Activated Notch2 signaling inhibits differentiation of cerebellar granule neuron precursors by maintaining proliferation

MiR-326: Role and significance in brain cancers

MicroRNAs (miRNAs) are small non-coding RNAs that act as critical regulators of gene expression by repressing mRNA translation. The role of miRNAs in cell physiology spans from cell cycle control to cell proliferation and differentiation, both during development and in adult tissues. Accordingly, dysregulated expression of miRNAs has been reported in several diseases, including cancer, where miRNAs can act as oncogenes or oncosuppressors. Of note, miRNA signatures are also under investigation for classification, diagnosis, and prognosis of cancer patients. Brain tumours are primarily associated with poor prognosis and high mortality, highlighting an urgent need for novel diagnostic, prognostic, and therapeutic tools. Among miRNAs investigated in brain tumours, miR-326 has been shown to act as a tumour suppressor in adult and paediatric brain cancers. In this review, we describe the role of miR-326 in malignant as well as benign cancers originating from brain tissue. In addition, since miR-326 expression can be regulated by other non-coding RNA species, adding a further layer of regulation in the cancer-promoting axis, we discuss this miRNA's role in targeted therapy for brain cancers.

Low-Density Primary Cell Culture of Postnatal Murine Cerebellar Progenitors In Vitro

Cerebellum is the major player of motor functions of the body, as well as being involved in plenty of nonmotor behavior traits. There are numerous disorders related to cerebellum that have severe consequences for patients and the absence of an effective treatment, so it is crucial to emphasize conducting research directed to deeply understand the biology of this structure, giving special importance to stem cells that could have regenerative potential. Here, we describe a novel protocol for isolating neural stem cells from postnatal mouse cerebellum, allowing for the study of progenitor cells from three distinct proliferative niches. Cells are maintained in low-density cultures without external growth factors, facilitating the study of intrinsic programming. We also suggest numerous applications that could provide an insight into the identity, development, and behavior of progenitor cells, which may contribute to the development of treatments for cerebellar disorders.

Cerebellar granular neuron progenitors exit their germinative niche via BarH-like1 activity mediated partly by inhibition of T-cell factor

Cerebellar granule neuron progenitors (GNPs) originate from the upper rhombic lip (URL), a germinative niche in which developmental defects produce human diseases. T-cell factor (TCF) responsiveness and Notch dependence are hallmarks of self-renewal in neural stem cells. TCF activity, together with transcripts encoding proneural gene repressors hairy and enhancer of split (Hes/Hey), are detected in the URL; however, their functions and regulatory modes are undeciphered. Here, we established amphibian as a pertinent model for studying vertebrate URL development. The amphibian long-lived URL is TCF active, whereas the external granular layer (EGL) is non-proliferative and expresses hes4 and hes5 genes. Using functional and transcriptomic approaches, we show that TCF activity is necessary for URL emergence and maintenance. We establish that the transcription factor Barhl1 controls GNP exit from the URL, acting partly through direct TCF inhibition. Identification of Barhl1 target genes suggests that, besides TCF, Barhl1 inhibits transcription of hes5 genes independently of Notch signaling. Observations in amniotes suggest a conserved role for Barhl in maintenance of the URL and/or EGL via co-regulation of TCF, Hes and Hey genes.

Human iPSC modeling recapitulates in vivo sympathoadrenal development and reveals an aberrant developmental subpopulation in familial neuroblastoma

Studies defining normal and disrupted human neural crest cell development have been challenging given its early timing and intricacy of development. Consequently, insight into the early disruptive events causing a neural crest related disease such as pediatric cancer neuroblastoma is limited. To overcome this problem, we developed an in vitro differentiation model to recapitulate the normal in vivo developmental process of the sympathoadrenal lineage which gives rise to neuroblastoma. We used human in vitro pluripotent stem cells and single-cell RNA sequencing to recapitulate the molecular events during sympathoadrenal development. We provide a detailed map of dynamically regulated transcriptomes during sympathoblast formation and illustrate the power of this model to study early events of the development of human neuroblastoma, identifying a distinct subpopulation of cell marked by SOX2 expression in developing sympathoblast obtained from patient derived iPSC cells harboring a germline activating mutation in the anaplastic lymphoma kinase (ALK) gene.

Regulation of early cerebellar development

The study of cerebellar development has been at the forefront of neuroscience since the pioneering work of Wilhelm His Sr., Santiago Ramón y Cajal and many others since the 19th century. They laid the foundation to identify the circuitry of the cerebellum, already revealing its stereotypic three-layered cortex and discerning several of its neuronal components. Their work was fundamental in the acceptance of the neuron doctrine, which acknowledges the key role of individual neurons in forming the basic units of the nervous system. Increasing evidence shows that the cerebellum performs a variety of homeostatic and higher order neuronal functions beyond the mere control of motor behaviour. Over the last three decades, many studies have revealed the molecular machinery that regulates distinct aspects of cerebellar development, from the establishment of a cerebellar anlage in the posterior brain to the identification of cerebellar neuron diversity at the single cell level. In this review, we focus on summarizing our current knowledge on early cerebellar development with a particular emphasis on the molecular determinants that secure neuron specification and contribute to the diversity of cerebellar neurons.

Placental DNA methylation profile as predicting marker for autism spectrum disorder (ASD)

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that impairs normal brain development and socio-cognitive abilities. The pathogenesis of this condition points out the involvement of genetic and environmental factors during in-utero life. Placenta, as an interface tissue between mother and fetus, provides developing fetus requirements and exposes it to maternal environment as well. Therefore, the alteration of DNA methylation as epigenetic consequence of gene-environmental interaction in the placenta could shed light on ASD pathogenesis. In this study, we reviewed the current findings on placental methylation status and its association with ASD. Differentially methylated regions (DMRs) in ASD-developing placenta were found to be mainly enriched in ASD gene loci affecting synaptogenesis, microtubule dynamics, neurogenesis and neuritogenesis. In addition, non-genic DMRs in ASD-placenta proposes an alternative contributing mechanism for ASD development. Our study highlights the importance of placental DNA methylation signature as a biomarker for ASD prediction.

Dissociation of Cerebellar Granule Neuron Progenitors for Culture, FACS, Transcriptomics, and Molecular Biology

Brain growth reflects the proliferation dynamics of neural progenitors, and understanding brain growth requires molecular, genetic, and functional studies of these specific cells. Cerebellar granule neuron progenitors (CGNPs) proliferate in the early postnatal period in both mice and humans, to generate the largest population of neurons in the central nervous system. CGNPs present a large, spatially segregated source of neural progenitors with a consistent, well-characterized temporal pattern of proliferation and differentiation that facilitates analysis. Dissociating of CGNPs with the methods below will generate a suspension of primary neural progenitors harvested from the postnatal brain that may be used for diverse experimental analyses including cell culture, protein extraction, flow cytometry, metabolomic analysis, and transcriptomic analysis with single-cell resolution (scRNA-seq).

Cerebellar development after preterm birth

Preterm birth and its complications and the associated adverse factors, including brain hemorrhage, inflammation, and the side effects of medical treatments, are the leading causes of neurodevelopmental disability. Growing evidence suggests that preterm birth affects the cerebellum, which is the brain region involved in motor coordination, cognition, learning, memory, and social communication. The cerebellum is particularly vulnerable to the adverse effects of preterm birth because key cerebellar developmental processes, including the proliferation of neural progenitors, and differentiation and migration of neurons, occur in the third trimester of a human pregnancy. This review discusses the negative impacts of preterm birth and its associated factors on cerebellar development, focusing on the cellular and molecular mechanisms that mediate cerebellar pathology. A better understanding of the cerebellar developmental mechanisms affected by preterm birth is necessary for developing novel treatment and neuroprotective strategies to ameliorate the cognitive, behavioral, and motor deficits experienced by preterm subjects.

Cerebellum lineage allocation, morphogenesis and repair: impact of interplay amongst cells

The cerebellum has a simple cytoarchitecture consisting of a folded cortex with three cell layers that surrounds a nuclear structure housing the output neurons. The excitatory neurons are generated from a unique progenitor zone, the rhombic lip, whereas the inhibitory neurons and astrocytes are generated from the ventricular zone. The growth phase of the cerebellum is driven by lineage-restricted progenitor populations derived from each zone. Research during the past decade has uncovered the importance of cell-to-cell communication between the lineages through largely unknown signaling mechanisms for regulating the scaling of cell numbers and cell plasticity during mouse development and following injury in the neonatal (P0-P14) cerebellum. This Review focuses on how the interplay between cell types is key to morphogenesis, production of robust neural circuits and replenishment of cells after injury, and ends with a discussion of the implications of the greater complexity of the human cerebellar progenitor zones for development and disease.

Glyphosate-based herbicide induces long-lasting impairment in neuronal and glial differentiation

Glyphosate-based herbicides (GBH) are among the most sold pesticides in the world. There are several formulations based on the active ingredient glyphosate (GLY) used along with other chemicals to improve the absorption and penetration in plants. The final composition of commercial GBH may modify GLY toxicological profile, potentially enhancing its neurotoxic properties. The developing nervous system is particularly susceptible to insults occurring during the early phases of development, and exposure to chemicals in this period may lead to persistent impairments on neurogenesis and differentiation. The aim of this study was to evaluate the long-lasting effects of a sub-cytotoxic concentration, 2.5 parts per million of GBH and GLY, on the differentiation of human neuroepithelial stem cells (NES) derived from induced pluripotent stem cells (iPSC). We treated NES cells with each compound and evaluated the effects on key cellular processes, such as proliferation and differentiation in daughter cells never directly exposed to the toxicants. We found that GBH induced a more immature neuronal profile associated to increased PAX6, NESTIN and DCX expression, and a shift in the differentiation process toward glial cell fate at the expense of mature neurons, as shown by an increase in the glial markers GFAP, GLT1, GLAST and a decrease in MAP2. Such alterations were associated to dysregulation of key genes critically involved in neurogenesis, including PAX6, HES1, HES5, and DDK1. Altogether, the data indicate that subtoxic concentrations of GBH, but not of GLY, induce long-lasting impairments on the differentiation potential of NES cells.

Neuronal Polarity Pathways as Central Integrators of Cell-Extrinsic Information During Interactions of Neural Progenitors With Germinal Niches

Germinal niche interactions and their effect on developing neurons have become the subject of intense investigation. Dissecting the complex interplay of cell-extrinsic and cell-intrinsic factors at the heart of these interactions reveals the critical basic mechanisms of neural development and how it goes awry in pediatric neurologic disorders. A full accounting of how developing neurons navigate their niches to mature and integrate into a developing neural circuit requires a combination of genetic characterization of and physical access to neurons and their supporting cell types plus transformative imaging to determine the cell biological and gene-regulatory responses to niche cues. The mouse cerebellar cortex is a prototypical experimental system meeting all of these criteria. The lessons learned therein have been scaled to other model systems and brain regions to stimulate discoveries of how developing neurons make many developmental decisions. This review focuses on how mouse cerebellar granule neuron progenitors interact with signals in their germinal niche and how that affects the neuronal differentiation and cell polarization programs that underpin lamination of the developing cerebellum. We show how modeling of these mechanisms in other systems has added to the growing evidence of how defective neuronal polarity contributes to developmental disease.

Conserved exchange of paralog proteins during neuronal differentiation

Paralog proteins promote fine tuning of protein complexes. The author identified a specific paralog signature conserved across vertebrate neuronal differentiation. Altering the ratio of SEC23 paralogs in the COPII complex influences neuronal differentiation in a opposite way.

Gene duplication enables the emergence of new functions by lowering the evolutionary pressure that is posed on the ancestral genes. Previous studies have highlighted the role of specific paralog genes during cell differentiation, for example, in chromatin remodeling complexes. It remains unexplored whether similar mechanisms extend to other biological functions and whether the regulation of paralog genes is conserved across species. Here, we analyze the expression of paralogs across human tissues, during development and neuronal differentiation in fish, rodents and humans. Whereas ∼80% of paralog genes are co-regulated, a subset of paralogs shows divergent expression profiles, contributing to variability of protein complexes. We identify 78 substitutions of paralog pairs that occur during neuronal differentiation and are conserved across species. Among these, we highlight a substitution between the paralogs SEC23A and SEC23B members of the COPII complex. Altering the ratio between these two genes via RNAi-mediated knockdown is sufficient to influence neuron differentiation. We propose that remodeling of the vesicular transport system via paralog substitutions is an evolutionary conserved mechanism enabling neuronal differentiation.

The First 50 Years of Postnatal Neurogenesis in the Cerebellum: a Long Journey Across Phenomena, Mechanisms, and Human Disease

The discovery by Altman and coworkers of adult-born microneurons in the olfactory bulb and dentate gyrus has triggered a long stream of studies and many attempts to harness adult neurogenesis, promote regeneration after injury, and contrast cognitive decline in the elderly. Likewise, the discovery of postnatal neurogenesis in the cerebellum has provided the framework for many subsequent molecular studies, including investigations of developmental processes and the assessment of GC progenitor (GCP) clonal expansion in the context of human disease. Here, I will briefly discuss some of the discoveries made in the field of cerebellar development over the years building upon the findings of Altman and his colleagues, touching upon signaling pathways that regulate granule cell neurogenesis and their involvement in developmental and neoplastic disorders of the cerebellum.

Excitotoxic stimulation activates distinct pathogenic and protective expression signatures in the hippocampus

Excitotoxic events underlying ischaemic and traumatic brain injuries activate degenerative and protective pathways, particularly in the hippocampus. To understand opposing pathways that determine the brain's response to excitotoxicity, we used hippocampal explants, thereby eliminating systemic variables during a precise protocol of excitatory stimulation. N‐methyl‐d‐aspartate (NMDA) was applied for 20 min and total RNA isolated one and 24 h later for neurobiology‐specific microarrays. Distinct groups of genes exhibited early vs. delayed induction, with 63 genes exclusively reduced 24‐h post‐insult. Egr‐1 and NOR‐1 displayed biphasic transcriptional modulation: early induction followed by delayed suppression. Opposing events of NMDA‐induced genes linked to pathogenesis and cell survival constituted the early expression signature. Delayed degenerative indicators (up‐regulated pathogenic genes, down‐regulated pro‐survival genes) and opposing compensatory responses (down‐regulated pathogenic genes, up‐regulated pro‐survival genes) generated networks with temporal gene profiles mirroring coexpression network clustering. We then used the expression profiles to test whether NF‐κB, a potent transcription factor implicated in both degenerative and protective pathways, is involved in the opposing responses. The NF‐κB inhibitor MG‐132 indeed altered NMDA‐mediated transcriptional changes, revealing components of opposing expression signatures that converge on the single response element. Overall, this study identified counteracting avenues among the distinct responses to excitotoxicity, thereby suggesting multi‐target treatment strategies and implications for predictive medicine.

Shh-Mediated Increase in β-Catenin Levels Maintains Cerebellar Granule Neuron Progenitors in Proliferation

Cerebellar granule neuron progenitors (CGNPs) give rise to the cerebellar granule neurons in the developing cerebellum. Generation of large number of these neurons is made possible by the high proliferation rate of CGNPs in the external granule layer (EGL) in the dorsal cerebellum. Here, we show that upregulation of β-catenin can maintain murine CGNPs in a state of proliferation. Further, we show that β-catenin mRNA and protein levels can be regulated by the mitogen Sonic hedgehog (Shh). Shh signaling led to an increase in the level of the transcription factor N-myc. N-myc was found to bind the β-catenin promoter, and the increase in β-catenin mRNA and protein levels could be prevented by blocking N-myc upregulation downstream of Shh signaling. Furthermore, blocking Wingless-type MMTV integration site (Wnt) signaling by Wnt signaling pathway inhibitor Dickkopf 1 (Dkk-1) in the presence of Shh did not prevent the upregulation of β-catenin. We propose that in culture, Shh signaling regulates β-catenin expression through N-myc and results in increased CGNP proliferation.

Notch Signaling between Cerebellar Granule Cell Progenitors

Cerebellar granule cells (GCs) are cells which comprise over 50% of the neurons in the entire nervous system. GCs enable the cerebellum to properly regulate motor coordination, learning, and consolidation, in addition to cognition, emotion and language. During GC development, maternal GC progenitors (GCPs) divide to produce not only postmitotic GCs but also sister GCPs. However, the molecular machinery for regulating the proportional production of distinct sister cell types from seemingly uniform GCPs is not yet fully understood. Here we report that Notch signaling creates a distinction between GCPs and leads to their proportional differentiation in mice. Among Notch-related molecules, Notch1, Notch2, Jag1, and Hes1 are prominently expressed in GCPs. In vivo monitoring of Hes1-promoter activities showed the presence of two types of GCPs, Notch-signaling ON and OFF, in the external granule layer (EGL). Single-cell RNA sequencing (scRNA-seq) and in silico analyses indicate that ON-GCPs have more proliferative and immature properties, while OFF-GCPs have opposite characteristics. Overexpression as well as knock-down (KD) experiments using in vivo electroporation showed that NOTCH2 and HES1 are involved cell-autonomously to suppress GCP differentiation by inhibiting NEUROD1 expression. In contrast, JAG1-expressing cells non-autonomously upregulated Notch signaling activities via NOTCH2-HES1 in surrounding GCPs, eventually suppressing their differentiation. These findings suggest that Notch signaling results in the proportional generation of two types of cells, immature and differentiating GCPs, which contributes to the well-organized differentiation of GCs.

Origins, Development, and Compartmentation of the Granule Cells of the Cerebellum

Granule cells (GCs) are the most numerous cell type in the cerebellum and indeed, in the brain: at least 99% of all cerebellar neurons are granule cells. In this review article, we first consider the formation of the upper rhombic lip, from which all granule cell precursors arise, and the way by which the upper rhombic lip generates the external granular layer, a secondary germinal epithelium that serves to amplify the upper rhombic lip precursors. Next, we review the mechanisms by which postmitotic granule cells are generated in the external granular layer and migrate radially to settle in the granular layer. In addition, we review the evidence that far from being a homogeneous population, granule cells come in multiple phenotypes with distinct topographical distributions and consider ways in which the heterogeneity of granule cells might arise during development.

Perinatal exposure to nonylphenol promotes proliferation of granule cell precursors in offspring cerebellum: Involvement of the activation of Notch2 signaling

Nonylphenol (NP), a widely diffused persistent organic pollutant (POP), has been shown to impair cerebellar development and cause cerebellum-dependent behavioral and motor deficits. The precise proliferation of granule cell precursors (GCPs), the source of granular cells (GCs), is required for normal development of cerebellum. Thus, we established an animal model of perinatal exposure to NP, investigated the effect of NP exposure on the cerebellar GCPs proliferation, and explored the potential mechanism involved. Our results showed that perinatal exposure to NP increased cerebellar weight, area, and internal granular cell layer (IGL) thickness in offspring rats. Perinatal exposure to NP also resulted in the GCPs hyperproliferation in the external granular layer (EGL) of the developing cerebellum, which may underlie the above-mentioned cerebellar alterations. However, our results suggested that perinatal exposure to NP had no effects on the length of GCPs proliferation. Meanwhile, perinatal exposure to NP also increased the activation of Notch2 signaling, the regulator of GCPs proliferation. In conclusion, our results supported the idea that exposure to NP caused the hyperproliferation of GCPs in the developing cerebellum. Furthermore, our study also provided the evidence that the activation of Notch2 signaling may be involved in the GCPs hyperproliferation.

Live Imaging Reveals Cerebellar Neural Stem Cell Dynamics and the Role of VNUT in Lineage Progression

Little is known about the intrinsic specification of postnatal cerebellar neural stem cells (NSCs) and to what extent they depend on information from their local niche. Here, we have used an adapted cell preparation of isolated postnatal NSCs and live imaging to demonstrate that cerebellar progenitors maintain their neurogenic nature by displaying hallmarks of NSCs. Furthermore, by using this preparation, all the cell types produced postnatally in the cerebellum, in similar relative proportions to those observed in vivo, can be monitored. The fact that neurogenesis occurs in such organized manner in the absence of signals from the local environment, suggests that cerebellar lineage progression is to an important extent governed by cell-intrinsic or pre-programmed events. Finally, we took advantage of the absence of the niche to assay the influence of the vesicular nucleotide transporter inhibition, which dramatically reduced the number of NSCs in vitro by promoting their progression toward neurogenesis.

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We present a preparation that allows monitoring the behavior of cerebellar NSCs

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Isolated NSCs maintain their neurogenic nature in absence of niche factors

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The model enables monitoring the three postnatal cerebellar niches simultaneously

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VNUT influences the balance between quiescence and activation of cerebellar NSCs

Effects of Phosphatidylserine Source of Docosahexaenoic Acid on Cerebellar Development in Preterm Pigs

Preterm birth, a major contributor to infant mortality and morbidity, impairs development of the cerebellum, the brain region involved in cognitive processing and motor function. Previously, we showed that at term-equivalent age, preterm pigs that received formula supplemented with docosahexaenoic acid (DHA) esterified to phosphatidylserine (PS) had cerebellar weights similar to those of newborn term pigs and were heavier than control preterm pigs. However, whether PS-DHA promotes the development of specific cerebellar cell populations or enhances key developmental processes remains unknown. Here we investigated the effects of the PS-DHA on development of the cerebellum in preterm pigs delivered via caesarean section and reared for ten days on a milk replacer with either PS-DHA (experimental group) or sunflower oil (control group). Upon necropsy, key cerebellar populations were analyzed using immunohistochemistry. Consumption of PS-DHA was associated with the expansion of undifferentiated granule cell precursors and increased proliferation in the external granule cell layer (EGL). Preterm pigs that received PS-DHA also had significantly fewer apoptotic cells in the internal granule cell layer (IGL) that contains differentiated granule neurons. PS-DHA did not affect the number of differentiating granule cells in the inner EGL, thickness of the inner EGL, density of Purkinje cells, or Bergmann glial fibers, or diameter of Purkinje cells. Thus, PS-DHA may support cerebellar development in preterm subjects by enhancing proliferation of granule cells, a process specifically inhibited by preterm birth, and increasing the survival of granule cells in the IGL. These findings suggest that PS-DHA is a promising candidate for clinical studies directed at enhancing brain development.

The Non-coding Side of Medulloblastoma

Medulloblastoma (MB) is the most common pediatric brain tumor and a primary cause of cancer-related death in children. Until a few years ago, only clinical and histological features were exploited for MB pathological classification and outcome prognosis. In the past decade, the advancement of high-throughput molecular analyses that integrate genetic, epigenetic, and expression data, together with the availability of increasing wealth of patient samples, revealed the existence of four molecularly distinct MB subgroups. Their further classification into 12 subtypes not only reduced the well-characterized intertumoral heterogeneity, but also provided new opportunities for the design of targets for precision oncology. Moreover, the identification of tumorigenic and self-renewing subpopulations of cancer stem cells in MB has increased our knowledge of its biology. Despite these advancements, the origin of MB is still debated, and its molecular bases are poorly characterized. A major goal in the field is to identify the key genes that drive tumor growth and the mechanisms through which they are able to promote tumorigenesis. So far, only protein-coding genes acting as oncogenic drivers have been characterized in each MB subgroup. The contribution of the non-coding side of the genome, which produces a plethora of transcripts that control fundamental biological processes, as the cell choice between proliferation and differentiation, is still unappreciated. This review wants to fill this major gap by summarizing the recent findings on the impact of non-coding RNAs in MB initiation and progression. Furthermore, their potential role as specific MB biomarkers and novel therapeutic targets is also highlighted.

The Role of Astrocytes in the Development of the Cerebellum

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

Loss of Piccolo Function in Rats Induces Cerebellar Network Dysfunction and Pontocerebellar Hypoplasia Type 3-like Phenotypes

Piccolo, a presynaptic active zone protein, is best known for its role in the regulated assembly and function of vertebrate synapses. Genetic studies suggest a further link to several psychiatric disorders as well as Pontocerebellar Hypoplasia type 3 (PCH3). We have characterized recently generated Piccolo KO (Pclogt/gt ) rats. Analysis of rats of both sexes revealed a dramatic reduction in brain size compared with WT (Pclowt/wt ) animals, attributed to a decrease in the size of the cerebral cortical, cerebellar, and pontine regions. Analysis of the cerebellum and brainstem revealed a reduced granule cell layer and a reduction in size of pontine nuclei. Moreover, the maturation of mossy fiber afferents from pontine neurons and the expression of the α6 GABAA receptor subunit at the mossy fiber-granule cell synapse are perturbed, as well as the innervation of Purkinje cells by cerebellar climbing fibers. Ultrastructural and functional studies revealed a reduced size of mossy fiber boutons, with fewer synaptic vesicles and altered synaptic transmission. These data imply that Piccolo is required for the normal development, maturation, and function of neuronal networks formed between the brainstem and cerebellum. Consistently, behavioral studies demonstrated that adult Pclogt/gt rats display impaired motor coordination, despite adequate performance in tasks that reflect muscle strength and locomotion. Together, these data suggest that loss of Piccolo function in patients with PCH3 could be involved in many of the observed anatomical and behavioral symptoms, and that the further analysis of these animals could provide fundamental mechanistic insights into this devastating disorder.SIGNIFICANCE STATEMENT Pontocerebellar Hypoplasia Type 3 is a devastating developmental disorder associated with severe developmental delay, progressive microcephaly with brachycephaly, optic atrophy, seizures, and hypertonia with hyperreflexia. Recent genetic studies have identified non-sense mutations in the coding region of the PCLO gene, suggesting a functional link between this disorder and the presynaptic active zone. Our analysis of Piccolo KO rats supports this hypothesis, formally demonstrating that anatomical and behavioral phenotypes seen in patients with Pontocerebellar Hypoplasia Type 3 are also exhibited by these Piccolo deficient animals.

Simultaneous Requirements for Hes1 in Retinal Neurogenesis and Optic Cup-Stalk Boundary Maintenance

The bHLH transcription factor Hes1 is a key downstream effector for the Notch signaling pathway. During embryogenesis neural progenitors express low levels of Hes1 in an oscillating pattern, whereas glial brain boundary regions (e.g., isthmus) have high, sustained Hes1 levels that suppress neuronal fates. Here, we show that in the embryonic mouse retina, the optic nerve head and stalk express high Hes1, with the ONH constituting a boundary between the neural retina and glial cells that ultimately line the optic stalk. Using two Cre drivers with distinct spatiotemporal expression we conditionally inactivated Hes1, to delineate the requirements for this transcriptional repressor during retinal neurogenesis versus patterning of the optic cup and stalk. Throughout retinal neurogenesis, Hes1 maintains proliferation and blocks retinal ganglion cell formation, but surprisingly we found it also promotes cone photoreceptor genesis. In the postnatal eye, Hes1 inactivation with Rax-Cre resulted in increased bipolar neurons and a mispositioning of Müller glia. Our results indicate that Notch pathway regulation of cone genesis is more complex than previously assumed, and reveal a novel role for Hes1 in maintaining the optic cup-stalk boundary.SIGNIFICANCE STATEMENT The bHLH repressor Hes1 regulates the timing of neurogenesis, rate of progenitor cell division, gliogenesis, and maintains tissue compartment boundaries. This study expands current eye development models by showing Notch-independent roles for Hes1 in the developing optic nerve head (ONH). Defects in ONH formation result in optic nerve coloboma; our work now inserts Hes1 into the genetic hierarchy regulating optic fissure closure. Given that Hes1 acts analogously in the ONH as the brain isthmus, it prompts future investigation of the ONH as a signaling factor center, or local organizer. Embryonic development of the ONH region has been poorly studied, which is surprising given it is where the pan-ocular disease glaucoma is widely believed to inflict damage on RGC axons.

scRNA-seq in medulloblastoma shows cellular heterogeneity and lineage expansion support resistance to SHH inhibitor therapy

Targeting oncogenic pathways holds promise for brain tumor treatment, but inhibition of Sonic Hedgehog (SHH) signaling has failed in SHH-driven medulloblastoma. Cellular diversity within tumors and reduced lineage commitment can undermine targeted therapy by increasing the probability of treatment-resistant populations. Using single-cell RNA-seq and lineage tracing, we analyzed cellular diversity in medulloblastomas in transgenic, medulloblastoma-prone mice, and responses to the SHH-pathway inhibitor vismodegib. In untreated tumors, we find expected stromal cells and tumor-derived cells showing either a spectrum of neural progenitor-differentiation states or glial and stem cell markers. Vismodegib reduces the proliferative population and increases differentiation. However, specific cell types in vismodegib-treated tumors remain proliferative, showing either persistent SHH-pathway activation or stem cell characteristics. Our data show that even in tumors with a single pathway-activating mutation, diverse mechanisms drive tumor growth. This diversity confers early resistance to targeted inhibitor therapy, demonstrating the need to target multiple pathways simultaneously.

Although the hedgehog (HH) pathway is known to be deregulated in medulloblastoma, inhibitors of the pathway have shown disappointing clinical benefit. Using single-cell sequencing in a mouse model of the disease, the authors show that the response to the HH pathway inhibitor vismodegib is cell-type specific.

Aberrations in Notch-Hedgehog signalling reveal cancer stem cells harbouring conserved oncogenic properties associated with hypoxia and immunoevasion

Background

Cancer stem cells (CSCs) have innate abilities to resist even the harshest of therapies. To eradicate CSCs, parallels can be drawn from signalling modules that orchestrate pluripotency. Notch-Hedgehog hyperactivation are seen in CSCs, yet, not much is known about their conserved roles in tumour progression across cancers.

Methods

Employing a comparative approach involving 21 cancers, we uncovered clinically-relevant, pan-cancer drivers of Notch and Hedgehog. GISTIC datasets were used to evaluate copy number alterations. Receiver operating characteristic and Cox regression were employed for survival analyses.

Results

We identified a Notch-Hedgehog signature of 13 genes exhibiting high frequencies of somatic amplifications leading to transcript overexpression. The signature successfully predicted patients at risk of death in five cancers (n = 2278): glioma (P < 0.0001), clear cell renal cell (P = 0.0022), papillary renal cell (P = 0.00099), liver (P = 0.014) and stomach (P = 0.011). The signature was independent of other clinicopathological parameters and offered an additional resolution to stratify similarly-staged tumours. High-risk patients exhibited features of stemness and had more hypoxic tumours, suggesting that hypoxia may influence CSC behaviour. Notch-Hedgehog⁺ CSCs had an immune privileged phenotype associated with increased regulatory T cell function.

Conclusion

This study will set the stage for exploring adjuvant therapy targeting the Notch-Hedgehog axis to help optimise therapeutic regimes leading to successful CSC elimination.

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.

Interleukine-17 Administration Modulates Adult Hippocampal Neurogenesis and Improves Spatial Learning in Mice

Adult hippocampal neurogenesis plays an important role in health and disease. Regulating neurogenesis may be a key mechanism in the pathophysiology and treatment of several neurobehavioral disorders such as schizophrenia, depression, autism spectrum disorders and Alzheimer's disease. Cytokines are known to affect adult neurogenesis, but conflicting studies have been reported with regard to their actual role. Interleukine-17 (IL-17), a potent pro-inflammatory cytokine, has been shown to inhibit proliferation of neuroprogenitors and thus reduce hippocampal neurogenesis, while other studies suggested it can promote neurite outgrowth. In the present study we sought to explore the possible effect of a single dose administration of IL-17 on neurogenesis related behavior, i.e. spatial learning. Surprisingly, ICR mice injected with IL-17 (8 μg) had a significant slight improvement in spatial learning in the Morris water maze paradigm, without any changes in general locomotion compared with control mice. Indeed, the expression of neurogenesis related genes was down regulated following IL-17 treatment. However, we detected an upregulation in the expression of FGF-13, a gene promoting microtubule polymerization and neurite outgrowth, thus supporting neuronal maturation. We thus suggest that IL-17 has a complex role in regulating adult neurogenesis: inhibiting neuroprogenitors proliferation on one hand, while promoting maturation of already formed neuroblasts on the other hand. Our findings suggest that these roles can potentially affect neurogenesis related behavior. Its actual role in health and disease is yet to be determined.

N-acetylcysteine decreases malignant characteristics of glioblastoma cells by inhibiting Notch2 signaling

BACKGROUND

Glioblastomas multiforme (GBM) is the most devastating primary intracranial malignancy lacking effective clinical treatments. Notch2 has been established to be a prognostic marker and probably involved in GBM malignant progression. N-acetylcysteine (NAC), a precursor of intracellular glutathione (GSH), has been widely implicated in prevention and therapy of several cancers. However, the role of NAC in GBM remains unclear and the property of NAC independent of its antioxidation is largely unknown.

METHODS

The mRNA and protein levels of Notch family and other related factors were detected by RT-PCR and western blot, respectively. In addition, intracellular reactive oxygen species (ROS) was measured by flow cytometry-based DCFH-DA. Moreover, cell viability was assessed by CCK8 and cell cycle was analyzed by flow cytometry-based PI staining. The level of apoptosis was checked by flow cytometry-based Annexin V/PI. Cell migration and invasion were evaluated by wound healing and transwell invasion assays. At last, U87 Xenograft model was established to confirm whether NAC could restrain the growth of tumor.

RESULTS

Our data showed that NAC could decrease the protein level of Notch2. Meanwhile, NAC had a decreasing effect on the mRNA and protein levels of its downstream targets Hes1 and Hey1. These effects caused by NAC were independent of cellular GSH and ROS levels. The mechanism of NAC-mediated Notch2 reduction was elucidated by promoting Notch2 degradation through Itch-dependent lysosome pathway. Furthermore, NAC could prevent proliferation, migration, and invasion and might induce apoptosis in GBM cells via targeting Notch2. Significantly, NAC could suppress the growth of tumor in vivo.

CONCLUSIONS

NAC could facilitate Notch2 degradation through lysosomal pathway in an antioxidant-independent manner, thus attenuating Notch2 malignant signaling in GBM cells. The remarkable ability of NAC to inhibit cancer cell proliferation and tumor growth may implicate a novel application of NAC on GBM therapy.

The Transcriptional Regulator SnoN Promotes the Proliferation of Cerebellar Granule Neuron Precursors in the Postnatal Mouse Brain

Control of neuronal precursor cell proliferation is essential for normal brain development, and deregulation of this fundamental developmental event contributes to brain diseases. Typically, neuronal precursor cell proliferation extends over long periods of time during brain development. However, how neuronal precursor proliferation is regulated in a temporally specific manner remains to be elucidated. Here, we report that conditional KO of the transcriptional regulator SnoN in cerebellar granule neuron precursors robustly inhibits the proliferation of these cells and promotes their cell cycle exit at later stages of cerebellar development in the postnatal male and female mouse brain. In laser capture microdissection followed by RNA-Seq, designed to profile gene expression specifically in the external granule layer of the cerebellum, we find that SnoN promotes the expression of cell proliferation genes and concomitantly represses differentiation genes in granule neuron precursors in vivo Remarkably, bioinformatics analyses reveal that SnoN-regulated genes contain binding sites for the transcription factors N-myc and Pax6, which promote the proliferation and differentiation of granule neuron precursors, respectively. Accordingly, we uncover novel physical interactions of SnoN with N-myc and Pax6 in cells. In behavior analyses, conditional KO of SnoN impairs cerebellar-dependent learning in a delayed eye-blink conditioning paradigm, suggesting that SnoN-regulation of granule neuron precursor proliferation bears functional consequences at the organismal level. Our findings define a novel function and mechanism for the major transcriptional regulator SnoN in the control of granule neuron precursor proliferation in the mammalian brain.SIGNIFICANCE STATEMENT This study reports the discovery that the transcriptional regulator SnoN plays a crucial role in the proliferation of cerebellar granule neuron precursors in the postnatal mouse brain. Conditional KO of SnoN in granule neuron precursors robustly inhibits the proliferation of these cells and promotes their cycle exit specifically at later stages of cerebellar development, with biological consequences of impaired cerebellar-dependent learning. Genomics and bioinformatics analyses reveal that SnoN promotes the expression of cell proliferation genes and concomitantly represses cell differentiation genes in vivo Although SnoN has been implicated in distinct aspects of the development of postmitotic neurons, this study identifies a novel function for SnoN in neuronal precursors in the mammalian brain.

Zika virus E protein alters the properties of human fetal neural stem cells by modulating microRNA circuitry

Zika virus (ZV) infects neural stem cells (NSCs) and causes quiescence in NSCs, reducing the pool of brain cells, leading to microcephaly. Despite conscientious efforts, the molecular mechanisms for ZV-mediated effects on NSCs lack clarity. This study aimed to explore the underlying mechanisms for ZV-mediated induction of quiescence in the primary cultures of human fetal neural stem cells (fNSCs). We demonstrate that expression of ZV envelope (E) protein displays maximum quiescence in human fNSCs by accumulating cells in the G0/G1 phase of the cell cycle as compared to other non-structural proteins, viz. NS2A, NS4A and NS4B. E protein induces immature differentiation by induction of pro-neuronal genes in proliferating fNSCs, induces apoptosis in differentiating fNSCs 3 days post differentiation, and disrupts migration of cells from differentiating neurospheres. In utero electroporation of mouse brain with E protein shows drastic downregulation of proliferating cells in ventricular and subventricular zone regions. Global microRNA sequencing suggests that E protein modulates miRNA circuitry. Among differentially expressed miRNAs, we found 14 upregulated and 11 downregulated miRNAs. Mir-204-3p and mir-1273g-3p directly regulate NOTCH2 and PAX3 expression, respectively, by binding to their 3'UTR. Bioinformatic analysis using GO analysis for the targets of differentially expressed miRNAs revealed enrichment of cell cycle and developmental processes. Furthermore, WNT, CCKR, PDGF, EGF, p53, and NOTCH signaling pathways were among the top enriched pathways. Thus, our study provides evidence for the involvement of ZV E protein and novel insights into the molecular mechanism through identification of miRNA circuitry. Art work depicting the effect of Zika virus E protein on human fetal neural stem cells.

Preterm birth disrupts cerebellar development by affecting granule cell proliferation program and Bergmann glia

Preterm birth is a leading cause of long-term motor and cognitive deficits. Clinical studies suggest that some of these deficits result from disruption of cerebellar development, but the mechanisms that mediate cerebellar abnormalities in preterm infants are largely unknown. Furthermore, it remains unclear whether preterm birth and precocious exposure to the ex-utero environment directly disrupt cerebellar development or indirectly by increasing the probability of cerebellar injury, including that resulting from clinical interventions and protocols associated with the care of preterm infants. In this study, we analyzed the cerebellum of preterm pigs delivered via c-section at 91% term and raised for 10 days, until term-equivalent age. The pigs did not receive any treatments known or suspected to affect cerebellar development and had no evidence of brain damage. Term pigs sacrificed at birth were used as controls. Immunohistochemical analysis revealed that preterm birth did not affect either size or numbers of Purkinje cells or molecular layer interneurons at term-equivalent age. The number of granule cell precursors and Bergmann glial fibers, however, were reduced in preterm pigs. Preterm pigs had reduced proliferation but not differentiation of granule cells. qRT-PCR analysis of laser capture microdissected external granule cell layer showed that preterm pigs had a reduced expression of Ccnd1 (Cyclin D1), Ccnb1 (Cyclin B1), granule cell master regulatory transcription factor Atoh1, and signaling molecule Jag1. In vitro rescue experiments identified Jag1 as a central granule cell gene affected by preterm birth. Thus, preterm birth and precocious exposure to the ex-utero environment disrupt cerebellum by modulating expression of key cerebellar developmental genes, predominantly affecting development of granule precursors and Bergmann glia.

METTL3-mediated m6A modification is required for cerebellar development

N⁶-methyladenosine (m⁶A) RNA methylation is the most abundant modification on mRNAs and plays important roles in various biological processes. The formation of m⁶A is catalyzed by a methyltransferase complex including methyltransferase-like 3 (METTL3) as a key factor. However, the in vivo functions of METTL3 and m⁶A modification in mammalian development remain unclear. Here, we show that specific inactivation of Mettl3 in mouse nervous system causes severe developmental defects in the brain. Mettl3 conditional knockout (cKO) mice manifest cerebellar hypoplasia caused by drastically enhanced apoptosis of newborn cerebellar granule cells (CGCs) in the external granular layer (EGL). METTL3 depletion–induced loss of m⁶A modification causes extended RNA half-lives and aberrant splicing events, consequently leading to dysregulation of transcriptome-wide gene expression and premature CGC death. Our findings reveal a critical role of METTL3-mediated m⁶A in regulating the development of mammalian cerebellum.

N⁶-methyladenosine (m⁶A) is an abundant modification in mRNA molecules and regulates mRNA metabolism and various biological processes, such as cell fate control, early embryonic development, sex determination, and diseases like diabetes and obesity. Adenosine methylation is regulated by a large methyltransferase complex and by demethylases, as well as by other binding proteins. METTL3 is one of the core subunits of the methyltransferase complex catalyzing m⁶A formation. However, the role of METTL3-mediated m⁶A in mammalian brain development remains unclear mainly because of the lack of specific spatiotemporal knockout animal models, as conventional METTL3 knockout in mice leads to early embryonic death. In this study, we specifically inactivated METTL3 in the developing mouse brain. We detected a drastic depletion of m⁶A accompanied by severe developmental defects in the cerebellum of these mice. Further analysis established that METTL3-mediated m⁶A participates in cerebellar development by controlling mRNA stability of genes related to cerebellar development and apoptosis and by regulating alternative splicing of pre-mRNAs of synapse-associated genes.

VRTN is Required for the Development of Thoracic Vertebrae in Mammals

Vertnin (VRTN) variants are associated with thoracic vertebral number (TVN) in pigs. However, the biological function of VRTN remains poorly understood. Here we first conducted a range of experiments to demonstrate that VRTN is a responsible gene for TVN and two causative variants in the regulatory region of VRTN additively regulate TVN. Then, we show that VRTN is a novel DNA-binding transcription factor as it localizes exclusively in the nucleus, binds to DNA on a genome-wide scale and regulates the transcription of a set of genes that harbor VRTN binding motifs. Next, we illustrate that VRTN is essential for the development of thoracic vertebrae. Vrtn-null embryos display somitogenesis defect with the failure of axial rotation and fewer somites at the thoracic somite stage. Half of Vrtn heterozygous mice show abnormal spinal development with fewer thoracic vertebrae and ribs than their wild-type littermates. Lastly, we reveal that VRTN could modulate somite segmentation via the Notch signaling pathway. The findings advance our understanding of the mechanisms underlying the development of thoracic vertebrate in mammals, and VRTN causative variants provide a robust tool to improve pork production by selecting the alleles increasing the number of thoracic vertebrae and ribs.

Linking neuronal lineage and wiring specificity

Brain function requires precise neural circuit assembly during development. Establishing a functional circuit involves multiple coordinated steps ranging from neural cell fate specification to proper matching between pre- and post-synaptic partners. How neuronal lineage and birth timing influence wiring specificity remains an open question. Recent findings suggest that the relationships between lineage, birth timing, and wiring specificity vary in different neuronal circuits. In this review, we summarize our current understanding of the cellular, molecular, and developmental mechanisms linking neuronal lineage and birth timing to wiring specificity in a few specific systems in Drosophila and mice, and review different methods employed to explore these mechanisms.

Embryology

With the growing recognition of the extent and prevalence of human cerebellar disorders, an understanding of developmental programs that build the mature cerebellum is necessary. In this chapter we present an overview of the basic epochs and key molecular regulators of the developmental programs of cerebellar development. These include early patterning of the cerebellar territory, the genesis of cerebellar cells from multiple spatially distinct germinal zones, and the extensive migration and coordinated cellular rearrangements that result in the formation of the exquisitely foliated and laminated mature cerebellum. This knowledge base is founded on extensive analysis of animal models, particularly mice, due in large part to the ease of genetic manipulation of this important model organism. Since cerebellar structure and function are largely conserved across species, mouse cerebellar development is highly relevant to humans and has led to important insights into the developmental pathogenesis of human cerebellar disorders. Human fetal cerebellar development remains largely undescribed; however, several human-specific developmental features are known which are relevant to human disease and underline the importance of ongoing human fetal research.

Maml1 acts cooperatively with Gli proteins to regulate sonic hedgehog signaling pathway

Sonic hedgehog (Shh) signaling is essential for proliferation of cerebellar granule cell progenitors (GCPs) and its misregulation is linked to various disorders, including cerebellar cancer medulloblastoma. The effects of Shh pathway are mediated by the Gli family of transcription factors, which controls the expression of a number of target genes, including Gli1. Here, we identify Mastermind-like 1 (Maml1) as a novel regulator of the Shh signaling since it interacts with Gli proteins, working as a potent transcriptional coactivator. Notably, Maml1 silencing results in a significant reduction of Gli target genes expression, with a negative impact on cell growth of NIH3T3 and Patched1^−/− mouse embryonic fibroblasts (MEFs), bearing a constitutively active Shh signaling. Remarkably, Shh pathway activity results severely compromised both in MEFs and GCPs deriving from Maml1^−/− mice with an impairment of GCPs proliferation and cerebellum development. Therefore Maml1^−/− phenotype mimics aspects of Shh pathway deficiency, suggesting an intrinsic requirement for Maml1 in cerebellum development. The present study shows a new role for Maml1 as a component of Shh signaling, which plays a crucial role in both development and tumorigenesis.

Neonatal Hyperoxia Perturbs Neuronal Development in the Cerebellum

Impaired postnatal brain development of preterm infants often results in neurological deficits. Besides pathologies of the forebrain, maldeveolopment of the cerebellum is increasingly recognized to contribute to psychomotor impairments of many former preterm infants. However, causes are poorly defined. We used a hyperoxia model to define neonatal damage in cerebellar granule cell precursors (GCPs) and in Purkinje cells (PCs) known to be essential for interaction with GCPs during development. We exposed newborn rats to 24 h 80% O₂ from age P6 to P7 to identify postnatal and long-term damage in cerebellar GCPs at age P7 after hyperoxia and also after recovery in room air thereafter until P11 and P30. We determined proliferation and apoptosis of GCPs and immature neurons by immunohistochemistry, quantified neuronal damage by qPCR and Western blots for neuronal markers, and measured dendrite outgrowth of PCs by CALB1 immunostainings and by Sholl analysis of Golgi stainings. After hyperoxia, proliferation of PAX6+ GCPs was decreased at P7, while DCX + CASP3+ cells were increased at P11. Neuronal markers Pax6, Tbr2, and Prox1 were downregulated at P11 and P30. Neuronal damage was confirmed by reduced NeuN protein expression at P30. Sonic hedgehog (SHH) was significantly decreased at P7 and P11 after hyperoxia and coincided with lower CyclinD2 and Hes1 expression at P7. The granule cell injury was accompanied by hampered PC maturation with delayed dendrite formation and impaired branching. Neonatal injury induced by hyperoxia inhibits PC functioning and impairs granule cell development. As a conclusion, maldevelopment of the cerebellar neurons found in preterm infants could be caused by postnatal oxygen toxicity.

Response of antioxidant enzymes to cadmium-induced cytotoxicity in rat cerebellar granule neurons

Cadmium (Cd) accumulates in the brain and can damage neurons via complex processes involving oxidative stress induction. In this study we used a homogenous population of neurons which are cerebellar granule neurons (CGNs) to investigate damage induced by Cd and its effects on antioxidant enzyme activity. The exposure of CGNs to increasing concentrations of Cd (2.5 μM-100 μM) during 24 h, 48 h, or 72 h led to the induction of neuronal death in a dose- and exposure time-dependent manner. The necrotic and/or apoptotic pathway involved in the cell death trigged by Cd seems to depend on the concentration of Cd and the exposure time. In addition to its cell damage, Cd was shown to affect the activity of superoxide dismutase (SOD) and catalase (CAT) depending on the concentration of Cd and the exposure time. We also found that the exposure to Cd induces a bigger change in SOD activity than in CAT activity. Taken together, our findings explain, in part, the mechanism of Cd toxicity in a specific type of neuron which can provide information related to neurological pathologies ascribed to Cd toxicity.

Wnt5a is a crucial regulator of neurogenesis during cerebellum development

The role of Wnt5a has been extensively explored in various aspects of development but its role in cerebellar development remains elusive. Here, for the first time we unravel the expression pattern and functional significance of Wnt5a in cerebellar development using Wnt5a^−/− and Nestin-Cre mediated conditional knockout mouse models. We demonstrate that loss of Wnt5a results in cerebellar hypoplasia and depletion of GABAergic and glutamatergic neurons. Besides, Purkinje cells of the mutants displayed stunted, poorly branched dendritic arbors. Furthermore, we show that the overall reduction is due to decreased radial glial and granule neuron progenitor cell proliferation. At molecular level we provide evidence for non-canonical mode of action of Wnt5a and its regulation over genes associated with progenitor proliferation. Altogether our findings imply that Wnt5a signaling is a crucial regulator of cerebellar development and would aid in better understanding of cerebellar disease pathogenesis caused due to deregulation of Wnt signaling.

MafB is required for development of the hindbrain choroid plexus

The choroid plexus (ChP) is a non-neural epithelial tissue that produces cerebrospinal fluid (CSF). The ChP differentiates from the roof plate, a dorsal midline structure of the neural tube. However, molecular mechanisms underlying ChP development are poorly understood compared to neural development. MafB is a bZip transcription factor that is known to be expressed in the roof plate. Here we investigated the role of MafB in embryonic development of the hindbrain ChP (hChP) using Mafb-deficient mice. Immunohistochemical analyses revealed that MafB is expressed in the roof plate and early hChP epithelial cells but its expression disappears at a later embryonic stage. We also found that the Mafb-deficient hChP exhibits delayed differentiation and results in hypoplasia compared to the wild-type hChP. Furthermore, the Mafb-deficient hChP exhibits increased apoptotic cell death and decreased proliferating cells at E12.5, an early stage of hChP development. Collectively, our findings reveal that MafB play an important role in promoting hChP development during embryogenesis.

Consensus Paper: Cerebellar Development

The development of the mammalian cerebellum is orchestrated by both cell-autonomous programs and inductive environmental influences. Here, we describe the main processes of cerebellar ontogenesis, highlighting the neurogenic strategies used by developing progenitors, the genetic programs involved in cell fate specification, the progressive changes of structural organization, and some of the better-known abnormalities associated with developmental disorders of the cerebellum.

Cell-type-specific expression of NFIX in the developing and adult cerebellum

Transcription factors from the nuclear factor one (NFI) family have been shown to play a central role in regulating neural progenitor cell differentiation within the embryonic and post-natal brain. NFIA and NFIB, for instance, promote the differentiation and functional maturation of granule neurons within the cerebellum. Mice lacking Nfix exhibit delays in the development of neuronal and glial lineages within the cerebellum, but the cell-type-specific expression of this transcription factor remains undefined. Here, we examined the expression of NFIX, together with various cell-type-specific markers, within the developing and adult cerebellum using both chromogenic immunohistochemistry and co-immunofluorescence labelling and confocal microscopy. In embryos, NFIX was expressed by progenitor cells within the rhombic lip and ventricular zone. After birth, progenitor cells within the external granule layer, as well as migrating and mature granule neurons, expressed NFIX. Within the adult cerebellum, NFIX displayed a broad expression profile, and was evident within granule cells, Bergmann glia, and interneurons, but not within Purkinje neurons. Furthermore, transcriptomic profiling of cerebellar granule neuron progenitor cells showed that multiple splice variants of Nfix are expressed within this germinal zone of the post-natal brain. Collectively, these data suggest that NFIX plays a role in regulating progenitor cell biology within the embryonic and post-natal cerebellum, as well as an ongoing role within multiple neuronal and glial populations within the adult cerebellum.

Tumor cells with neuronal intermediate progenitor features define a subgroup of 1p/19q co-deleted anaplastic gliomas

The integrated diagnosis of anaplastic oligodendroglioma, IDH mutant and 1p/19q co-deleted, grade III (O3^id ) is a histomolecular entity that WHO 2016 classification distinguished from other diffuse gliomas by specific molecular alterations. In contrast, its cell portrait is less well known. The present study is focused on intertumor and intratumor, cell lineage-oriented, heterogeneity in O3^id . Based on pathological, transcriptomic and immunophenotypic studies, a novel subgroup of newly diagnosed O3^id overexpressing neuronal intermediate progenitor (NIP) genes was identified. This NIP overexpression pattern in O3^id is associated with: (i) morphological and immunohistochemical similarities with embryonic subventricular zone, (ii) proliferating tumor cell subpopulation with NIP features including expression of INSM1 and no expression of SOX9, (iii) mutations in critical genes involved in NIP biology and, (iv) increased tumor necrosis. Interestingly, NIP tumor cell subpopulation increases in O3^id recurrence compared with paired newly diagnosed tumors. Our results, validated in an independent cohort, emphasize intertumor and intratumor heterogeneity in O3^id and identified a tumor cell subpopulation exhibiting NIP characteristics that is potentially critical in oncogenesis of O3^id . A better understanding of spatial and temporal intratumor cell heterogeneity in O3^id will open new therapeutic avenues overcoming resistance to current antitumor treatments.

Aquaporins: Multiple Roles in the Central Nervous System

Aquaporins (AQPs) represent a diverse family of membrane proteins found in prokaryotes and eukaryotes. The primary aquaporins expressed in the mammalian brain are AQP1, which is densely packed in choroid plexus cells lining the ventricles, and AQP4, which is abundant in astrocytes and concentrated especially in the end-feet structures that surround capillaries throughout the brain and are present in glia limitans structures, notably in osmosensory areas such the supraoptic nucleus. Water movement in brain tissues is carefully regulated from the micro- to macroscopic levels, with aquaporins serving key roles as multifunctional elements of complex signaling assemblies. Intriguing possibilities suggest links for AQP1 in Alzheimer's disease, AQP4 as a target for therapy in brain edema, and a possible contribution of AQP9 in Parkinson's disease. For all the aquaporins, new contributions to physiological functions are likely to continue to be discovered with ongoing work in this rapidly expanding field of research. NEUROSCIENTIST 13(5):470—485, 2007.

Zeb1 controls neuron differentiation and germinal zone exit by a mesenchymal-epithelial-like transition

In the developing mammalian brain, differentiating neurons mature morphologically via neuronal polarity programs. Despite discovery of polarity pathways acting concurrently with differentiation, it's unclear how neurons traverse complex polarity transitions or how neuronal progenitors delay polarization during development. We report that zinc finger and homeobox transcription factor-1 (Zeb1), a master regulator of epithelial polarity, controls neuronal differentiation by transcriptionally repressing polarity genes in neuronal progenitors. Necessity-sufficiency testing and functional target screening in cerebellar granule neuron progenitors (GNPs) reveal that Zeb1 inhibits polarization and retains progenitors in their germinal zone (GZ). Zeb1 expression is elevated in the Sonic Hedgehog (SHH) medulloblastoma subgroup originating from GNPs with persistent SHH activation. Restored polarity signaling promotes differentiation and rescues GZ exit, suggesting a model for future differentiative therapies. These results reveal unexpected parallels between neuronal differentiation and mesenchymal-to-epithelial transition and suggest that active polarity inhibition contributes to altered GZ exit in pediatric brain cancers.

DOI:http://dx.doi.org/10.7554/eLife.12717.001

During the formation of the brain, developing neurons are faced with a logistical problem. After newborn neurons form they must change in shape and move to their final location in the brain. Despite much speculation, little is known about these processes.

Neurons mature via the activity of several pathways that control the activity, or expression, of the neuron’s genes. One way of controlling such gene expression is through proteins called transcription factors. At the same time, the developing neurons go through a process called polarization, where different regions of the cell develop different characteristics. However, it was not known how the maturation and polarization processes are linked, or how the developing neurons actively regulate polarization.

By studying the developing mouse brain, Singh et al. found that a transcription factor called Zeb1 keeps neurons in a immature state, stopping them from becoming polarized. Further investigation revealed that Zeb1 does this by preventing the production of a group of proteins that helps to polarize the cells.

The most common type of malignant brain tumour in children is called a medulloblastoma. Singh et al. analyzed the genes expressed in mice that have a type of medulloblastoma that results from the constant activity of a gene called Sonic Hedgehog in developing neurons. This revealed that these tumour cells contain abnormally high levels of Zeb1, and so do not take on a polarized form. However, artificially restoring other factors that encourage the cells to polarize caused the neurons to mature normally. Further investigation is now needed to find out whether the activity of the Sonic Hedgehog gene regulates Zeb1 activity, and to discover whether inhibiting Zeb1 could prevent brain tumours from developing.

DOI:http://dx.doi.org/10.7554/eLife.12717.002

Bioinformatic analyses reveal a distinct Notch activation induced by STAT3 phosphorylation in the mesenchymal subtype of glioblastoma

OBJECTIVE Glioblastoma (GBM) is the most common and lethal type of malignant glioma. The Cancer Genome Atlas divides the gene expression-based classification of GBM into classical, mesenchymal, neural, and proneural subtypes, which is important for understanding GBM etiology and for designing effective personalized therapy. Signal transducer and activator of transcription 3 (STAT3), a critical transcriptional activator in tumorigenesis, is persistently phosphorylated and associated with an unfavorable prognosis in GBM. Although a set of specific targets has been identified, there have been no systematic analyses of STAT3 signaling based on GBM subtype. METHODS This study compared STAT3-associated messenger RNA, protein, and microRNA expression profiles across different subtypes of GBM. RESULTS The analyses revealed a prominent role for STAT3 in the mesenchymal but not in other GBM subtypes, which can be reliably used to classify patients with mesenchymal GBM into 2 groups according to phosphorylated STAT3 expression level. Differentially expressed genes suggest an association between Notch and STAT3 signaling in the mesenchymal subtype. Their association was validated in the U87 cell, a malignant glioma cell line annotated as mesenchymal subtype. Specific associated proteins and microRNAs further profile the STAT3 signaling among GBM subtypes. CONCLUSIONS These findings suggest a prominent role for STAT3 signaling in mesenchymal GBM and highlight the importance of identifying signaling pathways that contribute to specific cancer subtypes.

Drosophila Brat and Human Ortholog TRIM3 Maintain Stem Cell Equilibrium and Suppress Brain Tumorigenesis by Attenuating Notch Nuclear Transport

Cancer stem cells exert enormous influence on neoplastic behavior, in part by governing asymmetric cell division and the balance between self-renewal and multipotent differentiation. Growth is favored by deregulated stem cell division, which enhances the self-renewing population and diminishes the differentiation program. Mutation of a single gene in Drosophila, Brain Tumor (Brat), leads to disrupted asymmetric cell division resulting in dramatic neoplastic proliferation of neuroblasts and massive larval brain overgrowth. To uncover the mechanisms relevant to deregulated cell division in human glioma stem cells, we first developed a novel adult Drosophila brain tumor model using brat-RNAi driven by the neuroblast-specific promoter inscuteable Suppressing Brat in this population led to the accumulation of actively proliferating neuroblasts and a lethal brain tumor phenotype. brat-RNAi caused upregulation of Notch signaling, a node critical for self-renewal, by increasing protein expression and enhancing nuclear transport of Notch intracellular domain (NICD). In human glioblastoma, we demonstrated that the human ortholog of Drosophila Brat, tripartite motif-containing protein 3 (TRIM3), similarly suppressed NOTCH1 signaling and markedly attenuated the stem cell component. We also found that TRIM3 suppressed nuclear transport of active NOTCH1 (NICD) in glioblastoma and demonstrated that these effects are mediated by direct binding of TRIM3 to the Importin complex. Together, our results support a novel role for Brat/TRIM3 in maintaining stem cell equilibrium and suppressing tumor growth by regulating NICD nuclear transport. Cancer Res; 76(8); 2443-52. ©2016 AACR.