Genes involved in cerebellar cell specification and differentiation

Syndecan-3 regulates the time of transition from cell cycle exit to initial differentiation stage in mouse cerebellar granule cell precursors

To analyze the role of syndecan-3 (SDC3), a heparan sulfate proteoglycan, in cerebellum development, we examined the effect of SDC3 on the transition from cell cycle exit to the initial differentiation stage of cerebellar granule cell precursors (CGCPs). First, we examined SDC3 localization in the developing cerebellum. SDC3 was mainly localized to the inner external granule layer where the transition from the cell cycle exit to the initial differentiation of CGCPs occurs. To examine how SDC3 regulates the cell cycle exit of CGCPs, we performed SDC3-knockdown (SDC3-KD) and -overexpression (Myc-SDC3) assays using primary CGCPs. SDC3-KD significantly increased the ratio of p27^Kip1+ cells to total cells at day 3 in vitro (DIV3) and 4, but Myc-SDC3 reduced that at DIV3. Regarding the cell cycle exit efficiency using 24 h-labelled bromodeoxyuridine (BrdU) and a marker of cell cycling, Ki67, SDC3-KD significantly increased cell cycle exit efficiency (Ki67^-; BrdU⁺ cells/BrdU⁺ cells) in primary CGCP at DIV4 and 5, but Myc-SDC3 reduced that at DIV4 and 5. However, SDC3-KD and Myc-SDC3 did not affect the efficiency of the final differentiation from CGCPs to granule cells at DIV3-5. Furthermore, the ratio of CGCPs in the cell cycle exiting stage to total cells, identified by initial differentiation markers TAG1 and Ki67 (TAG1⁺; Ki67⁺ cells), was considerably decreased by SDC3-KD at DIV4, but increased by Myc-SDC3 at DIV4 and 5. Altogether, these results indicate that SDC3 regulates the timing of the transition from the cell cycle exit stage to the initial differentiation stage of CGCP.

The long noncoding RNA Synage regulates synapse stability and neuronal function in the cerebellum

The brain is known to express many long noncoding RNAs (lncRNAs); however, whether and how these lncRNAs function in modulating synaptic stability remains unclear. Here, we report a cerebellum highly expressed lncRNA, Synage, regulating synaptic stability via at least two mechanisms. One is through the function of Synage as a sponge for the microRNA miR-325-3p, to regulate expression of the known cerebellar synapse organizer Cbln1. The other function is to serve as a scaffold for organizing the assembly of the LRP1-HSP90AA1-PSD-95 complex in PF-PC synapses. Although somewhat divergent in its mature mRNA sequence, the locus encoding Synage is positioned adjacent to the Cbln1 loci in mouse, rhesus macaque, and human, and Synage is highly expressed in the cerebella of all three species. Synage deletion causes a full-spectrum cerebellar ablation phenotype that proceeds from cerebellar atrophy, through neuron loss, on to synapse density reduction, synaptic vesicle loss, and finally to a reduction in synaptic activity during cerebellar development; these deficits are accompanied by motor dysfunction in adult mice, which can be rescued by AAV-mediated Synage overexpression from birth. Thus, our study demonstrates roles for the lncRNA Synage in regulating synaptic stability and function during cerebellar development.

Single-cell spatial transcriptomic analysis reveals common and divergent features of developing postnatal granule cerebellar cells and medulloblastoma

BACKGROUND

Cerebellar neurogenesis involves the generation of large numbers of cerebellar granule neurons (GNs) throughout development of the cerebellum, a process that involves tight regulation of proliferation and differentiation of granule neuron progenitors (GNPs). A number of transcriptional regulators, including Math1, and the signaling molecules Wnt and Shh have been shown to have important roles in GNP proliferation and differentiation, and deregulation of granule cell development has been reported to be associated with the pathogenesis of medulloblastoma. While the progenitor/differentiation states of cerebellar granule cells have been broadly investigated, a more detailed association between developmental differentiation programs and spatial gene expression patterns, and how these lead to differential generation of distinct types of medulloblastoma remains poorly understood. Here, we provide a comparative single-cell spatial transcriptomics analysis to better understand the similarities and differences between developing granule and medulloblastoma cells.

RESULTS

To acquire an enhanced understanding of the precise cellular states of developing cerebellar granule cells, we performed single-cell RNA sequencing of 24,919 murine cerebellar cells from granule neuron-specific reporter mice (Math1-GFP; Dcx-DsRed mice). Our single-cell analysis revealed that there are four major states of developing cerebellar granule cells, including two subsets of granule progenitors and two subsets of differentiating/differentiated granule neurons. Further spatial transcriptomics technology enabled visualization of their spatial locations in cerebellum. In addition, we performed single-cell RNA sequencing of 18,372 cells from Patched+/- mutant mice and found that the transformed granule cells in medulloblastoma closely resembled developing granule neurons of varying differentiation states. However, transformed granule neuron progenitors in medulloblastoma exhibit noticeably less tendency to differentiate compared with cells in normal development.

CONCLUSION

In sum, our study revealed the cellular and spatial organization of the detailed states of cerebellar granule cells and provided direct evidence for the similarities and discrepancies between normal cerebellar development and tumorigenesis.

Vitronectin regulates the axon specification of mouse cerebellar granule cell precursors via αvβ5 integrin in the differentiation stage

Vitronectin, an extracellular matrix protein, controls the differentiation of cerebellar granule cell precursors (CGCPs) via αvβ5 integrin, particularly in the initial stage of differentiation to granule cells. In this study, we determined whether vitronectin regulates axon specification in this initial differentiation stage of CGCPs. First, we analyzed whether vitronectin deficiency, β5 integrin knockdown (KD), and β5 integrin overexpression affect axon specification of primary cultured CGCPs. Vitronectin deficiency and β5 integrin KD inhibited axon formation, while vitronectin administrated- and β5 integrin overexpressed-neurons formed multiple axons. Moreover, KD of β5 integrin suppressed vitronectin-induced multiple axon formation. These findings indicate that vitronectin contributes to regulating axon specification via αvβ5 integrin in CGCPs. Next, we determined the signaling pathway involved in regulating vitronectin-induced axon specification. Wortmannin, an inhibitor of phosphatidylinositol 3-kinase (PI3K), inhibited vitronectin-induced multiple axon specification, and lithium chloride, an inhibitor of glyocogen synthase kinase 3 beta (GSK3β), attenuated the inhibitory effect of vitronectin-KO and β5 integrin KD on the specification of CGCPs. In addition, vitronectin induced the phosphorylation of protein kinase B (Akt) and GSK3β in neuroblastoma Neuro2a cells. Taken together, our results indicate that vitronectin plays an important factor in axon formation process in CGCPs via a β5 integrin/PI3K/GSK3β pathway.

Heterochronic Developmental Shifts Underlying Squamate Cerebellar Diversity Unveil the Key Features of Amniote Cerebellogenesis

Despite a remarkable conservation of architecture and function, the cerebellum of vertebrates shows extensive variation in morphology, size, and foliation pattern. These features make this brain subdivision a powerful model to investigate the evolutionary developmental mechanisms underlying neuroanatomical complexity both within and between anamniote and amniote species. Here, we fill a major evolutionary gap by characterizing the developing cerebellum in two non-avian reptile species-bearded dragon lizard and African house snake-representative of extreme cerebellar morphologies and neuronal arrangement patterns found in squamates. Our data suggest that developmental strategies regarded as exclusive hallmark of birds and mammals, including transit amplification in an external granule layer (EGL) and Sonic hedgehog expression by underlying Purkinje cells (PCs), contribute to squamate cerebellogenesis independently from foliation pattern. Furthermore, direct comparison of our models suggests the key importance of spatiotemporal patterning and dynamic interaction between granule cells and PCs in defining cortical organization. Especially, the observed heterochronic shifts in early cerebellogenesis events, including upper rhombic lip progenitor activity and EGL maintenance, are strongly expected to affect the dynamics of molecular interaction between neuronal cell types in snakes. Altogether, these findings help clarifying some of the morphogenetic and molecular underpinnings of amniote cerebellar corticogenesis, but also suggest new potential molecular mechanisms underlying cerebellar complexity in squamates. Furthermore, squamate models analyzed here are revealed as key animal models to further understand mechanisms of brain organization.

PR domaincontaining protein 12 (prdm12) is a downstream target of the transcription factor zic1 during cellular differentiation in the central nervous system: PR domain containing protein is the right form

Transcription factor zic1 is an important regulator of neural plate patterning, formation of neural crest and cerebellar development, where its main function is neuronal cell differentiation. Among the genes identified, PR domain-containing 12 (prdm12) is a member of the prdm family and is expressed in the placode domain in the neurula stage. prdm12 is distinctly expressed in the dorsal part of the midbrain, trigeminal ganglion, and the motor neuron in the spinal cord. prdm12 knockdown results in the ventralization of the neural tube. zic1 knockdown results in the reduction of prdm12 expression in the midbrain, motor neuron and trigeminal ganglion, and overexpression of zic1 results in the expansion of prdm12 expression in the midbrain. zic1-activated wnt signaling is also a regulator of prdm12 expression in the midbrain. We propose that prdm12 is the downstream of zic1 and a novel player in the gene regulatory network controlling brain cell differentiation, along with some ganglions in Xenopus.

Status Epilepticus Increases Cell Proliferation and Neurogenesis in the Developing Rat Cerebellum

Status epilepticus (SE) promotes neuronal proliferation and differentiation in the adult and developing rodent hippocampus. However, the effect of SE on other neurogenic brain regions such as the cerebellum has been less explored. To determine whether SE induced by pentylentetrazole (PTZ-SE) and lithium-pilocarpine (Li-Pilo-SE) increases cell proliferation and neurogenesis in the developing rat cerebellum. SE was induced in 14-day-old (P14) Wistar rat pups (both sexes). One hour after SE and the following day rats were injected intraperitoneally with 5-bromo-2'-deoxyuridine (BrdU, 50 mg/kg). Seven days after SE, immunohistochemistry was performed to detect BrdU-positive (BrdU+) cells or BrdU/NeuN+ cells in the cerebellar vermis. SE induced by PTZ or Li-Pilo statistically significant increased the number of cerebellar BrdU+ cells when compared with the control group (58% and 40%, respectively); maximal cell proliferation occurred in lobules II, III, VIb, VIc, VIII, IXa, and IXb of PTZ-SE group and II, V, VIc, VII, and X of Li-Pilo-SE group. An increased number of BrdU/NeuN+ cells was detected in lobules V (17 ± 1.9), VIc (25.8 ± 2.7), and VII (26.2 ± 3.4) after Li-Pilo-SE compared to their control group (9.8 ± 1.7, 12.8 ± 2.8, and 11 ± 1.7, respectively), while the number of BrdU/NeuN+ cells remained the same after PTZ-induced SE or control conditions. SE induced in the developing rat by different experimental models increases cell proliferation in the granular layer of the cerebellar vermis, but only SE of limbic seizures increases neurogenesis in specific cerebellar lobes.

Upregulation of the chromatin remodeler HELLS is mediated by YAP1 in Sonic Hedgehog Medulloblastoma

Medulloblastoma is a malignant pediatric tumor that arises from neural progenitors in the cerebellum. Despite a five-year survival rate of ~70%, nearly all patients incur adverse side effects from current treatment strategies that drastically impact quality of life. Roughly one-third of medulloblastoma are driven by aberrant activation of the Sonic Hedgehog (SHH) signaling pathway. However, the scarcity of genetic mutations in medulloblastoma has led to investigation of other mechanisms contributing to cancer pathogenicity including epigenetic regulation of gene expression. Here, we show that Helicase, Lymphoid Specific (HELLS), a chromatin remodeler with epigenetic functions including DNA methylation and histone modification, is induced by Sonic Hedgehog (SHH) in SHH-dependent cerebellar progenitor cells and the developing murine cerebella. HELLS is also up-regulated in mouse and human SHH medulloblastoma. Others have shown that HELLS activity generally results in a repressive chromatin state. Our results demonstrate that increased expression of HELLS in our experimental systems is regulated by the oncogenic transcriptional regulator YAP1 downstream of Smoothened, the positive transducer of SHH signaling. Elucidation of HELLS as one of the downstream effectors of the SHH pathway may lead to novel targets for precision therapeutics with the promise of better outcomes for SHH medulloblastoma patients.

Cend1, a Story with Many Tales: From Regulation of Cell Cycle Progression/Exit of Neural Stem Cells to Brain Structure and Function

Neural stem/precursor cells (NPCs) generate the large variety of neuronal phenotypes comprising the adult brain. The high diversity and complexity of this organ have its origin in embryonic life, during which NPCs undergo symmetric and asymmetric divisions and then exit the cell cycle and differentiate to acquire neuronal identities. During these processes, coordinated regulation of cell cycle progression/exit and differentiation is essential for generation of the appropriate number of neurons and formation of the correct structural and functional neuronal circuits in the adult brain. Cend1 is a neuronal lineage-specific modulator involved in synchronization of cell cycle exit and differentiation of neuronal precursors. It is expressed all along the neuronal lineage, from neural stem/progenitor cells to mature neurons, and is associated with the dynamics of neuron-generating divisions. Functional studies showed that Cend1 has a critical role during neurogenesis in promoting cell cycle exit and neuronal differentiation. Mechanistically, Cend1 acts via the p53-dependent/Cyclin D1/pRb signaling pathway as well as via a p53-independent route involving a tripartite interaction with RanBPM and Dyrk1B. Upon Cend1 function, Notch1 signaling is suppressed and proneural genes such as Mash1 and Neurogenins 1/2 are induced. Due to its neurogenic activity, Cend1 is a promising candidate therapeutic gene for brain repair, while the Cend1 minimal promoter is a valuable tool for neuron-specific gene delivery in the CNS. Mice with Cend1 genetic ablation display increased NPC proliferation, decreased migration, and higher levels of apoptosis during development. As a result, they show in the adult brain deficits in a range of motor and nonmotor behaviors arising from irregularities in cerebellar cortex lamination and impaired Purkinje cell differentiation as well as a paucity in GABAergic interneurons of the cerebral cortex, hippocampus, and amygdala. Taken together, these studies highlight the necessity for Cend1 expression in the formation of a structurally and functionally normal brain.

Roles of Cdc42 and Rac in Bergmann glia during cerebellar corticogenesis

Bergmann glia (BG) are important in the inward type of radial migration of cerebellar granule neurons (CGNs). However, details regarding the functions of Cdc42 and Rac in BG for radial migration of CGN are unknown. To examine the roles of Cdc42 and Rac in BG during cerebellar corticogenesis, mice with a single deletion of Cdc42 or Rac1 and those with double deletions of Cdc42 and Rac1 under control of the glial fibrillary acidic protein (GFAP) promoter: GFAP-Cre;Cdc42^flox/flox (Cdc42-KO), GFAP-Cre;Rac1^flox/flox (Rac1-KO), and GFAP-Cre; Cdc42^flox/flox;Rac1^flox/flox (Cdc42/Rac1-DKO) mice, were generated. Both Cdc42-KO and Rac1-KO mice, but more obviously Cdc42-KO mice, had disturbed alignment of BG in the Purkinje cell layer (PCL). We found that Cdc42-KO, but not Rac1-KO, induced impaired radial migration of CGNs in the late phase of radial migration, leading to retention of CGNs in the lower half of the molecular layer (ML). Cdc42-KO, but not Rac1-KO, mice also showed aberrantly aligned Purkinje cells (PCs). These phenotypes were exacerbated in Cdc42/Rac1-DKO mice. Alignment of BG radial fibers in the ML and BG endfeet at the pial surface of the cerebellum evaluated by GFAP staining was disturbed and weak in Cdc42/Rac1-DKO mice, respectively. Our data indicate that Cdc42 and Rac, but predominantly Cdc42, in BG play important roles during the late phase of radial migration of CGNs. We also report here that Cdc42 is involved in gliophilic migration of CGNs, in contrast to Rac, which is more closely connected to regulating neurophilic migration.

Obstacles to Brain Tumor Therapy: Key ABC Transporters

The delivery of cancer chemotherapy to treat brain tumors remains a challenge, in part, because of the inherent biological barrier, the blood-brain barrier. While its presence and role as a protector of the normal brain parenchyma has been acknowledged for decades, it is only recently that the important transporter components, expressed in the tightly knit capillary endothelial cells, have been deciphered. These transporters are ATP-binding cassette (ABC) transporters and, so far, the major clinically important ones that functionally contribute to the blood-brain barrier are ABCG2 and ABCB1. A further limitation to cancer therapy of brain tumors or brain metastases is the blood-tumor barrier, where tumors erect a barrier of transporters that further impede drug entry. The expression and regulation of these two transporters at these barriers, as well as tumor derived alteration in expression and/or mutation, are likely obstacles to effective therapy.

Novel role of Rac-Mid1 signaling in medial cerebellar development

Rac signaling impacts a relatively large number of downstream targets; however, few studies have established an association between Rac pathways and pathological conditions. In the present study, we generated mice with double knockout of Rac1 and Rac3 (Atoh1-Cre;Rac1^flox/flox;Rac3^-/- ) in cerebellar granule neurons (CGNs). We observed impaired tangential migration at E16.5, as well as numerous apoptotic CGNs at the deepest layer of the external granule layer (EGL) in the medial cerebellum of Atoh1-Cre;Rac1^flox/flox;Rac3^-/- mice at P8. Atoh1-Cre;Rac1^flox/flox;Rac3^-/- CGNs differentiated normally until expression of p27^kip1 and NeuN in the deep EGL at P5. Primary CGNs and cerebellar microexplants from Atoh1-Cre;Rac1^flox/flox;Rac3^-/- mice exhibited impaired neuritogenesis, which was more apparent in Map2-positive dendrites. Such findings suggest that impaired tangential migration and final differentiation of CGNs have resulted in decreased cerebellum size and agenesis of the medial internal granule layer, respectively. Furthermore, Rac depleted/deleted cells exhibited decreased levels of Mid1 and impaired mTORC1 signaling. Mid1 depletion in CGNs produced mild impairments in neuritogenesis and reductions in mTORC1 signaling. Thus, a novel Rac-signaling pathway (Rac1-Mid1-mTORC1) may be involved in medial cerebellar development.

Pyruvate Kinase Inhibits Proliferation during Postnatal Cerebellar Neurogenesis and Suppresses Medulloblastoma Formation

Aerobic glycolysis supports proliferation through unresolved mechanisms. We have previously shown that aerobic glycolysis is required for the regulated proliferation of cerebellar granule neuron progenitors (CGNP) and for the growth of CGNP-derived medulloblastoma. Blocking the initiation of glycolysis via deletion of hexokinase-2 (Hk2) disrupts CGNP proliferation and restricts medulloblastoma growth. Here, we assessed whether disrupting pyruvate kinase-M (Pkm), an enzyme that acts in the terminal steps of glycolysis, would alter CGNP metabolism, proliferation, and tumorigenesis. We observed a dichotomous pattern of PKM expression, in which postmitotic neurons throughout the brain expressed the constitutively active PKM1 isoform, while neural progenitors and medulloblastomas exclusively expressed the less active PKM2. Isoform-specific Pkm2 deletion in CGNPs blocked all Pkm expression. Pkm2-deleted CGNPs showed reduced lactate production and increased SHH-driven proliferation. ¹³C-flux analysis showed that Pkm2 deletion reduced the flow of glucose carbons into lactate and glutamate without markedly increasing glucose-to-ribose flux. Pkm2 deletion accelerated tumor formation in medulloblastoma-prone ND2:SmoA1 mice, indicating the disrupting PKM releases CGNPs from a tumor-suppressive effect. These findings show that distal and proximal disruptions of glycolysis have opposite effects on proliferation, and that efforts to block the oncogenic effect of aerobic glycolysis must target reactions upstream of PKM. Cancer Res; 77(12); 3217-30. ©2017 AACR.

Tumor Necrosis Factor Alpha-Induced Recruitment of Inflammatory Mononuclear Cells Leads to Inflammation and Altered Brain Development in Murine Cytomegalovirus-Infected Newborn Mice

Congenital human cytomegalovirus (HCMV) infection is a significant cause of abnormal neurodevelopment and long-term neurological sequelae in infants and children. Resident cell populations of the developing brain have been suggested to be more susceptible to virus-induced cytopathology, a pathway thought to contribute to the clinical outcomes following intrauterine HCMV infection. However, recent findings in a newborn mouse model of the infection in the developing brain have indicated that elevated levels of proinflammatory mediators leading to mononuclear cell activation and recruitment could underlie the abnormal neurodevelopment. In this study, we demonstrate that treatment with tumor necrosis factor alpha (TNF-α)-neutralizing antibodies decreased the frequency of CD45⁺ Ly6C^hi CD11b⁺ CCR2⁺ activated myeloid mononuclear cells (MMCs) and the levels of proinflammatory cytokines in the blood and the brains of murine CMV-infected mice. This treatment also normalized neurodevelopment in infected mice without significantly impacting the level of virus replication. These results indicate that TNF-α is a major component of the inflammatory response associated with altered neurodevelopment that follows murine CMV infection of the developing brain and that a subset of peripheral blood myeloid mononuclear cells represent a key effector cell population in this model of virus-induced inflammatory disease of the developing brain.IMPORTANCE Congenital human cytomegalovirus (HCMV) infection is the most common viral infection of the developing human fetus and can result in neurodevelopmental sequelae. Mechanisms of disease leading to neurodevelopmental deficits in infected infants remain undefined, but postulated pathways include loss of neuronal progenitor cells, damage to the developing vascular system of the brain, and altered cellular positioning. Direct virus-mediated cytopathic effects cannot explain the phenotypes of brain damage in most infected infants. Using a mouse model that recapitulates characteristics of the brain infection described in human infants, we have shown that TNF-α plays a key role in brain inflammation, including recruitment of inflammatory mononuclear cells. Neutralization of TNF-α normalized neurodevelopmental abnormalities in infected mice, providing evidence that virus-induced inflammation is a major component of disease in the developing brain. These results suggest that interventions limiting inflammation associated with the infection could potentially improve the neurologic outcome of infants infected in utero with HCMV.

Synaptogenesis in the Cerebellum of Offspring Born to Diabetic Mothers

There is increasing evidence that maternal diabetes mellitus during the pregnancy is associated with a higher risk of neurodevelopmental and neurofunctional anomalies including motor dysfunctions, learning deficits, and behavioral problems in offspring. The cerebellum is a part of the brain that has long been recognized as a center of movement balance and motor coordination. Moreover, recent studies in humans and animals have also implicated the cerebellum in cognitive processing, sensory discrimination, attention, and learning and memory. Synaptogenesis is one of the most crucial events during the development of the central nervous system. Synaptophysin (SYP) is an integral membrane protein of synaptic vesicles and is considered to be a marker for synaptic density and synaptogenesis. Here, we review the manuscripts focusing on the negative impacts of maternal diabetes in pregnancy on the expression or localization of SYP in the developing cerebellar cortex. We believe that the alteration in synaptogenesis or synapse density may be part of the cascade of events through which diabetes in pregnant women affects the newborn's cerebellum.

Glucocorticoid Effects on Cerebellar Development in a Chicken Embryo Model: Exploring Changes in PAX6 and Metalloproteinase-9 After Exposure to Dexamethasone

The developing cerebellum is vulnerable to effects of glucocorticoids and cerebellar dysfunction is associated with neurodevelopmental disorders (e.g. autism). Transcription factor PAX6 and matrix metalloproteinase-9 (MMP-9) are critical for normal cerebellar development and are highly expressed in migrating neurones. Alterations in MMP-9 and PAX6 are associated with altered cerebellar development. In the present study, we characterised the growth rate and development of the cortical layers, and further investigated how the levels of PAX6 and MMP-9, as well as glucocorticoid receptor (GR) and proliferating cell nuclear antigen (PCNA), change in the cerebellum during the foetal period [embryonic day (E)12-21] in chicken, which corresponds to the human perinatal period. Dexamethasone (DEX) was administered in ovo at E13 and E16, aiming to investigate how prenatal exposure to glucocorticoids interferes with normal development. DEX reduced foetal and cerebellar weight at E17 in a dose-dependent manner linked to a reduced level of PCNA and, over time, down-regulation of GR. We report that promoter activity of PAX6 and MMP-9 increased as a result of GR-stimulation in vitro. Prenatal DEX increased the protein level of PAX6 in a transient manner. PAX6 is reduced in mature granule neurones, and this occurred earlier in embryos exposed to DEX than in non-exposed controls. DEX exposure also led to a slow-onset down-regulation of MMP-9. Taken together, these findings indicate that excess prenatal glucocorticoid stimulation disturbs normal development of the cerebellum through mechanisms associated with reduced proliferation and accelerated maturation where PAX6 and MMP-9 play important roles.

Proneurotrophin-3 promotes cell cycle withdrawal of developing cerebellar granule cell progenitors via the p75 neurotrophin receptor

Cerebellar granule cell progenitors (GCP) proliferate extensively in the external granule layer (EGL) of the developing cerebellum prior to differentiating and migrating. Mechanisms that regulate the appropriate timing of cell cycle withdrawal of these neuronal progenitors during brain development are not well defined. The p75 neurotrophin receptor (p75(NTR)) is highly expressed in the proliferating GCPs, but is downregulated once the cells leave the cell cycle. This receptor has primarily been characterized as a death receptor for its ability to induce neuronal apoptosis following injury. Here we demonstrate a novel function for p75(NTR) in regulating proper cell cycle exit of neuronal progenitors in the developing rat and mouse EGL, which is stimulated by proNT3. In the absence of p75(NTR), GCPs continue to proliferate beyond their normal period, resulting in a larger cerebellum that persists into adulthood, with consequent motor deficits.

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

Role of Nuclear Receptors in Central Nervous System Development and Associated Diseases

The nuclear hormone receptor (NHR) superfamily is composed of a wide range of receptors involved in a myriad of important biological processes, including development, growth, metabolism, and maintenance. Regulation of such wide variety of functions requires a complex system of gene regulation that includes interaction with transcription factors, chromatin-modifying complex, and the proper recognition of ligands. NHRs are able to coordinate the expression of genes in numerous pathways simultaneously. This review focuses on the role of nuclear receptors in the central nervous system and, in particular, their role in regulating the proper development and function of the brain and the eye. In addition, the review highlights the impact of mutations in NHRs on a spectrum of human diseases from autism to retinal degeneration.

Vitronectin promotes the progress of the initial differentiation stage in cerebellar granule cells

Vitronectin (VN), which is an extracellular matrix protein, is known to be involved in the proliferation and differentiation of primary cultured cerebellar granule cell precursors (CGCPs); however, the effect of VN is not fully understood. In this study, we analyzed the effects of VN loss on the proliferation and differentiation of CGCPs in VN knockout (VNKO) mice in vivo. First, immunohistochemistry showed that VN was distributed in the region from the inner external granule layer (iEGL) through the internal granule layer (IGL) in wild-type (WT) mice. Next, we observed the formation of the cerebellar cortex using sagittal sections of VNKO mice at postnatal days (P) 5, 8 and 11. Loss of VN suppressed the ratio of NeuN, a neuronal differentiation marker, to positive cerebellar granule cells (CGCs) in the external granule layer (EGL) and the ratio of CGCs in the IGL at P8, indicating that the loss of VN suppresses the differentiation into CGCs. However, the loss of VN did not significantly affect the proliferation of CGCPs. Next, the effect of VN loss on the initial differentiation stage of CGCPs was examined. The loss of VN increased the expression levels of Transient axonal glycoprotein 1 (TAG1), a marker of neurons in the initial differentiation stage, in the cerebella of VNKO mice at P5 and 8 and increased the ratio of TAG1-positive cells in the primary culture of VNKO-derived CGCPs, indicating that the loss of VN accumulates the CGCPs in the initial differentiation stage. Taken together, these results demonstrate that VN promotes the progress of the initial differentiation stage of CGCPs.

Development and regulation of chloride homeostasis in the central nervous system

γ-Aminobutyric acid (GABA) is the main inhibitory neurotransmitter of the mature central nervous system (CNS). The developmental switch of GABAergic transmission from excitation to inhibition is induced by changes in Cl⁻ gradients, which are generated by cation-Cl⁻ co-transporters. An accumulation of Cl⁻ by the Na⁺-K⁺-2Cl⁻ co-transporter (NKCC1) increases the intracellular Cl⁻ concentration ([Cl⁻]_i) such that GABA depolarizes neuronal precursors and immature neurons. The subsequent ontogenetic switch, i.e., upregulation of the Cl⁻-extruder KCC2, which is a neuron-specific K⁺-Cl⁻ co-transporter, with or without downregulation of NKCC1, results in low [Cl⁻]_i levels and the hyperpolarizing action of GABA in mature neurons. Development of Cl⁻ homeostasis depends on developmental changes in NKCC1 and KCC2 expression. Generally, developmental shifts (decreases) in [Cl⁻]_i parallel the maturation of the nervous system, e.g., early in the spinal cord, hypothalamus and thalamus, followed by the limbic system, and last in the neocortex. There are several regulators of KCC2 and/or NKCC1 expression, including brain-derived neurotrophic factor (BDNF), insulin-like growth factor (IGF), and cystic fibrosis transmembrane conductance regulator (CFTR). Therefore, regionally different expression of these regulators may also contribute to the regional developmental shifts of Cl⁻ homeostasis. KCC2 and NKCC1 functions are also regulated by phosphorylation by enzymes such as PKC, Src-family tyrosine kinases, and WNK1–4 and their downstream effectors STE20/SPS1-related proline/alanine-rich kinase (SPAK)-oxidative stress responsive kinase-1 (OSR1). In addition, activation of these kinases is modulated by humoral factors such as estrogen and taurine. Because these transporters use the electrochemical driving force of Na⁺ and K⁺ ions, topographical interaction with the Na⁺-K⁺ ATPase and its modulators such as creatine kinase (CK) should modulate functions of Cl⁻ transporters. Therefore, regional developmental regulation of these regulators and modulators of Cl⁻ transporters may also play a pivotal role in the development of Cl⁻ homeostasis.

Aryl hydrocarbon receptor deletion in cerebellar granule neuron precursors impairs neurogenesis

The aryl hydrocarbon receptor (AhR) is a ligand-activated member of the basic-helix-loop-helix/PER-ARNT-SIM(PAS) transcription factor superfamily that also mediates the toxicity of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Increasing evidence suggests that AhR influences the development of many tissues, including the central nervous system. Our previous studies suggest that sustained AhR activation by TCDD and/or AhR deletion disrupts cerebellar granule neuron precursor (GNP) development. In the current study, to determine whether endogenous AhR controls GNP development in a cell-autonomous manner, we created a GNP-specific AhR deletion mouse, AhR(fx/fx) /Math1(CRE/+) (AhR CKO). Selective AhR deletion in GNPs produced abnormalities in proliferation and differentiation. Specifically, fewer GNPs were engaged in S-phase, as demonstrated by ∼25% reductions in thymidine (in vitro) and Bromodeoxyuridine (in vivo) incorporation. Furthermore, total granule neuron numbers in the internal granule layer at PND21 and PND60 were diminished in AhR conditional knockout (CKO) mice compared with controls. Conversely, differentiation was enhanced, including ∼40% increase in neurite outgrowth and 50% increase in GABARα6 receptor expression in deletion mutants. Our results suggest that AhR activity plays a role in regulating granule neuron number and differentiation, possibly by coordinating this GNP developmental transition. These studies provide novel insights for understanding the normal roles of AhR signaling during cerebellar granule cell neurogenesis and may have important implications for the effects of environmental factors in cerebellar dysgenesis.

Expression of mouse Dab2ip transcript variants and gene methylation during brain development

Dab2ip (DOC-2/DAB2 interacting protein) is a RasGAP protein which shows a growth-inhibitory effect in human prostate cancer cell lines. Recent studies have shown that Dab2ip also plays an important role in regulating dendrite development and neuronal migration during brain development. In this study, we provide a more complete description of the mouse Dab2ip (mDab2ip) gene locus and examined DNA methylation and expression of Dab2ip during cerebellar development. Analysis of cDNA sequences in public databases revealed a total of 20 possible exons for mDab2ip gene, spanning over 172kb. Using Cap Analysis of Gene Expression (CAGE) data available through FANTOM5 project, we deduced five different transcription start sites for mDab2ip. Here, we characterized three different mDab2ip transcript variants beginning with exon 1. These transcripts varied by the presence or absence of exons 3 and 5, which encode a putative nuclear localization signal and the N-terminal region of a PH-domain, respectively. The 5' region of the mDab2ip gene contains three putative CpG islands (CpG131, CpG54, and CpG85). Interestingly, CpG54 and CpG85 are localized on exons 3 and 5. Bisulfate DNA sequencing showed that methylation level of CpG54 remained constant whereas methylation of CpG85 increased during cerebellar development. Real-time PCR analysis showed that the proportion of PH-domain containing mDab2ip transcripts increased during cerebellar development, in correlation with the increase in CpG85 methylation. These data suggest that site-specific methylation of mDab2ip gene during cerebellar development may play a role in inclusion of exon 5, resulting in a Dab2ip transcript variant that encodes a full pleckstrin homology (PH) domain.

ATOH1 Can Regulate the Tumorigenicity of Gastric Cancer Cells by Inducing the Differentiation of Cancer Stem Cells

Cancer stem cells (CSCs) have been shown to mediate tumorigenicity, chemo-resistance, radio-resistance and metastasis, which suggest they be considered therapeutic targets. Because their differentiated daughter cells are no longer tumorigenic, to induce the differentiation of CSCs can be one of strategies which can eradicate CSCs. Here we show that ATOH1 can induce the differentiation of gastric cancer stem cells (GCSCs). Real time PCR and western blot analysis showed that ATOH1 was induced during the differentiation of GCSCs. Furthermore, the lentivirus-induced overexpression of ATOH1 in GCSCs and in gastric cancer cell lines significantly induced differentiation, reduced proliferation and sphere formation, and reduced in vivo tumor formation in the subcutaneous injection and liver metastasis xenograft models. These results suggest ATOH1 be considered for the development of a differentiation therapy for gastric cancer.

Serpine2/PN-1 Is Required for Proliferative Expansion of Pre-Neoplastic Lesions and Malignant Progression to Medulloblastoma

Background

Medulloblastomas are malignant childhood brain tumors that arise due to the aberrant activity of developmental pathways during postnatal cerebellar development and in adult humans. Transcriptome analysis has identified four major medulloblastoma subgroups. One of them, the Sonic hedgehog (SHH) subgroup, is caused by aberrant Hedgehog signal transduction due to mutations in the Patched1 (PTCH1) receptor or downstream effectors. Mice carrying a Patched-1 null allele (Ptch1^∆/+) are a good model to study the alterations underlying medulloblastoma development as a consequence of aberrant Hedgehog pathway activity.

Results

Transcriptome analysis of human medulloblastomas shows that SERPINE2, also called Protease Nexin-1 (PN-1) is overexpressed in most medulloblastomas, in particular in the SHH and WNT subgroups. As siRNA-mediated lowering of SERPINE2/PN-1 in human medulloblastoma DAOY cells reduces cell proliferation, we analyzed its potential involvement in medulloblastoma development using the Ptch1^∆/+ mouse model. In Ptch1^∆/+ mice, medulloblastomas arise as a consequence of aberrant Hedgehog pathway activity. Genetic reduction of Serpine2/Pn-1 interferes with medulloblastoma development in Ptch1^∆/+ mice, as ~60% of the pre-neoplastic lesions (PNLs) fail to develop into medulloblastomas and remain as small cerebellar nodules. In particular the transcription factor Atoh1, whose expression is essential for development of SHH subgroup medulloblastomas is lost. Comparative molecular analysis reveals the distinct nature of the PNLs in young Ptch1^∆/+Pn-1^Δ/+ mice. The remaining wild-type Ptch1 allele escapes transcriptional silencing in most cases and the aberrant Hedgehog pathway activity is normalized. Furthermore, cell proliferation and the expression of the cell-cycle regulators Mycn and Cdk6 are significantly reduced in PNLs of Ptch1^∆/+Pn-1^Δ/+ mice.

Conclusions

Our analysis provides genetic evidence that aberrant Serpine2/Pn-1 is required for proliferation of human and mouse medulloblastoma cells. In summary, our analysis shows that Serpine2/PN-1 boosts malignant progression of PNLs to medulloblastomas, in which the Hedgehog pathway is activated in a SHH ligand-independent manner.

CbGRiTS: cerebellar gene regulation in time and space

The mammalian CNS is one of the most complex biological systems to understand at the molecular level. The temporal information from time series transcriptome analysis can serve as a potent source of associative information between developmental processes and regulatory genes. Here, we introduce a new transcriptome database called, Cerebellar Gene Regulation in Time and Space (CbGRiTS). This dataset is populated with transcriptome data across embryonic and postnatal development from two standard mouse strains, C57BL/6J and DBA/2J, several recombinant inbred lines and cerebellar mutant strains. Users can evaluate expression profiles across cerebellar development in a deep time series with graphical interfaces for data exploration and link-out to anatomical expression databases. We present three analytical approaches that take advantage of specific aspects of the time series for transcriptome analysis. We demonstrate the use of CbGRiTS dataset as a community resource to explore patterns of gene expression and develop hypotheses concerning gene regulatory networks in brain development.

Calorie restriction and corticosterone elevation during lactation can each modulate adult male fear and anxiety-like behaviour

Early life events, such as calorie restriction (CR) and elevated glucocorticoids, can calibrate the lifelong behavioural and physiological profile of an individual. Stress reactivity in adulthood is particularly sensitive to early life events; however, the consequence to fear and anxiety-like behaviour is less clear. Consequently, the current study sought to examine the effects of post-natal CR and glucocorticoid elevation, long considered powerful programming stimuli, on the subsequent fear and anxiety behaviour of the adult offspring. Rat dams received either corticosterone (200 μg/ml) supplementation in drinking water (CORT) or a 25% CR from post-natal day (PND) 1 to 11. Responses to the elevated plus maze (EPM), open field and a predator odour (TMT; 2,5-dihydro-2,4,5-trimethylthiazoline) were characterised in the adult male offspring. Both treatment conditions resulted in enhanced fear responses to TMT, characterised by heightened risk assessment and increased avoidance of TMT. CORT nursed offspring further demonstrated an anxiogenic profile in the open field. Basal hypothalamic-pituitary-adrenal function was unchanged in CORT adult offspring, whilst corticosterone concentration was elevated by post-natal CR. CR and CORT treated dams both exhibited greater anxiety-like behaviour in the EPM. A modest and temporary enhancement of maternal care was observed in CR and CORT treated dams, with CR dams further exhibiting rapid pup retrieval latencies. The results indicate enhanced emotionality in the adult male progeny of dams exposed to CR and corticosterone supplementation during the post-natal period. The modest enhancement of maternal care observed by both treatments is unlikely to have influenced the behavioural profile of the offspring.

Specification of spatial identities of cerebellar neuron progenitors by ptf1a and atoh1 for proper production of GABAergic and glutamatergic neurons

In the cerebellum, the bHLH transcription factors Ptf1a and Atoh1 are expressed in distinct neuroepithelial regions, the ventricular zone (VZ) and the rhombic lip (RL), and are required for producing GABAergic and glutamatergic neurons, respectively. However, it is unclear whether Ptf1a or Atoh1 is sufficient for specifying GABAergic or glutamatergic neuronal fates. To test this, we generated two novel knock-in mouse lines, Ptf1a(Atoh1) and Atoh1(Ptf1a), that are designed to express Atoh1 and Ptf1a ectopically in the VZ and RL, respectively. In Ptf1a(Atoh1) embryos, ectopically Atoh1-expressing VZ cells produced glutamatergic neurons, including granule cells and deep cerebellar nuclei neurons. Correspondingly, in Atoh1(Ptf1a) animals, ectopically Ptf1a-expressing RL cells produced GABAergic populations, such as Purkinje cells and GABAergic interneurons. Consistent results were also obtained from in utero electroporation of Ptf1a or Atoh1 into embryonic cerebella, suggesting that Ptf1a and Atoh1 are essential and sufficient for GABAergic versus glutamatergic specification in the neuroepithelium. Furthermore, birthdating analyses with BrdU in the knock-in mice or with electroporation studies showed that ectopically produced fate-changed neuronal types were generated at temporal schedules closely simulating those of the wild-type RL and VZ, suggesting that the VZ and RL share common temporal information. Observations of knock-in brains as well as electroporated brains revealed that Ptf1a and Atoh1 mutually negatively regulate their expression, probably contributing to formation of non-overlapping neuroepithelial domains. These findings suggest that Ptf1a and Atoh1 specify spatial identities of cerebellar neuron progenitors in the neuroepithelium, leading to appropriate production of GABAergic and glutamatergic neurons, respectively.

Genetic manipulation of cerebellar granule neurons in vitro and in vivo to study neuronal morphology and migration

Developmental events in the brain including neuronal morphogenesis and migration are highly orchestrated processes. In vitro and in vivo analyses allow for an in-depth characterization to identify pathways involved in these events. Cerebellar granule neurons (CGNs) that are derived from the developing cerebellum are an ideal model system that allows for morphological analyses. Here, we describe a method of how to genetically manipulate CGNs and how to study axono- and dendritogenesis of individual neurons. With this method the effects of RNA interference, overexpression or small molecules can be compared to control neurons. In addition, the rodent cerebellar cortex is an easily accessible in vivo system owing to its predominant postnatal development. We also present an in vivo electroporation technique to genetically manipulate the developing cerebella and describe subsequent cerebellar analyses to assess neuronal morphology and migration.

Regional differences in the expression of K(+)-Cl(-) 2 cotransporter in the developing rat cortex

The type 2 potassium-chloride cotransporter (KCC2) is the main regulator of intracellular chloride concentration in CNS neurons, and plays a crucial role in spine development that is independent of its ion cotransport function. The expression pattern of KCC2 is upregulated during postnatal development showing area and layer-specific differences in distinct brain areas. We examined the regional and ultrastructural localisation of KCC2 in various areas of developing neocortex and paleocortex during the first two postnatal weeks. Light-microscopy examination revealed diffuse neuropil and discrete funnel-shaped dendritic labelling in the piriform and entorhinal cortices at birth. Subsequently, during the beginning of the first postnatal week, diffuse KCC2 labelling gradually started to appear in the superficial layers of the neocortex while the punctate-like labelling of dendrites in the piriform, entorhinal and perirhinal cortices become more pronounced. By the end of the first postnatal week, discrete dendritic expression of KCC2 was visible in all neocortical and paleocortical areas. The expression level did not change during the second postnatal week suggesting that, in contrast to hippocampus, adult pattern of KCC2 in the cortical cells is already established by the end of the first postnatal week. Quantitative electron microscopy examination revealed that in superficial layers of both neo- and paleocortex, the majority of KCC2 signal was plasma membrane associated but the number of transport vesicle-associated immunosignal increased with development. In deep layers, KCC2 immunolabeling was evenly distributed in plasma membrane and transport vesicles showing no obvious change with maturation. The number of KCC2 immunogold particles increased in dendritic spines with no association with synapses. This observation points to the dual role of KCC2 in spine genesis and ion cotransport.

Otx2 cell-autonomously determines dorsal mesencephalon versus cerebellum fate independently of isthmic organizing activity

During embryonic development, the rostral neuroectoderm is regionalized into broad areas that are subsequently subdivided into progenitor compartments with specialized identity and fate. These events are controlled by signals emitted by organizing centers and interpreted by target progenitors, which activate superimposing waves of intrinsic factors restricting their identity and fate. The transcription factor Otx2 plays a crucial role in mesencephalic development by positioning the midbrain-hindbrain boundary (MHB) and its organizing activity. Here, we investigated whether Otx2 is cell-autonomously required to control identity and fate of dorsal mesencephalic progenitors. With this aim, we have inactivated Otx2 in the Pax7(+) dorsal mesencephalic domain, previously named m1, without affecting MHB integrity. We found that the Pax7(+) m1 domain can be further subdivided into a dorsal Zic1(+) m1a and a ventral Zic1(-) m1b sub-domain. Loss of Otx2 in the m1a (Pax7(+) Zic1(+)) sub-domain impairs the identity and fate of progenitors, which undergo a full switch into a coordinated cerebellum differentiation program. By contrast, in the m1b sub-domain (Pax7(+) Zic1(-)) Otx2 is prevalently required for post-mitotic transition of mesencephalic GABAergic precursors. Moreover, genetic cell fate, BrdU cell labeling and Otx2 conditional inactivation experiments indicate that in Otx2 mutants all ectopic cerebellar cell types, including external granule cell layer (EGL) precursors, originate from the m1a progenitor sub-domain and that reprogramming of mesencephalic precursors into EGL or cerebellar GABAergic progenitors depends on temporal sensitivity to Otx2 ablation. Together, these findings indicate that Otx2 intrinsically controls different aspects of dorsal mesencephalic neurogenesis. In this context, Otx2 is cell-autonomously required in the m1a sub-domain to suppress cerebellar fate and promote mesencephalic differentiation independently of the MHB organizing activity.

SIP1 expression patterns in brain investigated by generating a SIP1-EGFP reporter knock-in mouse

A loss of function of SIP1 (Smad interacting protein 1) in the mouse as well as in human of Mowat-Wilson syndrome results in severe and multiple defects in neural tissue development, especially in the brain. However, no detailed expression analysis of SIP1 during brain development has been previously reported. In this study, we describe the generation of an EGFP knock-in reporter mouse for the Sip1 locus and our subsequent analysis of SIP1-EGFP fusion protein expression during brain development. SIP1-EGFP expression was observed in the pyramidal neurons of the hippocampus, the dentate gyrus, and the postmitotic neurons in the cerebral cortex. In layer 5 of the cerebral cortex, SIP1-EGFP expression was complementary to the Ctip2-expressing neurons, most of which are thought to be the cortico-spinal neurons. This suggested that SIP1-EGFP expressing cells might have the specific trajectory targets other than the spinal region. We further observed SIP1-EGFP expression in oligodendrocytes of the corpus callosum and fimbria, Bergmann glial cells of the cerebellum, the olfactory bulb, and in the serotonergic and dopaminergic neurons of the raphe nuclei in the brainstem. These findings may help to clarify the unknown roles of SIP1 in these cells and the pathoetiology of Mowat-Wilson syndrome.

WNT3 inhibits cerebellar granule neuron progenitor proliferation and medulloblastoma formation via MAPK activation

During normal cerebellar development, the remarkable expansion of granule cell progenitors (GCPs) generates a population of granule neurons that outnumbers the total neuronal population of the cerebral cortex, and provides a model for identifying signaling pathways that may be defective in medulloblastoma. While many studies focus on identifying pathways that promote growth of GCPs, a critical unanswered question concerns the identification of signaling pathways that block mitogenic stimulation and induce early steps in differentiation. Here we identify WNT3 as a novel suppressor of GCP proliferation during cerebellar development and an inhibitor of medulloblastoma growth in mice. WNT3, produced in early postnatal cerebellum, inhibits GCP proliferation by down-regulating pro-proliferative target genes of the mitogen Sonic Hedgehog (SHH) and the bHLH transcription factor Atoh1. WNT3 suppresses GCP growth through a non-canonical Wnt signaling pathway, activating prototypic mitogen-activated protein kinases (MAPKs), the Ras-dependent extracellular-signal-regulated kinases 1/2 (ERK1/2) and ERK5, instead of the classical β-catenin pathway. Inhibition of MAPK activity using a MAPK kinase (MEK) inhibitor reversed the inhibitory effect of WNT3 on GCP proliferation. Importantly, WNT3 inhibits proliferation of medulloblastoma tumor growth in mouse models by a similar mechanism. Thus, the present study suggests a novel role for WNT3 as a regulator of neurogenesis and repressor of neural tumors.

Impaired structural and functional development of cerebellum following gestational exposure of deltamethrin in rats: role of reelin

Reelin is an extracellular matrix molecule that is involved in the normal development of the cerebellar lamination, Bergmann glial fibres alignment, Purkinje cell monolayer arrangement and granule cell migration. In this study, we have examined the effects of maternal exposure of deltamethrin (DLT), a type II pyrethroid insecticide, on the structural and functional development of rat cerebellum during postnatal life. DLT (0.75 mg/kg body weight, intraperitoneally dissolved in dimethylsulphoxide) was administered in timed pregnant rats during two different gestational time periods, i.e. gestational days of 7-10 and 11-14, respectively. In DLT exposed rats, a significant overexpression of reelin was observed in the cells of the external granule cell layer (EGL) and internal granule cell layer along with an ectopic expression of reelin in the EGL as well as in the migrating granule cells just below the EGL, revealing an arrest of granule cell migration in this zone. Mis-orientation and hypertrophy of the Bergmann glial fibres further hampered the journey of the granule cells to their final destination. Possibly reelin overexpression also caused misalignment of the Purkinje cells and inhibited the neurite growth leading to a significant decrease in the spine density, main dendritic length and width of the dendritic arbour. Thus, it is proposed that the DLT exerts its neurotoxic effects possibly via the intracellular accumulation and low release of reelin leading to an impaired granule cell and Purkinje cell migration, inhibition of neurite outgrowth and reduced spine density. Such impaired cerebellar development leads to motor coordination deficits.

Culturing mouse cerebellar granule neurons

The cerebellum plays an important role in motor control, motor skill acquisition, memory and learning among other brain functions. In rodents, cerebellar development continues after birth, characterized by the maturation of granule neurons. Cerebellar granule neurons (CGNs) are the most abundant neuronal type in the central nervous system, and they provide an excellent model for investigating molecular, -cellular, and physiological mechanisms underlying neuronal development as well as neural circuitry linked to behavior. Here we describe a procedure to isolate and culture CGNs from postnatal day 6 mice. These cultures can be used to examine numerous aspects of CGN differentiation, electrophysiology, and function.

Inducible and reversible regulation of endogenous gene in mouse

Methods for generating loss-of-function mutations, such as conventional or conditional gene knockout, are widely used in deciphering gene function in vivo. By contrast, inducible and reversible regulation of endogenous gene expression has not been well established. Using a mouse model, we demonstrate that a chimeric transcriptional repressor molecule (tTS) can reversibly inhibit the expression of an endogenous gene, Nmyc. In this system, a tetracycline response element (TRE) artificially inserted near the target gene’s promoter region turns the gene on and off in a tetracycline-inducible manner. Nmyc^TRE mice were generated by inserting a TRE into the first intron of Nmyc by the knockin technique. Nmyc^TRE mice were crossed to tTS transgenic mice to produce Nmyc^TRE/TRE: tTS embryos. In these embryos, tTS blocked Nmyc expression, and embryonic lethality was observed at E11.5d. When the dam was exposed to drinking water containing doxycycline (dox), normal endogenous Nmyc expression was rescued, and the embryo survived to birth. This novel genetic modification strategy based on the tTS–dox system for inducible and reversible regulation of endogenous mouse genes will be a powerful tool to investigate target genes that cause embryonic lethality or other defects where reversible regulation or temporary shutdown of the target gene is needed.

The CSF-1 receptor ligands IL-34 and CSF-1 exhibit distinct developmental brain expression patterns and regulate neural progenitor cell maintenance and maturation

The CSF-1 receptor (CSF-1R) regulates CNS microglial development. However, the localization and developmental roles of this receptor and its ligands, IL-34 and CSF-1, in the brain are poorly understood. Here we show that compared to wild type mice, CSF-1R-deficient (Csf1r-/-) mice have smaller brains of greater mass. They further exhibit an expansion of lateral ventricle size, an atrophy of the olfactory bulb and a failure of midline crossing of callosal axons. In brain, IL-34 exhibited a broader regional expression than CSF-1, mostly without overlap. Expression of IL-34, CSF-1 and the CSF-1R were maximal during early postnatal development. However, in contrast to the expression of its ligands, CSF-1R expression was very low in adult brain. Postnatal neocortical expression showed that CSF-1 was expressed in layer VI, whereas IL-34 was expressed in the meninges and layers II-V. The broader expression of IL-34 is consistent with its previously implicated role in microglial development. The differential expression of CSF-1R ligands, with respect to CSF-1R expression, could reflect their CSF-1R-independent signaling. Csf1r-/- mice displayed increased proliferation and apoptosis of neocortical progenitors and reduced differentiation of specific excitatory neuronal subtypes. Indeed, addition of CSF-1 or IL-34 to microglia-free, CSF-1R-expressing dorsal forebrain clonal cultures, suppressed progenitor self-renewal and enhanced neuronal differentiation. Consistent with a neural developmental role for the CSF-1R, ablation of the Csf1r gene in Nestin-positive neural progenitors led to a smaller brain size, an expanded neural progenitor pool and elevated cellular apoptosis in cortical forebrain. Thus our results also indicate novel roles for the CSF-1R in the regulation of corticogenesis.

Mitochondrial division ensures the survival of postmitotic neurons by suppressing oxidative damage

Mitochondria divide and fuse continuously, and the balance between these two processes regulates mitochondrial shape. Alterations in mitochondrial dynamics are associated with neurodegenerative diseases. Here we investigate the physiological and cellular functions of mitochondrial division in postmitotic neurons using in vivo and in vitro gene knockout for the mitochondrial division protein Drp1. When mouse Drp1 was deleted in postmitotic Purkinje cells in the cerebellum, mitochondrial tubules elongated due to excess fusion, became large spheres due to oxidative damage, accumulated ubiquitin and mitophagy markers, and lost respiratory function, leading to neurodegeneration. Ubiquitination of mitochondria was independent of the E3 ubiquitin ligase parkin in Purkinje cells lacking Drp1. Treatment with antioxidants rescued mitochondrial swelling and cell death in Drp1KO Purkinje cells. Moreover, hydrogen peroxide converted elongated tubules into large spheres in Drp1KO fibroblasts. Our findings suggest that mitochondrial division serves as a quality control mechanism to suppress oxidative damage and thus promote neuronal survival.

Tensor-based morphometry and stereology reveal brain pathology in the complexin1 knockout mouse

Complexins (Cplxs) are small, soluble, regulatory proteins that bind reversibly to the SNARE complex and modulate synaptic vesicle release. Cplx1 knockout mice (Cplx1(-/-)) have the earliest known onset of ataxia seen in a mouse model, although hitherto no histopathology has been described in these mice. Nevertheless, the profound neurological phenotype displayed by Cplx1(-/-) mutants suggests that significant functional abnormalities must be present in these animals. In this study, MRI was used to automatically detect regions where structural differences were not obvious when using a traditional histological approach. Tensor-based morphometry of Cplx1(-/-) mouse brains showed selective volume loss from the thalamus and cerebellum. Stereological analysis of Cplx1(-/-) and Cplx1(+/+) mice brain slices confirmed the volume loss in the thalamus as well as loss in some lobules of the cerebellum. Finally, stereology was used to show that there was loss of cerebellar granule cells in Cplx1(-/-) mice when compared to Cplx1(+/+) animals. Our study is the first to describe pathological changes in Cplx1(-/-) mouse brain. We suggest that the ataxia in Cplx1(-/-) mice is likely to be due to pathological changes in both cerebellum and thalamus. Reduced levels of Cplx proteins have been reported in brains of patients with neurodegenerative diseases. Therefore, understanding the effects of Cplx depletion in brains from Cplx1(-/-) mice may also shed light on the mechanisms underlying pathophysiology in disorders in which loss of Cplx1 occurs.

The fetal cerebellum: development and common malformations

The cerebellum undergoes a protracted development, making it particularly vulnerable to a broad spectrum of developmental events. Acquired destructive and hemorrhagic insults may also occur. The main steps of cerebellar development are reviewed. The normal imaging patterns of the cerebellum in prenatal ultrasound and magnetic resonance imaging (MRI) are described with emphasis on the limitations of these modalities. Because of confusion in the literature regarding the terminology used for cerebellar malformations, some terms (agenesis, hypoplasia, dysplasia, and atrophy) are clarified. Three main pathologic settings are considered and the main diagnoses that can be suggested are described: retrocerebellar fluid enlargement with normal or abnormal biometry (Dandy-Walker malformation, Blake pouch cyst, vermian agenesis), partially or globally decreased cerebellar biometry (cerebellar hypoplasia, agenesis, rhombencephalosynapsis, ischemic and/or hemorrhagic damage), partially or globally abnormal cerebellar echogenicity (ischemic and/or hemorrhagic damage, cerebellar dysplasia, capillary telangiectasia). The appropriate timing for performing MRI is also discussed.

Neuroimaging of Dandy-Walker malformation: new concepts

Dandy-Walker malformation (DWM) is the most common human cerebellar malformation, characterized by hypoplasia of the cerebellar vermis, cystic dilation of the fourth ventricle, and an enlarged posterior fossa with upward displacement of the lateral sinuses, tentorium, and torcular. Although its pathogenesis is not completely understood, there are several genetic loci related to DWM as well as syndromic malformations and congenital infections. Dandy-Walker malformation is associated with other central nervous system abnormalities, including dysgenesis of corpus callosum, ectopic brain tissue, holoprosencephaly, and neural tube defects. Hydrocephalus plays an important role in the development of symptoms and neurological outcome in patients with DWM, and the aim of surgical treatment is usually the control of hydrocephalus and the posterior fossa cyst. Imaging modalities, especially magnetic resonance imaging, are crucial for the diagnosis of DWM and distinguishing this disorder from other cystic posterior fossa lesions. Persistent Blake's cyst is seen as a retrocerebellar fluid collection with cerebrospinal fluid signal intensity and a median line communication with the fourth ventricle, commonly associated with hydrocephalus. Mega cisterna magna presents as an extraaxial fluid collection posteroinferior to an intact cerebellum. Retrocerebellar arachnoid cysts frequently compress the cerebellar hemispheres and the fourth ventricle. Patients with DWM show an enlarged posterior fossa filled with a cystic structure that communicates freely with the fourth ventricle and hypoplastic vermis. Comprehension of hindbrain embryology is of utmost importance for understanding the cerebellar malformations, including DWM, and other related entities.

Early protein malnutrition disrupts cerebellar development and impairs motor coordination

Maternal malnutrition affects every aspect of fetal development. The present study asked the question whether a low-protein diet of the mother could result in motor deficits in the offspring. Further, to examine whether cerebellar pathology was correlated with motor deficits, several parameters of the postnatal development of the cerebellum were assayed. This is especially important because the development of the cerebellum is unique in that the time scale of development is protracted compared with that of the cortex or hippocampus. The most important result of the study is that animals born to protein-deficient mothers showed significant delays in motor development as assessed by rotarod and gait analysis. These animals also showed reduced cell proliferation and reduced thickness in the external granular layer. There was a reduction in the number of calbindin-positive Purkinje cells (PC) and granular cells in the internal granular layer. However, glial fibrillary acidic protein-positive population including Bergmann glia remained unaffected. We therefore conclude that the development of the granular cell layer and the PC is specifically prone to the effects of protein malnutrition potentially due to their protracted developmental period from approximately embryonic day 11 to 13 until about the third postnatal week.

Knockout of G protein β5 impairs brain development and causes multiple neurologic abnormalities in mice

Gβ5 is a divergent member of the signal-transducing G protein β subunit family encoded by GNB5 and expressed principally in brain and neuronal tissue. Among heterotrimeric Gβ isoforms, Gβ5 is unique in its ability to heterodimerize with members of the R7 subfamily of the regulator of G protein signaling proteins that contain G protein-γ like domains. Previous studies employing Gnb5 knockout (KO) mice have shown that Gβ5 is an essential stabilizer of such regulator of G protein signaling proteins and regulates the deactivation of retinal phototransduction and the proper functioning of retinal bipolar cells. However, little is known of the function of Gβ5 in the brain outside the visual system. We show here that mice lacking Gβ5 have a markedly abnormal neurologic phenotype that includes impaired development, tiptoe-walking, motor learning and coordination deficiencies, and hyperactivity. We further show that Gβ5-deficient mice have abnormalities of neuronal development in cerebellum and hippocampus. We find that the expression of both mRNA and protein from multiple neuronal genes is dysregulated in Gnb5 KO mice. Taken together with previous observations from Gnb5 KO mice, our findings suggest a model in which Gβ5 regulates dendritic arborization and/or synapse formation during development, in part by effects on gene expression.

The tumor biology and molecular characteristics of medulloblastoma identifying prognostic factors associated with survival outcomes and prognosis

Medulloblastomas (MB) are highly aggressive primitive neuroectodermal tumors (PNET) usually located in the posterior fossa. Current treatment for MBs, which includes a combination of surgery, chemotherapy and radiation, remain challenging especially in younger patients. However, advances in the understanding of regulatory pathways in cerebellar development have elucidated possible areas of dysfunction involved in tumorigenesis. Multiple studies have demonstrated the importance of the sonic hedgehog, Wnt, and Notch pathways in MB pathogenesis at the molecular level. While staging and prognosis are often based on the Chang classification system, future algorithms will involve identifying molecular markers in order to allow for more specific risk stratifications of various MB subtypes and provide improved correlation with staging and prognosis. Future development of novel therapies that target the heterogeneity of MB and are tailored to the tumor's unique molecular profile may yield improved outcomes for these patients.

The F-box protein Fbw7 is required for cerebellar development

The F-box protein Fbw7 (also known as Fbxw7, hCdc4 and Sel-10) functions as a substrate recognition component of a SCF-type E3 ubiquitin ligase. SCF(Fbw7) facilitates polyubiquitination and subsequent degradation of various proteins such as Notch, cyclin E, c-Myc and c-Jun. Fbw7 is highly expressed in the nervous system and controls neural stem cell differentiation and apoptosis via Notch and c-Jun during embryonic development (Hoeck et al., 2010). Fbw7 deletion in the neural lineage is perinatal lethal and thus prohibits studying the role of Fbw7 in the adult nervous system. fbw7 mRNA is highly expressed in the postnatal brain and to gain insights into the function of Fbw7 in postnatal neurogenesis we analysed Fbw7 function in the cerebellum. We generated conditional Fbw7-knockout mice (fbw7(∆Cb)) by inactivating Fbw7 specifically in the cerebellar anlage. This resulted in decreased cerebellar size, reduced Purkinje cell number and defects in axonal arborisation. Moreover, Fbw7-deficient cerebella showed supranumeral fissures and aberrant progenitor cell migration. Protein levels of the Fbw7 substrates Notch1 and N-terminally phosphorylated c-Jun were upregulated in fbw7(∆Cb) mice. Concomitant deletion of c-Jun, and also the junAA knock-in mutation which specifically abrogates c-Jun N-terminal phosphorylation, rescued Purkinje cell numbers and arborisation in the fbw7(∆Cb) background. Taken together these data demonstrate that Fbw7 is essential during cerebellar development, and identify N-terminally phosphorylated c-Jun as an important substrate of SCF(Fbw7) during neurogenesis.

Spatiotemporal fate map of neurogenin1 (Neurog1) lineages in the mouse central nervous system

Neurog1 (Ngn1, Neurod3, neurogenin1) is a basic helix-loop-helix (bHLH) transcription factor essential for neuronal differentiation and subtype specification during embryogenesis. Due to the transient expression of Neurog1 and extensive migration of neuronal precursors, it has been challenging to understand the full complement of Neurog1 lineage cells throughout the central nervous system (CNS). Here we labeled and followed Neurog1 lineages using inducible Cre-flox recombination systems with Neurog1-Cre and Neurog1-CreER(T2) BAC (bacterial artificial chromosome) transgenic mice. Neurog1 lineage cells are restricted to neuronal fates and contribute to diverse but discrete populations in each brain region. In the forebrain, Neurog1 lineages include mitral cells and glutamatergic interneurons in the olfactory bulb, pyramidal and granule neurons in the hippocampus, and pyramidal cells in the cortex. In addition, most of the thalamus, but not the hypothalamus, arises from Neurog1 progenitors. Although Neurog1 lineages are largely restricted to glutamatergic neurons, there are multiple exceptions including Purkinje cells and other GABAergic neurons in the cerebellum. This study provides the first overview of the spatiotemporal fate map of Neurog1 lineages in the CNS.

Upregulation of E2F1 in cerebellar neuroprogenitor cells and cell cycle arrest during postnatal brain development

In the developing cerebellum, proliferation of granular neuroprogenitor (GNP) cells lasts until the early postnatal stages when terminal maturation of the cerebellar cortex occurs. GNPs are considered cell targets for neoplastic transformation, and disturbances in cerebellar GNP cell proliferation may contribute to the development of pediatric medulloblastoma. At the molecular level, proliferation of GNPs is regulated through an orchestrated action of the SHH, NOTCH, and WNT pathways, but the underlying mechanisms still need to be dissected. Here, we report that expression of the E2F1 transcription factor in rat GNPs is inversely correlated with cell proliferation rate during postnatal development, as opposed to its traditional SHH-dependent induction of cell cycle. Proliferation of GNPs peaked at postnatal day 3 (P3), with a subsequent continuing decrease in proliferation rates occurring until P12. Such gradual decline in proliferating neuroprogenitors paralleled the extent of cerebellum maturation confirmed by histological analysis with cresyl violet staining and temporal expression profiling of SHH, NOTCH2, and WNT4 genes. A time course analysis of E2F1 expression in GNPs revealed significantly increased levels at P12, correlating with decreased cell proliferation. Expression of the cell cycle inhibitor p18 ( Ink4c ), a target of E2F1, was also significantly higher at P12. Conversely, increased E2F1 expression did not correlate with either SMAC/DIABLO and BCL2 expression profiles or apoptosis of cerebellar cells. Altogether, these results suggest that E2F1 may also be involved in the inhibition of GNP proliferation during rat postnatal development despite its conventional mitogenic effects.

The long adventurous journey of rhombic lip cells in jawed vertebrates: a comparative developmental analysis

This review summarizes vertebrate rhombic lip and early cerebellar development covering classic approaches up to modern developmental genetics which identifies the relevant differential gene expression domains and their progeny. Most of this information is derived from amniotes. However, progress in anamniotes, particularly in the zebrafish, has recently been made. The current picture suggests that rhombic lip and cerebellar development in jawed vertebrates (gnathostomes) share many characteristics. Regarding cerebellar development, these include a ptf1a expressing ventral cerebellar proliferation (VCP) giving rise to Purkinje cells and other inhibitory cerebellar cell types, and an atoh1 expressing upper rhombic lip giving rise to an external granular layer (EGL, i.e., excitatory granule cells) and an early ventral migration into the anterior rhombencephalon (cholinergic nuclei). As for the lower rhombic lip (LRL), gnathostome commonalities likely include the formation of precerebellar nuclei (mossy fiber origins) and partially primary auditory nuclei (likely convergently evolved) from the atoh1 expressing dorsal zone. The fate of the ptf1a expressing ventral LRL zone which gives rise to (excitatory cells of) the inferior olive (climbing fiber origin) and (inhibitory cells of ) cochlear nuclei in amniotes, has not been determined in anamniotes. Special for the zebrafish in comparison to amniotes is the predominant origin of anamniote excitatory deep cerebellar nuclei homologs (i.e., eurydendroid cells) from ptf1a expressing VCP cells, the sequential activity of various atoh1 paralogs and the incomplete coverage of the subpial cerebellar plate with proliferative EGL cells. Nevertheless, the conclusion that a rhombic lip and its major derivatives evolved with gnathostome vertebrates only and are thus not an ancestral craniate character complex is supported by the absence of a cerebellum (and likely absence of its afferent and efferent nuclei) in jawless fishes