The Nuclear Receptor TLX Is Required for Gliomagenesis within the Adult Neurogenic Niche

Neural stem cells (NSCs) continually generate functional neurons in the adult brain. Due to their ability to proliferate, deregulated NSCs or their progenitors have been proposed as the cells of origin for a number of primary central nervous system neoplasms, including infiltrating gliomas. The orphan nuclear receptor TLX is required for proliferation of adult NSCs, and its upregulation promotes brain tumor formation. However, it is unknown whether TLX is required for gliomagenesis. We examined the genetic interactions between TLX and several tumor suppressors, as well as the role of TLX-dependent NSCs during gliomagenesis, using mouse models. Here, we show that TLX is essential for the proliferation of adult NSCs with a single deletion of p21, p53, or Pten or combined deletion of Pten and p53. While brain tumors still form in Tlx mutant mice, these tumors are less infiltrative and rarely associate with the adult neurogenic niches, suggesting a non-stem-cell origin. Taken together, these results indicate a critical role for TLX in NSC-dependent gliomagenesis and implicate TLX as a therapeutic target to inhibit the development of NSC-derived brain tumors.     

Identification,characterization, and functional investigation of circular RNAs in subventricular zone of adult rat brain

Adult neural stem cells (NSCs) are able to self-renew and generate new neural cells. Identifying regulators of NSCs is significant for the development of NSC-based therapies for neurodegenerative diseases and brain injuries. Recently, circular RNAs (circRNAs) have been characterized in various cell lines and brain tissues, and found to participate in multiple biological processes. However, the expression pattern of circRNAs in adult NSCs is still unknown. Here, the subventricular zone (SVZ) of the lateral ventricle was isolated as the niche of NSCs in adult rat brain for RNA sequencing and the characteristics of circRNAs profiling in both SVZ and cerebral cortex were also investigated. As a result, 29 049 and 31 975 circRNAs were identified in SVZ and cortex, respectively. Among them, 41 were SVZ-specific and 48 were cortex-specific. 467 circRNAs were also found to express predominately in SVZ, while the cortex had other 423 circRNAs. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses revealed that the SVZ-specific circRNAs have close relationship with the regulation of NSC expansion and NSC-niche interaction, while the other differentially expressed circRNAs might be involved in neural cellular construction and nerve system function. Furthermore, the interactions between circRNAs and microRNAs were also explored, and the result showed that one SVZ-specific circRNA was capable to competitively bind miR-138-5p as a potential derepressive regulator in NSCs proliferation. Hence, our work has laid the foundations to decipher regulation mechanisms of circRNAs in adult NSCs and to develop circRNAs as novel biomarkers for adult NSCs.     

Copine1 regulates neural stem cell functions during brain development

Copine 1 (CPNE1) is a well-known phospholipid binding protein in plasma membrane of various cell types. In brain cells, CPNE1 is closely associated with AKT signaling pathway, which is important for neural stem cell (NSC) functions during brain development. Here, we investigated the role of CPNE1 in the regulation of brain NSC functions during brain development and determined its underlying mechanism. In this study, abundant expression of CPNE1 was observed in neural lineage cells including NSCs and immature neurons in human. With mouse brain tissues in various developmental stages, we found that CPNE1 expression was higher at early embryonic stages compared to postnatal and adult stages. To model developing brain in vitro, we used primary NSCs derived from mouse embryonic hippocampus. Our in vitro study shows decreased proliferation and multi-lineage differentiation potential in CPNE1 deficient NSCs. Finally, we found that the deficiency of CPNE1 downregulated mTOR signaling in embryonic NSCs. These data demonstrate that CPNE1 plays a key role in the regulation of NSC functions through the activation of AKT-mTOR signaling pathway during brain development.     

Jagged1 signals in the postnatal subventricular zone are required for neural stem cell self-renewal

Neural stem cells (NSCs) in the postnatal mammalian brain self-renew and are a source of neurons and glia. To date, little is known about the molecular and cellular mechanisms regulating the maintenance and differentiation of these multipotent progenitors. We show that Jagged1 is required by mitotic cells in the subventricular zone (SVZ) and stimulates self-renewal of multipotent epidermal growth factor-dependent NSCs. Jagged1-expressing cells line the adult SVZ and are juxtaposed to Notch1-expressing cells, some of which are putative NSCs. In vitro, endogenous Jagged1 acts through Notch1 to promote NSC maintenance and multipotency. In vivo, reducing Jagged1/Notch1 signaling decreases the number of proliferating cells in the SVZ. In addition, soluble Jagged1 promotes self-renewal and neurogenic potential of multipotent neural progenitors in vitro. Our findings suggest a central role for Jagged1 in the NSC niche in the SVZ for maintaining a population of NSCs in the postnatal brain.     

Role of the nuclear receptor Tailless in adult neural stem cells

Tailless (Tlx) is an orphan nuclear receptor which is specifically expressed in the neural stem cells of the two largest germinal neurogenesis zones in the adult mouse brain, the subventricular zone (SVZ) of the lateral ventricle and the subgranular zone (SGZ) of the dentate gyrus. By interacting with its cofactors, Tlx represses its target genes and plays an important role in the maintenance of adult NSCs. This review provides a snapshot of current knowledge about Tlx function in adult NSCs.     

Oct4-induced reprogramming is required for adult brain neural stem cell differentiation into midbrain dopaminergic neurons

Neural stem cells (NSCs) lose their competency to generate region-specific neuronal populations at an early stage during embryonic brain development. Here we investigated whether epigenetic modifications can reverse the regional restriction of mouse adult brain subventricular zone (SVZ) NSCs. Using a variety of chemicals that interfere with DNA methylation and histone acetylation, we showed that such epigenetic modifications increased neuronal differentiation but did not enable specific regional patterning, such as midbrain dopaminergic (DA) neuron generation. Only after Oct-4 overexpression did adult NSCs acquire a pluripotent state that allowed differentiation into midbrain DA neurons. DA neurons derived from Oct4-reprogrammed NSCs improved behavioural motor deficits in a rat model of Parkinson's disease (PD) upon intrastriatal transplantation. Here we report for the first time the successful differentiation of SVZ adult NSCs into functional region-specific midbrain DA neurons, by means of Oct-4 induced pluripotency.     

BCL2L11/BIM

In response to toxic stimuli, BCL2L11 (also known as BIM), a BH3-only protein, is released from its interaction with dynein light chain 1 (DYNLL1 also known as LC8) and can induce apoptosis by inactivating anti-apoptotic BCL2 proteins and by activating BAX-BAK1. Recently, we discovered that BCL2L11 interacts with BECN1 (Beclin 1), and that this interaction is facilitated by DYNLL1. BCL2L11 recruits BECN1 to microtubules by bridging BECN1 and DYNLL1, thereby inhibiting autophagy. In starvation conditions, BCL2L11 is phosphorylated by MAPK8/JNK and this phosphorylation abolishes the BCL2L11-DYNLL1 interaction, allowing dissociation of BCL2L11 and BECN1, thereby ameliorating autophagy inhibition. This finding demonstrates a novel function of BIM beyond its roles in apoptosis, highlighting the crosstalk between autophagy and apoptosis, and suggests that BCL2L11’s dual effects in inhibiting autophagy and promoting apoptosis may have important roles in disease pathogenesis.     

Adult neural stem cells bridge their niche

Major developments in the neural stem cell (NSC) field in recent years provide new insights into the nature of the NSC niche. In this perspective, we integrate recent anatomical data on the organization of the two main neurogenic niches in the adult brain, the ventricular-subventricular zone (V-SVZ) and the subgranular zone (SGZ), with signaling pathways that control the behavior of NSCs. NSCs in the adult brain stretch into physiologically distinct compartments of their niche. We propose how adult NSCs' morphology may allow these cells to integrate multiple signaling pathways arising from unique locations of their niche.     

Persistent sonic hedgehog signaling in adult brain determines neural stem cell positional identity

Neural stem cells (NSCs) persist in the subventricular zone (SVZ) of the adult brain. Location within this germinal region determines the type of neuronal progeny NSCs generate, but the mechanism of adult NSC positional specification remains unknown. We show that sonic hedgehog (Shh) signaling, resulting in high gli1 levels, occurs in the ventral SVZ and is associated with the genesis of specific neuronal progeny. Shh is selectively produced by a small group of ventral forebrain neurons. Ablation of Shh decreases production of ventrally derived neuron types, while ectopic activation of this pathway in dorsal NSCs respecifies their progeny to deep granule interneurons and calbindin-positive periglomerular cells. These results show that Shh is necessary and sufficient for the specification of adult ventral NSCs.     

Neural stem cells confer unique pinwheel architecture to the ventricular surface in neurogenic regions of the adult brain

Neural stem cells (NSCs, B1 cells) are retained in the walls of the adult lateral ventricles but, unlike embryonic NSCs, are displaced from the ventricular zone (VZ) into the subventricular zone (SVZ) by ependymal cells. Apical and basal compartments, which in embryonic NSCs play essential roles in self-renewal and differentiation, are not evident in adult NSCs. Here we show that SVZ B1 cells in adult mice extend a minute apical ending to directly contact the ventricle and a long basal process ending on blood vessels. A closer look at the ventricular surface reveals a striking pinwheel organization specific to regions of adult neurogenesis. The pinwheel's core contains the apical endings of B1 cells and in its periphery two types of ependymal cells: multiciliated (E1) and a type (E2) characterized by only two cilia and extraordinarily complex basal bodies. These results reveal that adult NSCs retain fundamental epithelial properties, including apical and basal compartmentalization, significantly reshaping our understanding of this adult neurogenic niche.     

Effects of Amyloid β-Peptides and Gangliosides on Mouse Neural Stem Cells

The interaction of amyloid β-proteins (Aβs) with membrane lipids has been postulated as an early event in Aβ fibril formation in Alzheimer’s disease. We evaluated the effects of several putative bioactive Aβs and gangliosides on neural stem cells (NSCs) isolated from embryonic mouse brains or the subventricular zone of adult mouse brains. Incubation of the isolated NSCs with soluble Aβ1–40 alone did not cause any change in the number of NSCs, but soluble Aβ1–42 increased their number. Aggregated Aβ1–40 and Aβ1–42 increased the number of NSCs but soluble and aggregated Aβ25–35 decreased the number. Soluble Aβ1–40 and Aβ1–42 did not affect the number of apoptotic cells but aggregated Aβ1–40 and Aβ1–42 did. When NSCs were treated with a combination of GM1 or GD3 and soluble Aβ1–42, cell proliferation was enhanced, indicating that both GM1 and GD3 as well as Aβs are involved in promoting cell proliferation and survival of NSCs. These observations suggest the potential of beneficial effects of using gangliosides and Aβs for promoting NSC proliferation.     

Characterization of TLX Expression in Neural Stem Cells and Progenitor Cells in Adult Brains

TLX has been shown to play an important role in regulating the self-renewal and proliferation of neural stem cells in adult brains. However, the cellular distribution of endogenous TLX protein in adult brains remains to be elucidated. In this study, we used immunostaining with a TLX-specific antibody to show that TLX is expressed in both neural stem cells and transit-amplifying neural progenitor cells in the subventricular zone (SVZ) of adult mouse brains. Then, using a double thymidine analog labeling approach, we showed that almost all of the self-renewing neural stem cells expressed TLX. Interestingly, most of the TLX-positive cells in the SVZ represented the thymidine analog-negative, relatively quiescent neural stem cell population. Using cell type markers and short-term BrdU labeling, we demonstrated that TLX was also expressed in the Mash1+ rapidly dividing type C cells. Furthermore, loss of TLX expression dramatically reduced BrdU label-retaining neural stem cells and the actively dividing neural progenitor cells in the SVZ, but substantially increased GFAP staining and extended GFAP processes. These results suggest that TLX is essential to maintain the self-renewing neural stem cells in the SVZ and that the GFAP+ cells in the SVZ lose neural stem cell property upon loss of TLX expression.Understanding the cellular distribution of TLX and its function in specific cell types may provide insights into the development of therapeutic tools for neurodegenerative diseases by targeting TLX in neural stem/progenitors cells.     

The neural stem cell fate determinant TLX promotes tumorigenesis and genesis of cells resembling glioma stem cells

A growing body of evidence indicates that deregulation of stem cell fate determinants is a hallmark of many types of malignancies. The neural stem cell fate determinant TLX plays a pivotal role in neurogenesis in the adult brain by maintaining neural stem cells. Here, we report a tumorigenic role of TLX in brain tumor initiation and progression. Increased TLX expression was observed in a number of glioma cells and glioma stem cells, and correlated with poor survival of patients with gliomas. Ectopic expression of TLX in the U87MG glioma cell line and Ink4a/Arf-deficient mouse astrocytes (Ink4a/Arf^-/- astrocytes) induced cell proliferation with a concomitant increase in cyclin D expression, and accelerated foci formation in soft agar and tumor formation in in vivo transplantation assays. Furthermore, overexpression of TLX in Ink4a/Arf^-/- astrocytes inhibited cell migration and invasion and promoted neurosphere formation and Nestin expression, which are hallmark characteristics of glioma stem cells, under stem cell culture conditions. Our results indicate that TLX is involved in glioma stem cell genesis and represents a potential therapeutic target for this type of malignancy.     

Prospective isolation of adult neural stem cells from the mouse subependymal zone

Neural stem cells (NSCs) have the remarkable capacity to self-renew and the lifelong ability to generate neurons in the adult mammalian brain. However, the molecular and cellular mechanisms contributing to these behaviors are still not understood. Now that prospective isolation of the NSCs has become feasible, these mechanisms can be studied. Here we describe a protocol for the efficient isolation of adult NSCs, by the application of a dual-labeling strategy on the basis of their glial identity and ciliated nature. The cells are isolated from the lateral ventricular subependymal zone (SEZ) of adult hGFAP-eGFP (human glial fibrillary acidic protein-enhanced green fluorescent protein) transgenic mice by fluorescence-activated cell sorting. Staining against prominin1 (CD133) allows the isolation of the NSCs (hGFAP-eGFP(+)/prominin1(+)), which can be further subdivided by labeling with the fluorescent epidermal growth factor. This protocol, which can be completed in 7 h, allows the assessment of quantitative changes in SEZ NSCs and the examination of their molecular and functional characteristics.     

Developmental cues and persistent neurogenic potential within an <Emphasis Type="Italic">in vitro</Emphasis> neural niche

Background  

Neurogenesis, the production of neural cell-types from neural stem cells (NSCs), occurs during development as well as within select regions of the adult brain. NSCs in the adult subependymal zone (SEZ) exist in a well-categorized niche microenvironment established by surrounding cells and their molecular products. The components of this niche maintain the NSCs and their definitive properties, including the ability to self-renew and multipotency (neuronal and glial differentiation).