BM88 is an early marker of proliferating precursor cells that will differentiate into the neuronal lineage

Pan-Cancer Analysis and Experimental Validation of CEND1 as a Prognostic and Immune Infiltration-Associated Biomarker for Gliomas

Cell cycle exit and neuronal differentiation 1 (CEND1), highly expressed in the brain, is a specific transmembrane protein which plays a tumor suppressor role. This study is performed to investigate the role of CEND1 in various cancers through pan-cancer analysis, and further investigate its functions in gliomas by cell experiments. The expression and subcellular localization of CEND1 in different cancer types were analyzed utilizing the data from the GEPIA, UCSC, UALCAN and HPA databases. Relationships of CEND1 expression with prognosis, immunomodulation-related genes, immune checkpoint genes, microsatellite instability (MSI), tumor mutation burden (TMB) and RNA modifications were analyzed based on the TCGA database. The ESTIMATE algorithm was utilized to evaluate tumors' StromalScore, Immune Score, and ESTIMATES Score. The cBioPortal database was employed to analyze the categories and frequencies of CEND1 gene alterations. Biological functions and co-expression patterns of CEND1 in gliomas were explored using the LinkedOmics database, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses were conducted. The interactions between CEND1 and drugs were explored employing the Comparative Toxicogenomics Database and molecular docking technology. Cell experiments were conducted to analyze triptonide's effects on glioma cells through CCK-8, flow cytometry and qRT-PCR. CEND1 was lowly expressed in gliomas, and high CEND1 expression was correlated to better overall survival of glioma patients (HR = 0.65, P = 0.02). Deep deletion was the main type of hereditary change of CEND1 mutation. CEND1 expression was markedly associated with immune infiltration, TMB, MSI, and RNA modification in various tumors (r > 0.3, P < 0.05). CEND1 co-expressed genes in gliomas were markedly correlated with immune responses and cell cycle (FDR < 0.05). Triptonide could bind well to CEND1 (-5.0 kcal/mol), and triptonide could facilitate CEND1 expression in glioma cells and cell apoptosis, and block the cell cycle progression (P < 0.05). CEND1 serves as a potential biomarker for pan-cancer. Particularly in gliomas, CEND1 is a key regulator of cell apoptosis and cell cycle, and a potential target for glioma treatment.

Pan-retinal ganglion cell markers in mice, rats, and rhesus macaques

Univocal identification of retinal ganglion cells (RGCs) is an essential prerequisite for studying their degeneration and neuroprotection. Before the advent of phenotypic markers, RGCs were normally identified using retrograde tracing of retinorecipient areas. This is an invasive technique, and its use is precluded in higher mammals such as monkeys. In the past decade, several RGC markers have been described. Here, we reviewed and analyzed the specificity of nine markers used to identify all or most RGCs, i.e., pan-RGC markers, in rats, mice, and macaques. The best markers in the three species in terms of specificity, proportion of RGCs labeled, and indicators of viability were BRN3A, expressed by vision-forming RGCs, and RBPMS, expressed by vision- and non-vision-forming RGCs. NEUN, often used to identify RGCs, was expressed by non-RGCs in the ganglion cell layer, and therefore was not RGC-specific. γ-SYN, TUJ1, and NF-L labeled the RGC axons, which impaired the detection of their somas in the central retina but would be good for studying RGC morphology. In rats, TUJ1 and NF-L were also expressed by non-RGCs. BM88, ERRβ, and PGP9.5 are rarely used as markers, but they identified most RGCs in the rats and macaques and ERRβ in mice. However, PGP9.5 was also expressed by non-RGCs in rats and macaques and BM88 and ERRβ were not suitable markers of viability.

Alterations of serine racemase expression determine proliferation and differentiation of neuroblastoma cells

Although the role of serine racemase (SR) in neuropsychiatric disorders has been extensively studied, its role in cell proliferation and differentiation remains unclear. Deletion of Srr, the encoding gene for SR, has been shown to reduce dendritic arborization and dendritic spine density in the brains of adult mice, whereas increased SR levels have been associated with differentiation in cell cultures. Previously, we demonstrated that valproic acid induces differentiation in the N2A neuroblastoma cell line, and that this differentiation is associated with increased SR expression. These observations suggest that SR may have a role in cell proliferation and differentiation. We herein found that both valproic acid and all-trans retinoic acid induced N2A differentiation. In contrast, knockdown of SR reduced levels of differentiation, increased N2A proliferation, promoted cell cycle entry, and modulated expression of cell cycle-related proteins. To further evaluate the effects of SR expression on cell proliferation and differentiation, we used an in vivo model of neuroblastoma in nude mice. N2A cells stably expressing scramble shRNA (Srr^wt -N2A) or specific Srr shRNA (Srr^kd -N2A) were subcutaneously injected into nude mice. The weights and volumes of Srr^wt -N2A-derived tumors were lower than Srr^kd -N2A-derived tumors. Furthermore, Srr^wt -N2A-derived tumors were significantly mitigated by intraperitoneal injection of valproic acid, whereas Srr^kd -N2A-derived tumors were unaffected. Taken together, our findings demonstrate for the first time that alterations in SR expression determine the transition between proliferation and differentiation in neural progenitor cells. Thus, in addition to its well-established roles in neuropsychiatric disorders, our study has highlighted a novel role for SR in cell proliferation and differentiation.

Cell cycle exit and neuronal differentiation 1-engineered embryonic neural stem cells enhance neuronal differentiation and neurobehavioral recovery after experimental traumatic brain injury

Our previous study showed that cell cycle exit and neuronal differentiation 1 (CEND1) may participate in neural stem cell cycle exit and oriented differentiation. However, whether CEND1-transfected neural stem cells can improve the prognosis of traumatic brain injury remained unclear. In this study, we performed quantitative proteomic analysis and found that after traumatic brain injury, CEND1 expression was downregulated in mouse brain tissue. Three days after traumatic brain injury, we transplanted CEND1-transfected neural stem cells into the area surrounding the injury site. We found that at 5 weeks after traumatic brain injury, transplantation of CEND1-transfected neural stem cells markedly alleviated brain atrophy and greatly improved neurological function. In vivo and in vitro results indicate that CEND1 overexpression inhibited the proliferation of neural stem cells, but significantly promoted their neuronal differentiation. Additionally, CEND1 overexpression reduced protein levels of Notch1 and cyclin D1, but increased levels of p21 in CEND1-transfected neural stem cells. Treatment with CEND1-transfected neural stem cells was superior to similar treatment without CEND1 transfection. These findings suggest that transplantation of CEND1-transfected neural stem cells is a promising cell therapy for traumatic brain injury. This study was approved by the Animal Ethics Committee of the School of Biomedical Engineering of Shanghai Jiao Tong University, China (approval No. 2016034) on November 25, 2016.

Expression of Mammalian BM88/CEND1 in Drosophila Affects Nervous System Development by Interfering with Precursor Cell Formation

We used Drosophila melanogaster as an experimental model to express mouse and pig BM88/CEND1 (cell cycle exit and neuronal differentiation 1) in order to investigate its potential functional effects on Drosophila neurogenesis. BM88/CEND1 is a neuron-specific protein whose function is implicated in triggering cells to exit from the cell cycle and differentiate towards a neuronal phenotype. Transgenic flies expressing either mouse or pig BM88/CEND1 in the nervous system had severe neuronal phenotypes with variable expressivity at various stages of embryonic development. In early embryonic stage 10, BM88/CEND1 expression led to an increase in the neural-specific antigenicity of neuroectoderm at the expense of precursor cells [neuroblasts (Nbs) and ganglion mother cells (GMCs)] including the defective formation and differentiation of the MP2 precursors, whereas at later stages (12-15), protein accumulation induced gross morphological defects primarily in the CNS accompanied by a reduction of Nb and GMC markers. Furthermore, the neuronal precursor cells of embryos expressing BM88/CEND1 failed to carry out proper cell-cycle progression as revealed by the disorganized expression patterns of specific cell-cycle markers. BM88/CEND1 accumulation in the Drosophila eye affected normal eye disc development by disrupting the ommatidia. Finally, we demonstrated that expression of BM88/CEND1 modified/reduced the levels of activated MAP kinase indicating a functional effect of BM88/CEND1 on the MAPK signaling pathway. Our findings suggest that the expression of mammalian BM88/CEND1 in Drosophila exerts specific functional effects associated with neuronal precursor cell formation during embryonic neurogenesis and proper eye disc development. This study also validates the use of Drosophila as a powerful model system in which to investigate gene function and the underlying molecular mechanisms.

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.

Increased Anxiety-Related Behavior, Impaired Cognitive Function and Cellular Alterations in the Brain of Cend1-deficient Mice

Cend1 is a neuronal-lineage specific modulator involved in coordination of cell cycle exit and differentiation of neuronal precursors. We have previously shown that Cend1^-/- mice show altered cerebellar layering caused by increased proliferation of granule cell precursors, delayed radial granule cell migration and compromised Purkinje cell differentiation, leading to ataxic gait and deficits in motor coordination. To further characterize the effects of Cend1 genetic ablation we determined herein a range of behaviors, including anxiety and exploratory behavior in the elevated plus maze (EPM), associative learning in fear conditioning, and spatial learning and memory in the Morris water maze (MWM). We observed significant deficits in all tests, suggesting structural and/or functional alterations in brain regions such as the cortex, amygdala and the hippocampus. In agreement with these findings, immunohistochemistry revealed reduced numbers of γ amino butyric acid (GABA) GABAergic interneurons, but not of glutamatergic projection neurons, in the adult cerebral cortex. Reduced GABAergic interneurons were also observed in the amygdala, most notably in the basolateral nucleus. The paucity in GABAergic interneurons in adult Cend1^-/- mice correlated with increased proliferation and apoptosis as well as reduced migration of neuronal progenitors from the embryonic medial ganglionic eminence (MGE), the origin of these cells. Further we noted reduced GABAergic neurons and aberrant neurogenesis in the adult dentate gyrus (DG) of the hippocampus, which has been previously shown to confer spatial learning and memory deficits. Our data highlight the necessity of Cend1 expression in the formation of a structurally and functionally normal brain phenotype.

Estradiol and the Development of the Cerebral Cortex: An Unexpected Role?

The cerebral cortex undergoes rapid folding in an "inside-outside" manner during embryonic development resulting in the establishment of six discrete cortical layers. This unique cytoarchitecture occurs via the coordinated processes of neurogenesis and cell migration. In addition, these processes are fine-tuned by a number of extracellular cues, which exert their effects by regulating intracellular signaling pathways. Interestingly, multiple brain regions have been shown to develop in a sexually dimorphic manner. In many cases, estrogens have been demonstrated to play an integral role in mediating these sexual dimorphisms in both males and females. Indeed, 17β-estradiol, the main biologically active estrogen, plays a critical organizational role during early brain development and has been shown to be pivotal in the sexually dimorphic development and regulation of the neural circuitry underlying sex-typical and socio-aggressive behaviors in males and females. However, whether and how estrogens, and 17β-estradiol in particular, regulate the development of the cerebral cortex is less well understood. In this review, we outline the evidence that estrogens are not only present but are engaged and regulate molecular machinery required for the fine-tuning of processes central to the cortex. We discuss how estrogens are thought to regulate the function of key molecular players and signaling pathways involved in corticogenesis, and where possible, highlight if these processes are sexually dimorphic. Collectively, we hope this review highlights the need to consider how estrogens may influence the development of brain regions directly involved in the sex-typical and socio-aggressive behaviors as well as development of sexually dimorphic regions such as the cerebral cortex.

Adeno-Associated Viral Vectors Serotype 8 for Cell-Specific Delivery of Therapeutic Genes in the Central Nervous System

Adeno-associated viruses (AAVs) have become highly promising tools for research and clinical applications in the central nervous system (CNS). However, specific delivery of genes to the cell type of interest is essential for the success of gene therapy and therefore a correct selection of the promoter plays a very important role. Here, AAV8 vectors carrying enhanced green fluorescent protein (eGFP) as reporter gene under the transcriptional control of different CNS-specific promoters were used and compared with a strong ubiquitous promoter. Since one of the main limitations of AAV-mediated gene delivery lies in its restricted cloning capacity, we focused our work on small-sized promoters. We tested the transduction efficacy and specificity of each vector after stereotactic injection into the mouse striatum. Three glia-specific AAV vectors were generated using two truncated forms of the human promoter for glial fibrillar acidic protein (GFAP) as well as a truncated form of the murine GFAP promoter. All three vectors resulted in predominantly glial expression; however we also observed eGFP expression in other cell-types such as oligodendrocytes, but never in neurons. In addition, robust and neuron-specific eGFP expression was observed using the minimal promoters for the neural protein BM88 and the neuronal nicotinic receptor β2 (CHRNB2). In summary, we developed a set of AAV vectors designed for specific expression in cells of the CNS using minimal promoters to drive gene expression when the size of the therapeutic gene matters.

CEND1 and NEUROGENIN2 Reprogram Mouse Astrocytes and Embryonic Fibroblasts to Induced Neural Precursors and Differentiated Neurons

Recent studies demonstrate that astroglia from non-neurogenic brain regions can be reprogrammed into functional neurons through forced expression of neurogenic factors. Here we explored the effect of CEND1 and NEUROG2 on reprogramming of mouse cortical astrocytes and embryonic fibroblasts. Forced expression of CEND1, NEUROG2, or both resulted in acquisition of induced neuronal cells expressing subtype-specific markers, while long-term live-cell imaging highlighted the existence of two different modes of neuronal trans-differentiation. Of note, a subpopulation of CEND1 and NEUROG2 double-transduced astrocytes formed spheres exhibiting neural stem cell properties. mRNA and protein expression studies revealed a reciprocal feedback loop existing between the two molecules, while knockdown of endogenous CEND1 demonstrated that it is a key mediator of NEUROG2-driven neuronal reprogramming. Our data suggest that common reprogramming mechanisms exist driving the conversion of lineage-distant somatic cell types to neurons and reveal a critical role for CEND1 in NEUROG2-driven astrocytic reprogramming.

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CEND1 reprograms astrocytes and fibroblasts to GABAergic neurons

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Neurospheres are formed from CEND1⁺ and NEUROG2⁺ cells through the β-catenin pathway

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CEND1 and NEUROG2 participate in a reciprocal feedback loop leading to neurogenesis

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CEND1 is a key mediator of NEUROG2 reprogramming function

Functional Interactions between BM88/Cend1, Ran-binding protein M and Dyrk1B kinase affect cyclin D1 levels and cell cycle progression/exit in mouse neuroblastoma cells

BM88/Cend1 is a neuronal-lineage specific modulator with a pivotal role in coordination of cell cycle exit and differentiation of neuronal precursors. In the current study we identified the signal transduction scaffolding protein Ran-binding protein M (RanBPM) as a BM88/Cend1 binding partner and showed that BM88/Cend1, RanBPM and the dual specificity tyrosine-phosphorylation regulated kinase 1B (Dyrk1B) are expressed in mouse brain as well as in cultured embryonic cortical neurons while RanBPM can form complexes with either of the two other proteins. To elucidate a potential mechanism involving BM88/Cend1, RanBPM and Dyrk1B in cell cycle progression/exit, we transiently co-expressed these proteins in mouse neuroblastoma Neuro 2a cells. We found that the BM88/Cend1-dependent or Dyrk1B-dependent down-regulation of cyclin D1 is reversed following their functional interaction with RanBPM. More specifically, functional interaction of RanBPM with either BM88/Cend1 or Dyrk1B stabilizes cyclin D1 in the nucleus and promotes 5-bromo-2'-deoxyuridine (BrdU) incorporation as a measure of enhanced cell proliferation. However, the RanBPM-dependent Dyrk1B cytosolic retention and degradation is reverted in the presence of Cend1 resulting in cyclin D1 destabilization. Co-expression of RanBPM with either BM88/Cend1 or Dyrk1B also had a negative effect on Neuro 2a cell differentiation. Our results suggest that functional interactions between BM88/Cend1, RanBPM and Dyrk1B affect the balance between cellular proliferation and differentiation in Neuro 2a cells and indicate that a potentially similar mechanism may influence cell cycle progression/exit and differentiation of neuronal precursors.

Loss of Ahi1 affects early development by impairing BM88/Cend1-mediated neuronal differentiation

Mutations in the Abelson helper integration site-1 (AHI1) gene result in N-terminal Ahi1 fragments and cause Joubert syndrome, an autosomal recessive brain malformation disorder associated with delayed development. How AHI1 mutations lead to delayed development remains unclear. Here we report that full-length, but not N-terminal, Ahi1 binds Hap1, a huntingtin-associated protein that is essential for the postnatal survival of mice and that this binding is regulated during neuronal differentiation by nerve growth factor. Nerve growth factor induces dephosphorylation of Hap1A and decreases its association with Ahi1, correlating with increased Hap1A distribution in neurite tips. Consistently, Ahi1 associates with phosphorylated Hap1A in cytosolic, but not in synaptosomal, fractions isolated from mouse brain, suggesting that Ahi1 functions mainly in the soma of neurons. Mass spectrometry analysis of cytosolic Ahi1 immunoprecipitates reveals that Ahi1 also binds Cend1 (cell cycle exit and neuronal differentiation protein 1)/BM88, a neuronal protein that mediates neuronal differentiation and is highly expressed in postnatal mouse brain. Loss of Ahi1 reduces the levels of Cend1 in the hypothalamus of Ahi1 KO mice, which show retarded growth during postnatal days. Overexpressed Ahi1 can stabilize Cend1 in cultured cells. Furthermore, overexpression of Cend1 can rescue the neurite extension defects of hypothalamic neurons from Ahi1 KO mice. Our findings suggest that Cend1 is involved in Ahi1-associated hypothalamic neuronal differentiation in early development, giving us fresh insight into the mechanism behind the delayed development in Joubert syndrome.

[Length of cell cycle in neural development]

Neural development of mammals generates a series of morphological and functional alterations in neural precursors. The precursors change the length of cell cycle in the process. Importantly, the changes are related to cell fate determination. Cellular and environmental factors have been elucidated including cyclin complex, notch signal pathway, proneural gene target proteins, microtubule and motor proteins. In the cell-cycle length hypothesis, cell cycle length could influence the accumulation of cell fate determinants in precursors, which decides the final cell fate of daughter cells. This study summarizes recent advances in the field.

Impaired cerebellar development and deficits in motor coordination in mice lacking the neuronal protein BM88/Cend1

During nervous system development, neural progenitors arise in proliferative zones, then exit the cell cycle and differentiate as they migrate away from these zones. The neuronal protein BM88/Cend1 has been implicated in coordination of cell cycle exit and differentiation of neuronal precursors. To further elucidate its function we generated Cend1 knock-out mice and analyzed their phenotype during postnatal cerebellar development. Cend1(-/-) mice showed no overt abnormalities in the gross anatomy of the cerebellum or other brain regions. However, detailed analysis revealed alterations in cerebellar layering arising from increased proliferation of granule cell precursors, delayed radial granule cell migration and impaired Purkinje cell differentiation. Accordingly, expression of Patched1, cyclin D1, reelin and brain-derived neurotrophic factor, which correlate with morphological development of the cerebellum, was altered in Cend1(-/-) mice. The observed anatomical and molecular alterations were accompanied by deficits in motor behaviour. Our results suggest that Cend1 is required for normal cerebellar development.

Transplantation of embryonic neural stem/precursor cells overexpressing BM88/Cend1 enhances the generation of neuronal cells in the injured mouse cortex

The intrinsic inability of the central nervous system to efficiently repair traumatic injuries renders transplantation of neural stem/precursor cells (NPCs) a promising approach towards repair of brain lesions. In this study, NPCs derived from embryonic day 14.5 mouse cortex were genetically modified via transduction with a lentiviral vector to overexpress the neuronal lineage-specific regulator BM88/Cend1 that coordinates cell cycle exit and differentiation of neuronal precursors. BM88/Cend1-overexpressing NPCs exhibiting enhanced differentiation into neurons in vitro were transplanted in a mouse model of acute cortical injury and analyzed in comparison with control NPCs. Immunohistochemical analysis revealed that a smaller proportion of BM88/Cend1-overexpressing NPCs, as compared with control NPCs, expressed the neural stem cell marker nestin 1 day after transplantation, while the percentage of nestin-positive cells was significantly reduced thereafter in both types of cells, being almost extinct 1 week post-grafting. Both types of cells did not proliferate up to 4 weeks in vivo, thus minimizing the risk of tumorigenesis. In comparison with control NPCs, Cend1-overexpressing NPCs generated more neurons and less glial cells 1 month after transplantation in the lesioned cortex whereas the majority of graft-derived neurons were identified as GABAergic interneurons. Furthermore, transplantation of Cend1-overexpressing NPCs resulted in a marked reduction of astrogliosis around the lesioned area as compared to grafts of control NPCs. Our results suggest that transplantation of Cend1-overexpressing NPCs exerts beneficial effects on tissue regeneration by enhancing the number of generated neurons and restricting the formation of astroglial scar, in a mouse model of cortical brain injury.

C38, equivalent to BM88, is developmentally expressed in maturing retinal neurons and enhances neuronal maturation

C38 antigen is specifically expressed in neuronal cells of the retina. The purpose of this study was to isolate C38 cDNA and determine its molecular functions. Sequence analysis of C38 cDNA revealed that C38 is equivalent to rat BM88, which has been reported to induce cell-cycle arrest and neuronal differentiation in Neuro2a cells. C38 and Ki67, a marker of proliferating cells, were not colocalized during retinal development. C38 was first detected in the retinal ganglion cells at embryonic day 16, much later than the expression of doublecortin, a marker of immature neurons. Although all the horizontal cells were post-mitotic at this stage, C38 was not detected in horizontal cells until the postnatal period. In addition, C38 over-expression did not induce neuronal differentiation or cell-cycle arrest of pluripotent P19 embryonal carcinoma cells. Instead, C38 promoted maturation during neuronal differentiation of P19 embryonal carcinoma cells by down-regulating Oct-3, a pluripotent cell marker and enhancing the expressions of positive regulators of neurogenesis. In conclusion, during retinal development, C38 is first expressed in post-mitotic retinal neurons and is up-regulated during their maturation. C38 does not induce neuronal competence in pluripotent cells, but does promote maturation in already committed neuronal cells.

BM88/Cend1 regulates stimuli-induced intracellular calcium mobilization

In neurogenesis, little is known about signal transduction pathways upstream of gene expression however, mounting evidence suggests that calcium release from internal stores plays a critical role. We have previously demonstrated that BM88 is a neuronal lineage-specific regulator of cell cycle exit and differentiation; we now report a link between BM88 and calcium signaling. Calcium imaging experiments revealed that P2Y-induced calcium mobilization is diminished in mouse neuroblastoma Neuro 2a cells stably transfected with BM88 (N2A-BM88 cells) as compared with N2A cells or N2A cells differentiated with retinoic acid. This effect is not restricted to N2A cells but is also observed in HeLa cells that are transiently transfected with BM88, indicating that cells of both neural and non-neural origin respond similarly. Further, activation of P2Y1 but not purinergic P2X receptors induces proliferation of N2A and to a lesser extent of N2A-BM88 cells. Conversely, knockdown of BM88 facilitates N2A cell proliferation both under stimulating and non-stimulating conditions. Importantly, N2A-BM88 cells are less susceptible to apoptosis triggered by C2-ceramide and exhibit reduced C2-ceramide-induced intracellular calcium release. Higher calcium uptake from mitochondria and/or lower calcium levels inside the endoplasmic reticulum may explain the reduced calcium mobilization in response to BM88. Overall, our data reveal a novel signaling mechanism by which BM88 interferes with calcium release from inositol 1,4,5-trisphosphate-sensitive stores and exerts anti-proliferative and anti-apoptotic functions.

BM88/Cend1 expression levels are critical for proliferation and differentiation of subventricular zone-derived neural precursor cells

Neural stem cells remain in two areas of the adult mammalian brain, the subventricular zone (SVZ) and the dentate gyrus of the hippocampus. Ongoing neurogenesis via the SVZ-rostral migratory stream pathway maintains neuronal replacement in the olfactory bulb (OB) throughout life. The mechanisms determining how neurogenesis is restricted to only a few regions in the adult, in contrast to its more widespread location during embryogenesis, largely depend on controlling the balance between precursor cell proliferation and differentiation. BM88/Cend1 is a neuronal lineage-specific regulator implicated in cell cycle exit and differentiation of precursor cells in the embryonic neural tube. Here we investigated its role in postnatal neurogenesis. Study of in vivo BM88/Cend1 distribution revealed that it is expressed in low levels in neuronal precursors of the adult SVZ and in high levels in postmitotic OB interneurons. To assess the functional significance of BM88/Cend1 in neuronal lineage progression postnatally, we challenged its expression levels by gain- and loss-of-function approaches using lentiviral gene transfer in SVZ-derived neurospheres. We found that BM88/Cend1 overexpression decreases proliferation and favors neuronal differentiation, whereas its downregulation using new-generation RNA interference vectors yields an opposite phenotype. Our results demonstrate that BM88/Cend1 participates in cell cycle control and neuronal differentiation mechanisms during neonatal SVZ neurogenesis and becomes crucial for the transition from neuroblasts to mature neurons when reaching high levels.

Lengthening the G(1) phase of neural progenitor cells is concurrent with an increase of symmetric neuron generating division after stroke

The proportion of neural progenitors that remain in (P fraction) and exit from (Q fraction) the cell cycle determines the degree of neurogenesis. Using S-phase labeling with 5-bromo-2'-deoxyuridine and a double nucleoside analog-labeling scheme, we measured the cell-cycle kinetics of neural progenitors and estimated the proportion of P and Q fractions in the subventricular zone (SVZ) of adult rats subjected to stroke. Stroke increased SVZ cell proliferation, starting 2 days, reaching a maximum 4 and 7 days after stroke. The cell-cycle length (T(C)) of SVZ cells changed dynamically over a period of 2 to 14 days after stroke, with the shortest length of 11 h at 2 days after stroke. The reduction of the T(C) resulted from a decrease of the G(1) phase because the G(2), M, and S phases were unchanged. In addition, during this period, reduction of the G(1) phase was concomitant with an increase in the P fraction, whereas an augmentation of the Q fraction was associated with lengthening of the G(1) phase. Furthermore, approximately 90% of cells that exited the cell cycle were neurons and the population of a pair of dividing daughter cells with a neuronal marker increased from 9% at 2 days to 26% at 14 days after stroke. These data suggest that stroke triggers early expansion of the progenitor pool via shortening the cell-cycle length and retaining daughter cells within the cell cycle, and the lengthening of G(1) leads to daughter cells exiting the cell cycle and differentiating into neurons.

Epigenetic regulation of kappa opioid receptor gene in neuronal differentiation

The gene of mouse kappa opioid receptor (KOR) utilizes two promoters, P1 and P2. P1 is active in various brain areas and constitutively in P19 mouse embryonal carcinoma cells. P2 is active in limited brain stem areas of adult animals and only in late differentiated cells of P19 induced for neuronal differentiation in the presence of nerve growth factor (NGF). NGF response of P2 was found to be mediated by a specific binding site for transcription factor activation protein 2 (AP2) located in P2. Electrophoretic gel shift assay showed specific binding of this AP2 site by AP2beta, but not AP2alpha. Knockdown of endogenous AP2beta with siRNA abolished the stimulating effect of NGF on the expression of transcripts driven by P2. Binding of endogenous AP2beta on the endogenous KOR P2 chromatin region was also confirmed by chromatin immunoprecipitation. The effect of NGF was inhibited by LY2942002 (phosphatidylinositol 3-kinase, PI3K inhibitor), suggesting that PI3K was involved in signaling pathway mediating the effect of NGF stimulation on KOR P2. The chromatin of P2 in P19 was found to be specifically modified following NGF stimulation, which included demethylation at Lys9 and dimethylation at Lys4 of histone H3 and was consistent with the increased recruitment of RNA polymerase II to this promoter. This study presents the first evidence for epigenetic changes occurred on a specific KOR promoter triggered by NGF in cells undergoing neuronal differentiation. This epigenetic change is mediated by recruited AP2beta to this promoter and involves the PI3K system.

BM88/Cend1 is involved in histone deacetylase inhibition-mediated growth arrest and differentiation of neuroblastoma cells

Histone deacetylase inhibitors arrest the growth of neuroblastoma cells and induce differentiation. Identification of target genes that co-ordinate and mediate these effects is important for understanding the function of this novel class of antitumour drugs. We report here that trichostatin-A (TSA) specifically induces the transcription of Cend1, a neuronal-lineage specific regulator of cell cycle exit and differentiation, in neuroblastoma Neuro2A cells, but not in non-neuronal cells. Furthermore, we show that knockdown of Cend1 alleviates both the anti-proliferative and differentiation effect of TSA. Our findings suggest that Cend1 is an important molecular target for HDAC inhibition.

BM88/CEND1 coordinates cell cycle exit and differentiation of neuronal precursors

During development, coordinate regulation of cell cycle exit and differentiation of neuronal precursors is essential for generation of appropriate number of neurons and proper wiring of neuronal circuits. BM88 is a neuronal protein associated in vivo with terminal neuron-generating divisions, marking the exit of proliferative cells from the cell cycle. Here, we provide functional evidence that BM88 is sufficient to initiate the differentiation of spinal cord neural precursors toward acquisition of generic neuronal and subtype-specific traits. Gain-of-function approaches show that BM88 negatively regulates proliferation of neuronal precursors, driving them to prematurely exit the cell cycle, down-regulate Notch1, and commit to a neuronal differentiation pathway. The combined effect on proliferation and differentiation results in precocious induction of neurogenesis and generation of postmitotic neurons within the ventricular zone. The dual action of BM88 is not recapitulated by the cell cycle inhibitor p27Kip1, suggesting that cell cycle exit does not induce differentiation by default. Mechanistically, induction of endogenous BM88 by forced expression of the proneural gene Mash1 indicates that BM88 is part of the differentiation program activated by proneural genes. Furthermore, BM88 gene silencing conferred by small interfering RNA in spinal cord neural progenitor cells enhances cell cycle progression and impairs neuronal differentiation. Our results implicate BM88 in the synchronization of cell cycle exit and differentiation of neuronal precursors in the developing nervous system.

Cell-cycle control and cortical development

The spatio-temporal timing of the last round of mitosis, followed by the migration of neuroblasts to the cortical plate leads to the formation of the six-layered cortex that is subdivided into functionally defined cortical areas. Whereas many of the cellular and molecular mechanisms have been established in rodents, there are a number of unique features that require further elucidation in primates. Recent findings both in rodents and in primates indicate that regulation of the cell cycle, specifically of the G1 phase has a crucial role in controlling area-specific rates of neuron production and the generation of cytoarchitectonic maps.

The Retinoblastoma family member p107 regulates the rate of progenitor commitment to a neuronal fate

The Retinoblastoma protein p107 regulates the neural precursor pool in both the developing and adult brain. As p107-deficient mice exhibit enhanced levels of Hes1, we questioned whether p107 regulates neural precursor self-renewal through the repression of Hes1. p107 represses transcription at the Hes1 promoter. Despite an expanded neural precursor population, p107-null mice exhibit a striking reduction in the number of cortical neurons. Hes1 deficiency rescues neurosphere numbers in p107-null embryos. We find that the loss of a single Hes1 allele in vivo restores the number of neural precursor cells at the ventricular zone. Neuronal birthdating analysis reveals a dramatic reduction in the rate of neurogenesis, demonstrating impairment in p107(-/-) progenitors to commit to a neuronal fate. The loss of a single Hes1 allele restores the number of newly generated neurons in p107-deficient brains. Together, we identify a novel function for p107 in promoting neural progenitor commitment to a neuronal fate.

BM88 is a dual function molecule inducing cell cycle exit and neuronal differentiation of neuroblastoma cells via cyclin D1 down-regulation and retinoblastoma protein hypophosphorylation

Control of cell cycle progression/exit and differentiation of neuronal precursors is of paramount importance during brain development. BM88 is a neuronal protein associated with terminal neuron-generating divisions in vivo and is implicated in mechanisms underlying neuronal differentiation. Here we have used mouse neuroblastoma Neuro 2a cells as an in vitro model of neuronal differentiation to dissect the functional properties of BM88 by implementing gain- and loss-of-function approaches. We demonstrate that stably transfected cells overexpressing BM88 acquire a neuronal phenotype in the absence of external stimuli, as judged by enhanced expression of neuronal markers and neurite outgrowth-inducing signaling molecules. In addition, cell cycle measurements involving cell growth assays, BrdUrd incorporation, and fluorescence-activated cell sorting analysis revealed that the BM88-transfected cells have a prolonged G(1) phase, most probably corresponding to cell cycle exit at the G(0) restriction point, as compared with controls. BM88 overexpression also results in increased levels of the cell cycle regulatory protein p53, and accumulation of the hypophosphorylated form of the retinoblastoma protein leading to cell cycle arrest, with concomitant decreased levels and, in many cells, cytoplasmic localization of cyclin D1. Conversely, BM88 gene silencing using RNA interference experiments resulted in acceleration of cell proliferation accompanied by impairment of retinoic acid-induced neuronal differentiation of Neuro 2a cells. Taken together, our results suggest that BM88 plays an essential role in regulating cell cycle exit and differentiation of Neuro 2a cells toward a neuronal phenotype and further support its involvement in the proliferation/differentiation transition of neural stem/progenitor cells during embryonic development.

Expression pattern of BM88 in the developing nervous system of the chick and mouse embryo

We isolated a chick homologue of BM88 (cBM88), a cell-intrinsic nervous system-specific protein and examined the expression of BM88 mRNA and protein in the developing brain, spinal cord and peripheral nervous system of the chick embryo by in situ hybridization and immunohistochemistry. cBM88 is widely expressed in the developing central nervous system, both in the ventricular and mantle zones where precursor and differentiated cells lie, respectively. In the spinal cord, particularly strong cBM88 expression is detected ventrally in the motor neuron area. cBM88 is also expressed in the dorsal root ganglia and sympathetic ganglia. In the early neural tube, cBM88 is first detected at HH stage 15 and its expression increases with embryonic age. At early stages, cBM88 expression is weaker in the ventricular zone (VZ) and higher in the mantle zone. At later stages, when gliogenesis persists instead of neurogenesis, BM88 expression is abolished in the VZ and cBM88 is restricted in the neuron-containing mantle zone of the neural tube. Association of cBM88 expression with cells of the neuronal lineage in the chick spinal cord was demonstrated using a combination of markers characteristic of neuronal or glial precursors, as well as markers of differentiated neuronal, oligodendroglial and astroglial cells. In addition to the spinal cord, cBM88 is expressed in the HH stage 45 (embryonic day 19) brain, including the telencephalon, diencephalon, mesencephalon, optic tectum and cerebellum. BM88 is also widely expressed in the mouse embryonic CNS and PNS, in both nestin-positive neuroepithelial cells and post-mitotic betaIII-tubulin positive neurons.

Characterization of the BM88 promoter and identification of an 88 bp fragment sufficient to drive neurone-specific expression

BM88 is a neurone-specific protein implicated in cell cycle exit and differentiation of neuronal precursors. It is widely expressed in terminally differentiated neurones but also in neuronal progenitors, albeit in lower levels. Thus BM88 expression shows a tight correlation with the progression of progenitor cells towards neuronal differentiation. Here we report the genomic organization and proximal promoter characterization of the human and mouse BM88 genes. Both promoters lie in a CpG island, are TATA-less and have multiple transcription start sites. Deletion analysis performed on the human BM88 gene revealed an 88 bp minimal promoter fragment that is preferentially active in neural cells. Importantly, this minimal promoter is sufficient to confer specific transcriptional activity in primary neurones, but not in glial cells. Within the promoter region there are four functional Sp1-binding sites. Simultaneous mutations to all four Sp1 sites results in complete loss of promoter activity. Transactivation experiments revealed that Sp1 directly activates the BM88 promoter while activation also occurs in the presence of neurogenin-1. Characterization of the promoter elements that control neurone-specific and developmental expression of BM88 should contribute to the elucidation of the transcriptional networks that regulate the transition from a proliferative neural progenitor to a post-mitotic neurone.

Climbing Fiber Innervation of NG2-Expressing Glia in the Mammalian Cerebellum

The molecular layer of the cerebellar cortex is populated by glial progenitors that express ionotropic glutamate receptors and extend numerous processes among Purkinje cell dendrites. Here, we show that release of glutamate from climbing fiber (CF) axons produces AMPA receptor currents with rapid kinetics in these NG2-immunoreactive glial cells (NG2+ cells) in cerebellar slices. NG2+ cells may receive up to 70 discrete inputs from one CF and, unlike mature Purkinje cells, are often innervated by multiple CFs. Paired Purkinje cell-NG2+ cell recordings show that one CF can innervate both cell types. CF boutons make direct synaptic junctions with NG2+ cell processes, indicating that this rapid neuron-glia signaling occurs at discrete sites rather than through ectopic release at CF-Purkinje cell synapses. This robust activation of Ca2+-permeable AMPA receptors in NG2+ cells expands the influence of the olivocerebellar projection to this abundant class of glial progenitors.