of appropriate intrinsic responses to extrinsic signalling pathways. Here we show the deubiquitylating enzyme, Usp9x regulates components of both intrinsic and extrinsic fate determinants. Nestin-cre mediated ablation of Usp9x from embryonic neural progenitors in vivo resulted in a transient disruption of cell adhesion and apical-basal polarity and, an increased number and ectopic localisation of intermediate neural progenitors. In contrast to other adhesion and polarity proteins, levels of β-catenin protein, especially S33/S37/T41 phospho-β-catenin, were markedly increased in Usp9x^−/Y embryonic cortices. Loss of Usp9x altered composition of the β-catenin destruction complex possibly impeding degradation of S33/S37/T41 phospho-β-catenin. Pathway analysis of transcriptomic data identified Wnt signalling as significantly affected in Usp9x^−/Y embryonic brains. Depletion of Usp9x in cultured human neural progenitors resulted in Wnt-reporter activation. Usp9x also regulated components of the Notch signalling pathway. Usp9x co-localized and associated with both Itch and Numb in embryonic neocortices. Loss of Usp9x led to decreased Itch and Numb levels, and a concomitant increase in levels of the Notch intracellular domain as well as, increased expression of the Notch target gene Hes5. Therefore Usp9x modulates and potentially coordinates multiple fate determinants in neural progenitors.

Retinoic acid controls early neurogenesis in the developing mouse cerebral cortex

A tight regulation of neuron production is required to generate a functional cerebral cortex and is achieved by a proper balance between proliferation and differentiation of progenitor cells. Though the vitamin A (retinol) active derivative retinoic acid (RA) has been implicated as one of the signals acting during mammalian forebrain neurogenesis, its function at the onset of neurogenesis as well as during establishment of cortical layers and neuronal subtypes remains elusive. One limitation is that murine mutants for genes encoding key enzymes involved in RA synthesis die during early embryonic development. We analysed corticogenesis in Rdh10 null mutants, in which an RA deficiency is generated as the intracellular retinol to retinaldehyde conversion is abolished. When analysed at the latest stage before lethality occurs (embryonic day [E]13.5), the mutants show smaller telencephalic vesicles and the thickness of their cortical plate is strongly reduced. The first progenitors formed in the cortical plate are radial glial (RG) cells which generate neurons either directly, or through an indirect mechanism involving the production of intermediate neuronal progenitors (INPs) which then give rise to neurons. We show that in absence of RA, the RG progenitors proliferate less and prematurely produce neurons, leading to their depletion at E11.5. Furthermore, we could demonstrate that lack of RA impairs the generation of INPs at E13.5 and affects the cell cycle exit of progenitor cells during corticogenesis, altogether leading to a deficit in projection neurons and to microcephaly.

Derivation of Functional Human Astrocytes from Cerebral Organoids

Astrocytes play a critical role in the development and homeostasis of the central nervous system (CNS). Astrocyte dysfunction results in several neurological and degenerative diseases. However, a major challenge to our understanding of astrocyte physiology and pathology is the restriction of studies to animal models, human post-mortem brain tissues, or samples obtained from invasive surgical procedures. Here, we report a protocol to generate human functional astrocytes from cerebral organoids derived from human pluripotent stem cells. The cellular isolation of cerebral organoids yielded cells that were morphologically and functionally like astrocytes. Immunolabelling and proteomic assays revealed that human organoid-derived astrocytes express the main astrocytic molecular markers, including glutamate transporters, specific enzymes and cytoskeletal proteins. We found that organoid-derived astrocytes strongly supported neuronal survival and neurite outgrowth and responded to ATP through transient calcium wave elevations, which are hallmarks of astrocyte physiology. Additionally, these astrocytes presented similar functional pathways to those isolated from adult human cortex by surgical procedures. This is the first study to provide proteomic and functional analyses of astrocytes isolated from human cerebral organoids. The isolation of these astrocytes holds great potential for the investigation of developmental and evolutionary features of the human brain and provides a useful approach to drug screening and neurodegenerative disease modelling.

Molecular Diversity of Midbrain Development in Mouse, Human, and Stem Cells

Understanding human embryonic ventral midbrain is of major interest for Parkinson's disease. However, the cell types, their gene expression dynamics, and their relationship to commonly used rodent models remain to be defined. We performed single-cell RNA sequencing to examine ventral midbrain development in human and mouse. We found 25 molecularly defined human cell types, including five subtypes of radial glia-like cells and four progenitors. In the mouse, two mature fetal dopaminergic neuron subtypes diversified into five adult classes during postnatal development. Cell types and gene expression were generally conserved across species, but with clear differences in cell proliferation, developmental timing, and dopaminergic neuron development. Additionally, we developed a method to quantitatively assess the fidelity of dopaminergic neurons derived from human pluripotent stem cells, at a single-cell level. Thus, our study provides insight into the molecular programs controlling human midbrain development and provides a foundation for the development of cell replacement therapies.

NOTCH1 and SOX10 are Essential for Proliferation and Radiation Resistance of Cancer Stem-Like Cells in Adenoid Cystic Carcinoma

PURPOSE

Although the existence of cancer stem cells (CSC) in adenoid cystic carcinoma (ACC) has been proposed, lack of assays for their propagation and uncertainty about molecular markers prevented their characterization. Our objective was to isolate CSC from ACC and provide insight into signaling pathways that support their propagation.

EXPERIMENTAL DESIGN

To isolate CSC from ACC and characterize them, we used ROCK inhibitor-supplemented cell culture, immunomagnetic cell sorting, andin vitro/in vivoassays for CSC viability and tumorigenicity.

RESULTS

We identified in ACC CD133-positive CSC that expressed NOTCH1 and SOX10, formed spheroids, and initiated tumors in nude mice. CD133(+)ACC cells produced activated NOTCH1 (N1ICD) and generated CD133(-)cells that expressed JAG1 as well as neural differentiation factors NR2F1, NR2F2, and p27Kip1. Knockdowns ofNOTCH1, SOX10, and their common effectorFABP7had negative effects on each other, inhibited spheroidogenesis, and induced cell death pointing at their essential roles in CSC maintenance. Downstream effects ofFABP7knockdown included suppression of a broad spectrum of genes involved in proliferation, ribosome biogenesis, and metabolism. Among proliferation-linked NOTCH1/FABP7 targets, we identified SKP2 and its substrate p27Kip1. A γ-secretase inhibitor, DAPT, selectively depleted CD133(+)cells, suppressed N1ICD and SKP2, induced p27Kip1, inhibited ACC growthin vivo, and sensitized CD133(+)cells to radiation.

CONCLUSIONS

These results establish in the majority of ACC the presence of a previously uncharacterized population of CD133(+)cells with neural stem properties, which are driven by SOX10, NOTCH1, and FABP7. Sensitivity of these cells to Notch inhibition and their dependence on SKP2 offer new opportunities for targeted ACC therapies.

Clinical and molecular insights into adenoid cystic carcinoma: Neural crest-like stemness as a target

OBJECTIVES

This review surveys trialed therapies and molecular defects in adenoid cystic carcinoma (ACC), with an emphasis on neural crest-like stemness characteristics of newly discovered cancer stem cells (CSCs) and therapies that may target these CSCs.

DATA SOURCES

Articles available on Pubmed or OVID MEDLINE databases and unpublished data.

REVIEW METHODS

Systematic review of articles pertaining to ACC and neural crest-like stem cells.

RESULTS

Adenoid cystic carcinoma of the salivary gland is a slowly growing but relentless cancer that is prone to nerve invasion and metastases. A lack of understanding of molecular etiology and absence of targetable drivers has limited therapy for patients with ACC to surgery and radiation. Currently, no curative treatments are available for patients with metastatic disease, which highlights the need for effective new therapies. Research in this area has been inhibited by the lack of validated cell lines and a paucity of clinically useful markers. The ACC research environment has recently improved, thanks to the introduction of novel tools, technologies, approaches, and models. Improved understanding of ACC suggests that neural crest-like stemness is a major target in this rare tumor. New cell culture techniques and patient-derived xenografts provide tools for preclinical testing.

CONCLUSION

Preclinical research has not identified effective targets in ACC, as confirmed by the large number of failed clinical trials. New molecular data suggest that drivers of neural crest-like stemness may be required for maintenance of ACC; as such, CSCs are a target for therapy of ACC.

Astroglial Cells in Development, Regeneration, and Repair

Three main cellular components have been described in the CNS: neurons, astrocytes, and oligodendrocytes. In the past 10 years, lineage studies first based on retroviruses in the embryonic CNS and then by genetic fate mapping in both the prenatal and postnatal CNS have proposed that astroglial cells can be progenitors for neurons and oligodendrocytes. Hence, the population of astroglial cells is increasingly recognized as heterogeneous and diverse, encompassing cell types performing widely different roles in development and plasticity. Astroglial cells populating the neurogenic niches increase their proliferation after perinatal injury and in young mice can differentiate into neurons and oligodendrocytes that migrate to the cerebral cortex, replacing the cells that are lost. Although much remains to be learned about this process, it appears that the up-regulation of the Fibroblast growth factor receptor is critical for mediating the injury-induced increase in cell division and perhaps for the neuronal differentiation of astroglial cells. NEUROSCIENTIST 13(2):173—185, 2007.

Cortical Structure Alterations and Social Behavior Impairment in p50-Deficient Mice

Alterations in genes that regulate neurodevelopment can lead to cortical malformations, resulting in malfunction during postnatal life. The NF-κB pathway has a key role during neurodevelopment by regulating the maintenance of the neural progenitor cell pool and inhibiting neuronal differentiation. In this study, we evaluated whether mice lacking the NF-κB p50 subunit (KO) present alterations in cortical structure and associated behavioral impairment. We found that, compared with wild type (WT), KO mice at postnatal day 2 present an increase in radial glial cells, an increase in Reelin protein expression levels, in addition to an increase of specific layer thickness. Moreover, adult KO mice display abnormal columnar organization in the somatosensory cortex, a specific decrease in somatostatin- and parvalbumin-expressing interneurons, altered neurite orientation, and a decrease in Synapsin I protein levels. Concerning behavior, KO mice, in addition to an increase in locomotor and exploratory activity, display impairment in social behaviors, with a reduction in social interaction. Finally, we found that risperidone treatment decreased hyperactivity of KO mice, but had no effect on defective social interaction. Altogether, these data add complexity to a growing body of data, suggesting a link between dysregulation of the NF-κB pathway and neurodevelopmental disorders pathogenesis.

MAZ mediates the cross-talk between CT-1 and NOTCH1 signaling during gliogenesis

Neurons and glia cells are differentiated from neural stem/progenitor cells (NSCs/NPCs) during brain development. Concomitant activation of JAK/STAT and NOTCH1 signaling is required for gliogenesis, a process to generate glia cells to ensure proper brain functions. NOTCH1 signaling is down-regulated during neurogenesis and up-regulated during gliogenesis. However, the underlying mechanism remains elusive. We report here that cardiotrophin-1 (CT-1) activates NOTCH1 signaling through the up-regulation of ADAM10, a rate-limiting factor of NOTCH1 signaling activation. We found that a transcriptional factor, Myc-associated zinc finger protein (MAZ), plays an important role in ADAM10 transcription in response to CT-1 in NPCs. MAZ knockdown inhibits CT-1 stimulated gliogenesis and it can be rescued by over-expressing human NICD. Our results provide a link between NOTCH1 activation and neuronal secreted CT-1, suggesting that CT-1 plays an important role in ensuring the coordinated activation of NOTCH1 signaling during gliogenesis.

Canonical Notch signaling plays an instructive role in auditory supporting cell development

The auditory sensory epithelium, composed of mechano-sensory hair cells (HCs) and highly specialized glial-like supporting cells (SCs), is critical for our ability to detect sound. SCs provide structural and functional support to HCs and play an essential role in cochlear development, homeostasis and repair. Despite their importance, however, surprisingly little is known about the molecular mechanisms guiding SC differentiation. Here, we provide evidence that in addition to its well-characterized inhibitory function, canonical Notch signaling plays a positive, instructive role in the differentiation of SCs. Using γ-secretase inhibitor DAPT to acutely block canonical Notch signaling, we identified a cohort of Notch-regulated SC-specific genes, with diverse functions in cell signaling, cell differentiation, neuronal innervation and synaptogenesis. We validated the newly identified Notch-regulated genes in vivo using genetic gain (Emx2^Cre/+; Rosa26^N1ICD/+) and loss-of-function approaches (Emx2^Cre/+; Rosa26^DnMAML1/+). Furthermore, we demonstrate that Notch over-activation in the differentiating murine cochlea (Emx2^Cre/+; Rosa26^N1ICD/+) actively promotes a SC-specific gene expression program. Finally, we show that outer SCs –so called Deiters’ cells are selectively lost by prolonged reduction (Emx2^Cre/+; Rosa26^DnMAML1/+/+) or abolishment of canonical Notch signaling (Fgfr3-iCreER; Rbpj^−/Δ), indicating a critical role for Notch signaling in Deiters’ cell development.

Differential thyroid hormone sensitivity of fast cycling progenitors in the neurogenic niches of tadpoles and juvenile frogs

Adult neurogenesis occurs in neural stem cell (NSC) niches where slow cycling stem cells give rise to faster cycling progenitors. In the adult mouse NSC niche thyroid hormone, T3, and its receptor TRα act as a neurogenic switch promoting progenitor cell cycle completion and neuronal differentiation. Little is known about whether and how T3 controls proliferation of differentially cycling cells during xenopus neurogenesis. To address this question, we first used Sox3 as a marker of stem cell and progenitor populations and then applied pulse-chase EdU/IdU incorporation experiments to identify Sox3-expressing slow cycling (NSC) and fast cycling progenitor cells. We focused on the lateral ventricle of Xenopus laevis and two distinct stages of development: late embryonic development (pre-metamorphic) and juvenile frogs (post-metamorphic). These stages were selected for their relatively stable thyroid hormone availability, either side of the major dynamic phase represented by metamorphosis. TRα expression was found in both pre and post-metamorphic neurogenic regions. However, exogenous T3 treatment only increased proliferation of the fast cycling Sox3+ cell population in post-metamorphic juveniles, having no detectable effect on proliferation in pre-metamorphic tadpoles. We hypothesised that the resistance of proliferative cells to exogenous T3 in pre-metamorphic tadpoles could be related to T3 inactivation by the inactivating Deiodinase 3 enzyme. Expression of dio3 was widespread in the tadpole neurogenic niche, but not in the juvenile neurogenic niche. Use of a T3-reporter transgenic line showed that in juveniles, T3 had a direct transcriptional effect on rapid cycling progenitors. Thus, the fast cycling progenitor cells in the neurogenic niche of tadpoles and juvenile frogs respond differentially to T3 as a function of developmental stage.

Astrocyte-expressed FABP7 regulates dendritic morphology and excitatory synaptic function of cortical neurons

Fatty acid binding protein 7 (FABP7) expressed by astrocytes in developing and mature brains is involved in uptake and transportation of fatty acids, signal transduction, and gene transcription. Fabp7 knockout (Fabp7 KO) mice show behavioral phenotypes reminiscent of human neuropsychiatric disorders such as schizophrenia. However, direct evidence showing how FABP7 deficiency in astrocytes leads to altered brain function is lacking. Here, we examined neuronal dendritic morphology and synaptic plasticity in medial prefrontal cortex (mPFC) of Fabp7 KO mice and in primary cortical neuronal cultures. Golgi staining of cortical pyramidal neurons in Fabp7 KO mice revealed aberrant dendritic morphology and decreased spine density compared with those in wild-type (WT) mice. Aberrant dendritic morphology was also observed in primary cortical neurons co-cultured with FABP7-deficient astrocytes and neurons cultured in Fabp7 KO astrocyte-conditioned medium. Excitatory synapse number was decreased in mPFC of Fabp7 KO mice and in neurons co-cultured with Fabp7 KO astrocytes. Accordingly, whole-cell voltage-clamp recording in brain slices from pyramidal cells in the mPFC showed that both amplitude and frequency of action potential-independent miniature excitatory postsynaptic currents (mEPSCs) were decreased in Fabp7 KO mice. Moreover, transplantation of WT astrocytes into the mPFC of Fabp7 KO mice partially attenuated behavioral impairments. Collectively, these results suggest that astrocytic FABP7 is important for dendritic arbor growth, neuronal excitatory synapse formation, and synaptic transmission, and provide new insights linking FABP7, lipid homeostasis, and neuropsychiatric disorders, leading to novel therapeutic interventions.

Heterogeneity and Bipotency of Astroglial-Like Cerebellar Progenitors along the Interneuron and Glial Lineages

Cerebellar GABAergic interneurons in mouse comprise multiple subsets of morphologically and neurochemically distinct phenotypes located at strategic nodes of cerebellar local circuits. These cells are produced by common progenitors deriving from the ventricular epithelium during embryogenesis and from the prospective white matter (PWM) during postnatal development. However, it is not clear whether these progenitors are also shared by other cerebellar lineages and whether germinative sites different from the PWM originate inhibitory interneurons. Indeed, the postnatal cerebellum hosts another germinal site along the Purkinje cell layer (PCL), in which Bergmann glia are generated up to first the postnatal weeks, which was proposed to be neurogenic. Both PCL and PWM comprise precursors displaying traits of juvenile astroglia and neural stem cell markers. First, we examine the proliferative and fate potential of these niches, showing that different proliferative dynamics regulate progenitor amplification at these sites. In addition, PCL and PWM differ in the generated progeny. GABAergic interneurons are produced exclusively by PWM astroglial-like progenitors, whereas PCL precursors produce only astrocytes. Finally, through in vitro, ex vivo, and in vivo clonal analyses we provide evidence that the postnatal PWM hosts a bipotent progenitor that gives rise to both interneurons and white matter astrocytes.

MicroRNA-mediated non-cell-autonomous regulation of cortical radial glial transformation revealed by a Dicer1 knockout mouse model

Radial glia (RG), as neurogenic progenitors and neuronal migration scaffolds, play critical roles during cortical neurogenesis. RG transformation into astrocytes, marking the transition from developmental to physiological function of these cells, is an important step during cortical development. In this study, we aim to determine the roles of microRNAs (miRNAs) during this biological process. In a conditional Dicer1-null mouse where Dicer1 is deleted in both RG and their neuronal progeny, we observe delayed RG transformation as revealed by the persistence of their radial processes, and reduced number and complexity of translocated RG cell bodies in the postnatal cerebral cortex. Downregulation of Notch1 signaling is crucial to RG transformation, and consistently we find that Notch1 signaling is enhanced in the Dicer1-null cerebral cortex. In addition, we show that, among the Notch1 ligands, Jagged2 (Jag2) is preferentially upregulated in the postnatal Dicer1-null cerebral cortex as well as primary embryonic cortical cultures with instant Dicer1 deletion. Functionally, Dicer1-deleted postnatal cerebellar cells with elevated Jag2 expression stimulate a stronger Notch1 signaling in a RG clone L2.3 when co-cultured than control cells. Therefore, we unravel a novel non-cell-autonomous mechanism that regulates RG transformation by modulating Notch1 signaling via miRNA-mediated suppression of the Nocth1 ligand Jag2. Furthermore, we validate Jag2 as a miR-124 target gene and demonstrate in vitro that Jag2 expression is highly sensitive to Dicer1 deletion. Finally, we propose a new concept of MiRNA-Sensitive target genes, identification of which may unravel a unique mode of miRNA-mediated gene expression regulation.