Depletion of transit amplifying cells in the adult brain does not affect quiescent neural stem cell pool size

Neural stem cells (NSCs) are maintained in the adult mammalian brain throughout the animal's lifespan. NSCs in the subependymal zone infrequently divide and generate transit amplifying cells, which are destined to become olfactory bulb neurons. When transit amplifying cells are depleted, they are replenished by the quiescent NSC pool. However, the cellular basis for this recovery process remains largely unknown. In this study, we traced NSCs and their progeny after transit amplifying cells were eliminated by intraventricular infusion of cytosine β-D-arabinofuranoside. We found that although the number of neurosphere-forming NSCs decreased shortly after the treatment, they were restored to normal levels 3 weeks after the cessation of treatment. More importantly, the depletion of transit amplifying cells did not induce a significant expansion of the NSC pool by symmetric divisions. Our data suggest that the size of the NSC pool is hardly affected by brain damage due to antimitotic drug treatment.

Fut9 Deficiency Causes Abnormal Neural Development in the Mouse Cerebral Cortex and Retina

α1,3-Fucosyltransferase 9 (Fut9) is responsible for the synthesis of Lewis X [Le^X, Galβ1-4(Fucα1-3)GlcNAc] carbohydrate epitope, a marker for pluripotent or multipotent tissue-specific stem cells. Although Fut9-deficient mice show anxiety-related behaviors, structural and cellular abnormalities in the brain remain to be investigated. In this study, using in situ hybridization and immunohistochemical techniques in combination, we clarified the spatiotemporal expression of Fut9, together with Le^X, in the brain and retina. We found that Fut9-expressing cells are positive for Ctip2, a marker of neurons residing in layer V/VI, and TLE4, a marker of corticothalamic projection neurons (CThPNs) in layer VI, of the cortex. A birthdating analysis using 5-ethynyl-2'-deoxyuridine at embryonic day (E)11.5, 5-bromo-2'-deoxyuridine at E12.5, and in utero electroporation of a GFP expression plasmid at E14.5 revealed a reduction in the percentage of neurons produced at E11.5 in layer VI/subplate of the cortex and in the ganglion cell layer of the retina in P0 Fut9^-/- mice. Furthermore, this reduction in layer VI/subplate neurons persisted into adulthood, leading to a reduction in the number of Ctip2^strong/Satb2^- excitatory neurons in layer V/VI of the adult Fut9^-/- cortex. These results suggest that Fut9 plays significant roles in the differentiation, migration, and maturation of neural precursor cells in the cortex and retina.

Precise CAG repeat contraction in a Huntington's Disease mouse model is enabled by gene editing with SpCas9-NG

The clustered regularly interspaced palindromic repeats (CRISPR)/Cas9 system is a research hotspot in gene therapy. However, the widely used Streptococcus pyogenes Cas9 (WT-SpCas9) requires an NGG protospacer adjacent motif (PAM) for target recognition, thereby restricting targetable disease mutations. To address this issue, we recently reported an engineered SpCas9 nuclease variant (SpCas9-NG) recognizing NGN PAMs. Here, as a feasibility study, we report SpCas9-NG-mediated repair of the abnormally expanded CAG repeat tract in Huntington's disease (HD). By targeting the boundary of CAG repeats with SpCas9-NG, we precisely contracted the repeat tracts in HD-mouse-derived embryonic stem (ES) cells. Further, we confirmed the recovery of phenotypic abnormalities in differentiated neurons and animals produced from repaired ES cells. Our study shows that SpCas9-NG can be a powerful tool for repairing abnormally expanded CAG repeats as well as other disease mutations that are difficult to access with WT-SpCas9.

Life-Long Neural Stem Cells Are Fate-Specified at an Early Developmental Stage

The origin and life-long fate of quiescent neural stem cells (NSCs) in the adult mammalian brain remain largely unknown. A few neural precursor cells in the embryonic brain elongate their cell cycle time and subsequently become quiescent postnatally, suggesting the possibility that life-long NSCs are selected at an early embryonic stage. Here, we utilized a GFP-expressing lentivirus to investigate the fate of progeny from individual lentivirus-infected NSCs by identifying the lentiviral integration site. Our data suggest that NSCs become specified to two or more lineages prior to embryonic day 13.5 in mice: one NSC lineage produces cells only for the cortex and another provides neurons to the olfactory bulb. The majority of neurosphere-forming NSCs in the adult brain are relatively dormant and generate very few cells, if any, in the olfactory bulb or cortex, and this NSC population could serve as a reservoir that is occasionally reactivated later in life.

Comprehensive evaluation of ubiquitous promoters suitable for the generation of transgenic cynomolgus monkeys†

Nonhuman primates (NHPs) are considered to be the most valuable models for human transgenic (Tg) research into disease because human pathology is more closely recapitulated in NHPs than rodents. Previous studies have reported the generation of Tg NHPs that ubiquitously overexpress a transgene using various promoters, but it is not yet clear which promoter is most suitable for the generation of NHPs overexpressing a transgene ubiquitously and persistently in various tissues. To clarify this issue, we evaluated four putative ubiquitous promoters, cytomegalovirus (CMV) immediate-early enhancer and chicken beta-actin (CAG), elongation factor 1α (EF1α), ubiquitin C (UbC), and CMV, using an in vitro differentiation system of cynomolgus monkey embryonic stem cells (ESCs). While the EF1α promoter drove Tg expression more strongly than the other promoters in undifferentiated pluripotent ESCs, the CAG promoter was more effective in differentiated cells such as embryoid bodies and ESC-derived neurons. When the CAG and EF1α promoters were used to generate green fluorescent protein (GFP)-expressing Tg monkeys, the CAG promoter drove GFP expression in skin and hematopoietic tissues more strongly than in ΕF1α-GFP Tg monkeys. Notably, the EF1α promoter underwent more silencing in both ESCs and Tg monkeys. Thus, the CAG promoter appears to be the most suitable for ubiquitous and stable expression of transgenes in the differentiated tissues of Tg cynomolgus monkeys and appropriate for the establishment of human disease models.

Early Maternal and Social Deprivation Expands Neural Stem Cell Population Size and Reduces Hippocampus/Amygdala-Dependent Fear Memory

Early life stress can exert detrimental or beneficial effects on neural development and postnatal behavior depending on the timing, duration, strength, and ability to control the stressors. In this study, we utilized a maternal and social deprivation (MSD) model to investigate the effects of early life stress on neural stem cells (NSCs) and neurogenesis in the adult brain. We found that MSD during the stress-hyporesponsive period (SHRP) (early-MSD), when corticosterone secretion is suppressed, increased the size of the NSC population, whereas the same stress beyond the SHRP abrogated these effects. Early-MSD enhanced neurogenesis not only in the dentate gyrus of the hippocampus, one of the classic neurogenic regions, but also in the amygdala. In addition, mice exposed to early-MSD exhibited a reduction in amygdala/hippocampus-dependent fear memory. These results suggest that animals exposed to early life stress during the SHRP have reinforced stress resilience to cope with perceived stressors to maintain a normal homeostatic state.

Adult neurogenesis and its role in brain injury and psychiatric diseases

In the adult mammalian brain, neural stem cells (NSCs) reside in two neurogenic regions, the walls of the lateral ventricles, and the subgranular zone of the hippocampus, which generate new neurons for the olfactory bulb and dentate gyrus, respectively. These adult NSCs retain their self-renewal ability and capacity to differentiate into neurons and glia as demonstrated by in vitro studies. However, their contribution to tissue repair in disease and injury is limited, lending credence to the claim by prominent neuropathologist Ramón y Cajal that 'once development was ended, the founts of growth and regeneration of the axons and dendrites dried up irrevocably'. However, recent progress toward understanding the fundamental biology of adult NSCs and their role in pathological conditions has provided new insight into the potential therapeutic utility of endogenous NSCs. In this short review, we highlight two topics: the altered behavior of NSCs after brain damage and the dysfunction of NSCs and oligodendrocyte precursor cells, another type of undifferentiated cell in the adult brain, in mood affective disorders.

Minocycline Directly Enhances the Self-Renewal of Adult Neural Precursor Cells

Minocycline not only has antibacterial action but also produces a variety of pharmacological effects. It has drawn considerable attention as a therapeutic agent for symptoms caused by inflammation in many neurological disorders, leading to several clinical trials. Although some of these effects are mediated through its function of suppressing microglial activation, it is not clear whether minocycline acts on other cell types in the adult brain. In this study, we utilized a colony-forming neurosphere assay, in which neural stem cells (NSCs) clonally proliferate to form floating colonies, called neurospheres. We found that minocycline (at therapeutically relevant concentrations in cerebrospinal fluid) enhances the self-renewal capability of NSCs derived from the subependymal zone of adult mouse brain and facilitates their differentiation into oligodendrocytes. Importantly, these effects were independent of a suppression of microglial activation and were specifically observed with minocycline (among tetracycline derivatives). In addition, the size of the NSC population in the adult brain was increased when minocycline was infused into the lateral ventricle by an osmotic minipump in vivo. While precise molecular mechanisms of how minocycline alters the behavior of adult NSCs remain unknown, our data provide a basis for the clinical use of minocycline to treat neurodegenerative and demyelinating diseases.

Origin of oligodendrocytes in mammalian forebrains: a revised perspective

Oligodendrocyte precursor cells (OPCs) appear in the late embryonic brain, mature into oligodendrocytes (OLs), and form myelin in the postnatal brain. It has been proposed that early born OPCs derived from the ventral forebrain are eliminated postnatally and late-born OLs predominate in the adult mouse cortex. However, the temporal and regional niche for cortical OL generation, which persists throughout life in adult mammals, remains to be determined. Our recent study provides new insight into self-renewing and multipotent neural stem cells (NSCs). Our results, together with previous studies, suggest that NSCs at the dorsoventral boundary are uniquely specialized to produce myelin-forming OLs in the cortex during a restricted temporal window. These findings may help identify transcription factors or gene expression patterns which confer neural precursors with the characteristic ability of dorsoventral boundary NSCs to differentiate into OLs, and facilitate the development of new strategies for regenerative medicine of the damaged brain.

Generation of transgenic cynomolgus monkeys that express green fluorescent protein throughout the whole body

Nonhuman primates are valuable for human disease modelling, because rodents poorly recapitulate some human diseases such as Parkinson’s disease and Alzheimer’s disease amongst others. Here, we report for the first time, the generation of green fluorescent protein (GFP) transgenic cynomolgus monkeys by lentivirus infection. Our data show that the use of a human cytomegalovirus immediate-early enhancer and chicken beta actin promoter (CAG) directed the ubiquitous expression of the transgene in cynomolgus monkeys. We also found that injection into mature oocytes before fertilization achieved homogenous expression of GFP in each tissue, including the amnion, and fibroblasts, whereas injection into fertilized oocytes generated a transgenic cynomolgus monkey with mosaic GFP expression. Thus, the injection timing was important to create transgenic cynomolgus monkeys that expressed GFP homogenously in each of the various tissues. The strategy established in this work will be useful for the generation of transgenic cynomolgus monkeys for transplantation studies as well as biomedical research.

Determination of major sialylated N-glycans and identification of branched sialylated N-glycans that dynamically change their content during development in the mouse cerebral cortex

Oligosaccharides of glycoproteins expressed on the cell surface play important roles in cell-cell interactions, particularly sialylated N-glycans having a negative charge, which interact with sialic acid-binding immunoglobulin-like lectins (siglecs). The entire structure of sialylated N-glycans expressed in the mouse brain, particularly the linkage type of sialic acid residues attached to the backbone N-glycans, has not yet been elucidated. An improved method to analyze pyridylaminated sugar chains using high performance liquid chromatography (HPLC) was developed to determine the entire structure of sialylated N-linked sugar chains expressed in the adult and developing mouse cerebral cortices. Three classes of sialylated sugar chains were prevalent: 1) N-glycans containing α(2-3)-sialyl linkages on a type 2 antennary (Galβ(1-4)GlcNAc), 2) sialylated N-glycans with α(2-6)-sialyl linkages on a type 2 antennary, and 3) a branched sialylated N-glycan with a [Galβ(1-3){NeuAcα(2-6)}GlcNAc-] structure, which was absent at embryonic day 12 but then increased during development. This branched type sialylated N-glycan structure comprised approximately 2 % of the total N-glycans in the adult brain. Some N-glycans (containing type 2 antennary) were found to change their type of sialic acid linkage from α(2-6)-Gal to α(2-3)-Gal. Thus, the linkages and expression levels of sialylated N-glycans change dramatically during brain development.

Heterozygous Polg mutation causes motor dysfunction due to mtDNA deletions

Objective

Mutations in nuclear-encoded mitochondrial DNA (mtDNA) polymerase (POLG) are known to cause autosomal dominant chronic progressive external ophthalmoplegia (adCPEO) with accumulation of multiple mtDNA deletions in muscles. However, no animal model with a heterozygous Polg mutation representing mtDNA impairment and symptoms of CPEO has been established. To understand the pathogenic mechanism of CPEO, it is important to determine the age dependency and tissue specificity of mtDNA impairment resulting from a heterozygous mutation in the Polg gene in an animal model.

Methods

We assessed behavioral phenotypes, tissue-specific accumulation of mtDNA deletions, and its age dependency in heterozygous Polg^D257A knock-in mice carrying a proofreading-deficient mutation in the Polg.

Results

Heterozygous Polg^D257A knock-in mice exhibited motor dysfunction in a rotarod test. Polg^+/D257A mice had significant accumulation of multiple mtDNA deletions, but did not show significant accumulation of point mutations or mtDNA depletion in the brain. While mtDNA deletions increased in an age-dependent manner regardless of the tissue even in Polg^+/+ mice, the age-dependent accumulation of mtDNA deletions was enhanced in muscles and in the brain of Polg^+/D257A mice.

Interpretation

Heterozygous Polg^D257A knock-in mice showed tissue-specific, age-dependent accumulation of multiple mtDNA deletions in muscles and the brain which was likely to result in neuromuscular symptoms. Polg^+/D257A mice may be used as an animal model of adCPEO associated with impaired mtDNA maintenance.

The Lewis X-related α1,3-fucosyltransferase, Fut10, is required for the maintenance of stem cell populations

Lewis X (Le(X), Galβ1-4(Fucα1-3)GlcNAc) is a carbohydrate epitope that is present at the nonreducing terminus of sugar chains of glycoproteins and glycolipids, and is abundantly expressed in several stem cell populations. Le(X) antigen can be used in conjunction with fluorescence-activated cell sorting to isolate neurosphere-forming neural stem cells (NSCs) from embryonic mouse brains. However, its function in the maintenance and differentiation of stem cells remains largely unknown. In this study, we examined mice deficient for fucosyltransferase 9 (Fut9), which is thought to synthesize most, if not all, of the Le(X) moieties in the brain. We found that the number of NSCs was increased in the brain of Fut9(-/-) embryos, suggesting that Fut9-synthesized Le(X) is dispensable for the maintenance of NSCs. Another α1,3-fucosyltransferase gene, fucosyltransferase 10 (Fut10), is expressed in the ventricular zone of the embryonic brain. Overexpression of Fut10 enhanced the self-renewal of NSCs. Conversely, suppression of Fut10 expression induced the differentiation of NSCs and embryonic stem cells. In addition, knockdown of Fut10 expression in the cortical ventricular zone of the embryonic brain by in utero electroporation of Fut10-miRNAs impaired the radial migration of neural precursor cells. Our data suggest that Fut10 is involved in a unique α1,3-fucosyltransferase activity with stringent substrate specificity, and that this activity is required to maintain stem cells in an undifferentiated state.

[Regenerative strategy for autoimmune neurological diseases using neural stem cells]

Autoimmune demyelinating diseases of central nervous system are relatively uncommon in Asian but, when proceeds to chronic state, disabling neurological conditions. Recent advance in developing disease-modifying reagents for chronic stage of multiple sclerosis is not yet satisfactory and new strategies of therapy are waited. Neural stem cells, which exist in the subependyma and the dentate gyrus of hippocampus of the adult mammalian brain, could be utilized to provide myelin-forming oligodendrocytes and restore function. Some drugs, which are used in clinics, exhibit direct effects on adult neural stem cells to enhance their self-renewal capability and survival and to promote oligodendrocyte differentiation. Alternatively, oligodendrocyte precursor cells derived from iPS cells 3an be transplanted to the demyelinating brains, where the cells extensively migrate out to myelinate naked axons.

Olig2-lineage cells preferentially differentiate into oligodendrocytes but their processes degenerate at the chronic demyelinating stage of proteolipid protein-overexpressing mouse

In chronic demyelinating lesions of the central nervous system, insufficient generation of oligodendrocytes (OLs) is not due to a lack of oligodendrocyte precursor cells (OPCs), because the accumulation of OPCs and premyelinating OLs can be observed within these lesions. Here we sought to identify the basis for the failure of OLs to achieve terminal differentiation in chronic demyelinating lesions through the utilization of plp1-overexpressing (Plp(tg/-)) mice. These mice are characterized by progressive demyelination in young adults and chronic demyelinating lesions at more mature stages. We show that neural stem cells, which are the precursors of OL-lineage cells, are present in the Plp(tg/-) mouse brain and that their multipotentiality and ability to self-renew are comparable to those of wild-type adults in culture. Lineage-tracing experiments using a transgenic mouse line, in which an inducible Cre recombinase is knocked in at the Olig2 locus, revealed that Olig2-lineage cells preferentially differentiated into OPCs and premyelinating OLs, but not into astrocytes, in the Plp(tg/-) mouse brain. These Olig2-lineage cells matured to express myelin basic protein but after that their processes degenerated in the chronic demyelinating lesions of the Plp(tg/-) brain. These results indicate that in chronic demyelinated lesions more OL-lineage cells are produced as part of the repair process, but their processes degenerate after maturation.

MafB interacts with Gcm2 and regulates parathyroid hormone expression and parathyroid development

Serum calcium and phosphate homeostasis is critically regulated by parathyroid hormone (PTH) secreted by the parathyroid glands. Parathyroid glands develop from the bilateral parathyroid-thymus common primordia. In mice, the expression of transcription factor Glial cell missing 2 (Gcm2) begins in the dorsal/anterior part of the primordium on embryonic day 9.5 (E9.5), specifying the parathyroid domain. The parathyroid primordium then separates from the thymus primordium and migrates to its adult location beside the thyroid gland by E15.5. Genetic ablation of gcm2 results in parathyroid agenesis in mice, indicating that Gcm2 is essential for early parathyroid organogenesis. However, the regulation of parathyroid development at later stages is not well understood. Here we show that transcriptional activator v-maf musculoaponeurotic fibrosarcoma oncogene homologue B (MafB) is developmentally expressed in parathyroid cells after E11.5. MafB expression was lost in the parathyroid primordium of gcm2 null mice. The parathyroid glands of mafB(+/-) mice were mislocalized between the thymus and thyroid. In mafB(-/-) mice, the parathyroid did not separate from the thymus. Furthermore, in mafB(-/-) mice, PTH expression and secretion were impaired; expression levels of renal cyp27b1, one of the target genes of PTH, was decreased; and bone mineralization was reduced. We also demonstrate that although Gcm2 alone does not stimulate the PTH gene promoter, it associates with MafB to synergistically activate PTH expression. Taken together, our results suggest that MafB regulates later steps of parathyroid development, that is, separation from the thymus and migration toward the thyroid. MafB also regulates the expression of PTH in cooperation with Gcm2.

Neuron-specific gene transfer through retrograde transport of lentiviral vector pseudotyped with a novel type of fusion envelope glycoprotein

The lentiviral vector system is used extensively in gene therapy trials for various neurological and neurodegenerative disorders. The vector system permits efficient and sustained gene expression in many cell types through integration of the transgene into the host cell genome. However, there is a significant issue concerning the therapeutic use of lentiviral vectors, that transgene insertion may lead to tumorigenesis by altering the expression of proto-oncogenes adjacent to the integration sites. One useful approach for improving safety is to restrict vector transduction to neuronal cells. We have reported the use of human immunodeficiency virus type 1 (HIV-1)-based vectors for efficient retrograde transport by pseudotyping with rabies virus glycoprotein (RV-G) or fusion glycoprotein B type, in which the cytoplasmic domain of RV-G was substituted with the counterpart of vesicular stomatitis virus glycoprotein (VSV-G). Here we developed a novel vector system for neuron-specific retrograde gene transfer (termed NeuRet) by pseudotyping the HIV-1 vector with fusion glycoprotein C type (FuG-C), in which a short C-terminal segment of the extracellular domain and the transmembrane/cytoplasmic domains of RV-G were replaced with the corresponding regions of VSV-G. FuG-C pseudotyping caused efficient gene transfer, mainly through retrograde transport, into neuronal cells in diverse brain regions, whereas the pseudotyping resulted in less efficiency for the transduction of glial and neural stem/progenitor cells. Our NeuRet vector system achieves efficient retrograde gene delivery for therapeutic trials and improves their safety by greatly reducing the risk of gene transduction of dividing cells in the brain.

Functional central nervous system myelin repair in an adult mouse model of demyelination caused by proteolipid protein overexpression

Two types of interventions to remyelinate the adult demyelinated central nervous system were investigated in heterozygous transgenic mice overexpressing the proteolipid protein gene. 1) A cocktail of trophic factors, "TS1," was directed toward the activation of the endogenous pool of neural progenitors to increase the number of myelinating oligodendrocytes (OL) in the brain. 2) A combinatorial approach in which OL progenitors were coinjected with TS1 into the corpus callosum of wild-type and He4e transgenic mice that displayed hindlimb paralysis. The levels of locomotor ability in these mice were evaluated after a single treatment. The data showed that a single administration of either one of the interventions had similar therapeutic effects, alleviating the symptoms of demyelination and leading to the recovery of hindlimb function. Histological and immunofluorescent examination of brain sections showed extensive remyelination that was sufficient to reverse hindlimb paralysis in transgenic mice. When the interventions were administered prior to hindlimb paralysis, He4e mice were able to walk up to 1 year of age without paralysis.

[Understanding the pathogenesis of mood affective disorders through the study of neural stem cell biology]

Adult neurogenesis occurs in the olfactory bulb and the dentate gyrus of the hippocampus. It has been shown that exposure to psychosocial stress reduces cell proliferation in the dentate gyrus. However, little is known about how stress affects the proliferation kinetics of neural stem cells (NSCs) in the adult brain. We utilized a forced swim model of stress in the mouse and found that chronic stress decreased the number of NSCs. The reduction in NSC number persisted for weeks after the cessation of stress, but was reversed by treatment with antidepressant drugs, fluoxetine and imipramine. However, these antidepressants exhibit no direct effects on NSCs, suggesting that the effects of antidepressants on NSCs are mediated by serotonin. In contrast, mood stabilizing drugs, which are used to treat patients with bipolar disorder, act cell-autonomously on NSCs and enhance their self-renewal capability. Importantly, this enhancement is achieved at therapeutically relevant concentrations in the cerebrospinal fluid. The pharmacological effects are mediated by the activation of Notch signaling in the NSC, but not by the inhibition of GSK-3b signaling or inositol depletion, currently popular models to explain mood stabilizers' action. These data provide insights into the molecular mechanisms underlying the pathogenesis of mood affective disorders.

Heparan sulfate regulates self-renewal and pluripotency of embryonic stem cells

Embryonic stem (ES) cell self-renewal and pluripotency are maintained by several signaling cascades and by expression of intrinsic factors, such as Oct3/4 and Nanog. The signaling cascades are activated by extrinsic factors, such as leukemia inhibitory factor, bone morphogenic protein, and Wnt. However, the mechanism that regulates extrinsic signaling in ES cells is unknown. Heparan sulfate (HS) chains are ubiquitously present as the cell surface proteoglycans and are known to play crucial roles in regulating several signaling pathways. Here we investigated whether HS chains on ES cells are involved in regulating signaling pathways that are important for the maintenance of ES cells. RNA interference-mediated knockdown of HS chain elongation inhibited mouse ES cell self-renewal and induced spontaneous differentiation of the cells into extraembryonic endoderm. Furthermore, autocrine/paracrine Wnt/beta-catenin signaling through HS chains was found to be required for the regulation of Nanog expression. We propose that HS chains are important for the extrinsic signaling required for mouse ES cell self-renewal and pluripotency.

Adhesion is prerequisite, but alone insufficient, to elicit stem cell pluripotency

Primitive mammalian neural stem cells (NSCs), arising during the earliest stages of embryogenesis, possess pluripotency in embryo chimera assays in contrast to definitive NSCs found in the adult. We hypothesized that adhesive differences determine the association of stem cells with embryonic cells in chimera assays and hence their ability to contribute to later tissues. We show that primitive NSCs and definitive NSCs possess adhesive differences, resulting from differential cadherin expression, that lead to a double dissociation in outcomes after introduction into the early- versus midgestation embryo. Primitive NSCs are able to sort with the cells of the inner cell mass and thus contribute to early embryogenesis, in contrast to definitive NSCs, which cannot. Conversely, primitive NSCs sort away from cells of the embryonic day 9.5 telencephalon and are unable to contribute to neural tissues at midembryogenesis, in contrast to definitive NSCs, which can. Overcoming these adhesive differences by E-cadherin overexpression allows some definitive NSCs to integrate into the inner cell mass but is insufficient to allow them to contribute to later development. These adhesive differences suggest an evolving compartmentalization in multipotent NSCs during development and serve to illustrate the importance of cell-cell association for revealing cellular contribution.

Antidepressant drugs reverse the loss of adult neural stem cells following chronic stress

In rodents, adult neurogenesis occurs in the olfactory bulb and the dentate gyrus of the hippocampus. It has been shown that exposure to psychosocial stress reduces cell proliferation in the dentate gyrus. However, little is known about how stress affects the proliferation kinetics of neural stem cells (NSCs) in the subventricular zone (SVZ), which provide new neurons to the olfactory bulb. We utilized a forced-swim model of stress in the mouse and found that chronic stress decreased the number of NSCs in the SVZ. The reduction of NSC number persisted for weeks after the cessation of stress but was reversed by treatment with the antidepressant drugs fluoxetine and imipramine. We demonstrated by in vitro colony-forming neurosphere assay that corticosterone attenuated neurosphere formation by adult NSCs and, in contrast, that serotonin increased the survival of NSCs. In addition, serotonin expanded the size of the NSC pool in the SVZ when it was infused into the lateral ventricle in vivo. These results suggest that, under chronic stress conditions, the number of NSCs is regulated by the actions of glucocorticoids and serotonin. These data provide insights into the molecular mechanisms underlying the pharmacological actions of antidepressant drugs.

Developmental changes in the expression of glycogenes and the content of N-glycans in the mouse cerebral cortex

Biosynthesis of N-glycans varies significantly among tissues and is strictly regulated spatially and temporally within the tissue. The strict molecular mechanisms that are responsible for control of N-glycan synthesis remain largely unknown. We developed complementary deoxyribonucleic acid (cDNA) macroarray system and analyzed gene expression levels of more than 140 glycosyltransferases and glycosidases in the cerebral cortex from developing and adult mice. We also analyzed the relative amounts of major N-glycans present in the cerebral cortex and examined how the synthesis of N-glycans might be regulated through the expression of these genes. We demonstrated that the content of N-linked oligosaccharides dramatically changed during the course of brain development. Some of these changes could not be explained by alterations in the expression of the corresponding genes. For example, the amount of core fucosylated sugar chains in the early embryonic brain and the expression level of fucosyltransferase VIII, the only gene known to be responsible for core fucosylation, did not change proportionately. This result suggests that post-transcriptional regulation of this gene plays an important role in regulating its enzymatic activity. On the other hand, the amount of beta1,3-galactose residue-containing sugar chains increased postnatally following an increase in the level of beta1,3-galactosyltransferase messenger ribonucleic acid (mRNA). Furthermore, the amount of sugar chains with an outer fucose residue, containing LewisX-BA-2, correlated well with the expression of fusocyltransferase IX mRNA. These findings add to our understanding of the molecular mechanisms responsible for the regulation of N-glycan biosynthesis in the cerebral cortex.

Regulation of glial development by cystatin C

Cystatin C (CysC) is an endogenous cysteine proteases inhibitor produced by mature astrocytes in the adult brain. Previously we isolated CysC as a factor activating the glial fibrillary acidic protein (GFAP) promoter, and showed that CysC is expressed in astrocyte progenitors during development. Here we show that protease inhibitor activity increased daily in conditioned medium, and that this activity was mainly a result of CysC released from primary cultured cells. Human CysC added to the culture medium of primary brain cells increased the number of GFAP-positive and nestin-positive cells. Human CysC also increased the number of neurospheres formed from embryonic brain, and thus it increases the number of neural stem/precursor cells in a manner similar to glycosylated rat CysC. The addition of a neutralizing antibody, on the other hand, greatly decreased the number of GFAP and glutamate aspartate transporter (GLAST)-positive astrocytes. This decrease was reversed by the addition of CysC but not by another cysteine protease inhibitor. Thus, the promotion of astrocyte development by CysC appears to be independent of its protease inhibitor activity. The antibody increased the number of oligodendrocytes and their precursors. Therefore, CysC modifies glial development in addition to its activity against neural stem/precursor cells.

Vascular endothelial growth factor directly inhibits primitive neural stem cell survival but promotes definitive neural stem cell survival

There are two types of neural stem cells (NSCs). Primitive NSCs [leukemia inhibitory factor (LIF) dependent but exogenous fibroblast growth factor (FGF) 2 independent] can be derived from mouse embryonic stem (ES) cells in vitro and from embryonic day 5.5 (E5.5) to E7.5 epiblast and E7.5-E8.5 neuroectoderm in vivo. Definitive NSCs (LIF independent but FGF2 dependent) first appear in the E8.5 neural plate and persist throughout life. Primitive NSCs give rise to definitive NSCs. Loss and gain of functions were used to study the role of vascular endothelial growth factor (VEGF)-A and its receptor, Flk1, in NSCs. The numbers of Flk1 knock-out mice embryo-derived and ES cell-derived primitive NSCs were increased because of the enhanced survival of primitive NSCs. In contrast, neural precursor-specific, Flk1 conditional knock-out mice-derived, definitive NSCs numbers were decreased because of the enhanced cell death of definitive NSCs. These effects were not observed in cells lacking Flt1, another VEGF receptor. In addition, the cell death stimulated by VEGF-A of primitive NSC and the cell survival stimulated by VEGF-A of definitive NSC were blocked by Flk1/Fc-soluble receptors and VEGF-A function-blocking antibodies. These VEGF-A phenotypes also were blocked by inhibition of the downstream effector nuclear factor kappaB (NF-kappaB). Thus, both the cell death of primitive NSC and the cell survival of definitive NSC induced by VEGF-A stimulation are mediated by bifunctional NF-kappaB effects. In conclusion, VEGF-A function through Flk1 mediates survival (and not proliferative or fate change) effects on NSCs, specifically.

Notch signaling is required to maintain all neural stem cell populations--irrespective of spatial or temporal niche

Recently, Notch signaling has been reported to underscore the ability of neural stem cells (NSCs) to self-renew. Utilizing mice deficient in presenilin-1(PS1), we asked whether the function of Notch signaling in NSC maintenance was conserved. At embryonic day 14.5, all NSCs--both similar (cortex-, ganglionic eminence- and hindbrain-derived) and distinct (retinal stem cell)--require Notch signaling in a gene-dosage-sensitive manner to undergo expansionary symmetric divisions, as assessed by the clonal, in vitro neurosphere assay. Within the adult, however, Notch signaling modulates cell cycle time in order to ensure brain-derived NSCs retain their self-renewal property. At face value, the effects in the embryo and adult appear different. We propose potential hypotheses, including the ability of cell cycle to modify the mode of division, in order to resolve this discrepancy. Regardless, these findings demonstrate that PS1, and presumably Notch signaling, is required to maintain all NSCs.

Induction of oligodendrocyte progenitors in dorsal forebrain by intraventricular microinjection of FGF-2

During embryonic development, oligodendrocyte progenitors (OLPs) originate from the ventral forebrain under the regulation of Sonic hedgehog (Shh). Shh controls the expression of transcription factor Olig2, which is strongly implicated in OLP generation. Studies of mice deficient in Shh expression suggest, however, that an alternative pathway for OLP generation may exist. The generation of OLPs in dorsal forebrain has been suggested since treatment of dorsal-neural progenitor cells in culture with fibroblast growth factor (FGF-2) results in OLP induction. To ask if dorsal induction of OLPs in embryonic forebrain can occur in vivo and if FGF-2 could initiate an alternative pathway of regulation, we used in utero microinjection of FGF-2 into the lateral ventricles of mouse fetal forebrain. A single injection of FGF-2 at E13.5 resulted in the expression of the OLP markers Olig2 and PDGFRalpha mRNA in dorsal forebrain ventricular and intermediate zones. However, FGF-2 did not induce dorsal expression of Shh, Patched1 or Nkx2.1, and co-injection of FGF-2 and a Shh inhibitor did not attenuate the induction of Olig2 and PDGFRalpha, suggesting that Shh signaling was not involved in this FGF-2-mediated dorsal induction. These results demonstrate that the dorsal embryonic forebrain in vivo has the potential to generate OLPs in the presence of normal positional cues and that this can be driven by FGF-2 independent of Shh signaling.

An N-glycan structure correlates with pulmonary metastatic ability of cancer cells

N-Glycan structures on the surface of cancer cells have diverse structures and play significant roles in metastatic process. However, little is known about their roles in organ-selective metastasis. Our study revealed that an alpha1,6-fucosylated biantennary N-glycan structure designated A2G2F is characteristic of lungs, with far more abundant expression in normal human and murine lungs than in other organs. In this study, we further examined the role of A2G2F in pulmonary metastasis. We stained metastatic cancers by alpha1,6-fucose-specific Lens culinaris agglutinin lectin and revealed that pulmonary metastatic nodules more abundantly expressed alpha1,6-fucosylated N-glycans than hepatic metastatic nodules from common primary cancers. The most specific alpha1,6-fucosylated N-glycan structure in pulmonary metastatic cancer was identified to be A2G2F. Using a B16 melanoma cell metastasis model, we showed that A2G2F-rich B16 cells formed more pulmonary metastatic nodules than A2G2F-poor cells. Our results suggest that A2G2F plays a critical role in pulmonary metastasis.

Primitive neural stem cells from the mammalian epiblast differentiate to definitive neural stem cells under the control of Notch signaling

Basic fibroblast growth factor (FGF2)-responsive definitive neural stem cells first appear in embryonic day 8.5 (E8.5) mouse embryos, but not in earlier embryos, although neural tissue exists at E7.5. Here, we demonstrate that leukemia inhibitory factor-dependent (but not FGF2-dependent) sphere-forming cells are present in the earlier (E5.5-E7.5) mouse embryo. The resultant clonal sphere cells possess self-renewal capacity and neural multipotentiality, cardinal features of the neural stem cell. However, they also retain some nonneural properties, suggesting that they are the in vivo cells' equivalent of the primitive neural stem cells that form in vitro from embryonic stem cells. The generation of the in vivo primitive neural stem cell was independent of Notch signaling, but the activation of the Notch pathway was important for the transition from the primitive to full definitive neural stem cell properties and for the maintenance of the definitive neural stem cell state.

[The generation of neural stem cells: induction of neural stem cells from embryonic stem (ES) cells]

Neural stem cells are considered the ultimate lineage precursors to all neurons and glia. Despite the significance of neural stem cells in the mammalian brain development, their ontogenesis remains unclear. We have established a colony-forming embryonic stem (ES) sphere assay, where ES cells were cultured in serum-free media in the presence of leukemia inhibitory factor (LIF) to form floating spheres. LIF-dependent ES cell-derived sphere cells showed self-renewal and neural multipotentiality, cardinal features of the neural stem cell, but retained some non-neural properties and broader potential. We dabbed the cells in the ES cell-derived sphere of primitive neural stem cells. LIF-dependent sphere-forming cells were also present in the epiblast of embryonic day 5.5-7.5 mouse embryos. The generation of the in vivo primitive neural stem cell was independent of Notch signaling but the activation of Notch pathway was necessary for the transition from the primitive neural stem cell to the neural stem cell. We propose that the neural stem cell originates from the pluripotent inner cell mass/epiblast cell via the primitive neural stem cell stage under the control of Notch signaling.

Binding of immunoglobulin G antibodies in Guillain-Barré syndrome sera to a mixture of GM1 and a phospholipid: possible clinical implications

Anti-GM1 immunoglobulin G (IgG) antibodies are frequently present in sera from patients with Guillain-Barré syndrome (GBS). A previous report on a patient who had a neuropathy with immunoglobulin M (IgM) M-protein binding to a conformational epitope formed by phosphatidic acid (PA) and gangliosides prompted us to investigate the binding of IgG antibodies in GBS sera to a mixture of GM1 and PA (GM1/PA). Of 121 GBS patients, 32 had anti-GM1 IgG antibodies. All 32 also had antibody activity against GM1/PA. Twenty-five (78%) of 32 patients had greater activity against GM1/PA than against GM1 alone. Twelve patients who had no anti-GM1 IgG antibodies had IgG antibody activity against GM1/PA. No GBS patient had IgG antibody against PA alone. In contrast, two rabbit anti-GM1 antisera had greater activity against GM1 alone than against GM1/PA. IgG antibody with greater binding activity against a mixture of GM1 and a phospholipid than against GM1 alone may have an important role in the pathogenesis of GBS and has implications for diagnosis.

Notch pathway molecules are essential for the maintenance, but not the generation, of mammalian neural stem cells

Neural stem cells, which exhibit self-renewal and multipotentiality, are generated in early embryonic brains and maintained throughout the lifespan. The mechanisms of their generation and maintenance are largely unknown. Here, we show that neural stem cells are generated independent of RBP-Jkappa, a key molecule in Notch signaling, by using RBP-Jkappa(-/-) embryonic stem cells in an embryonic stem cell-derived neurosphere assay. However, Notch pathway molecules are essential for the maintenance of neural stem cells; they are depleted in the early embryonic brains of RBP-Jkappa(-/-) or Notch1(-/-) mice. Neural stem cells also are depleted in embryonic brains deficient for the presenilin1 (PS1) gene, a key regulator in Notch signaling, and are reduced in PS1(+/-) adult brains. Both neuronal and glial differentiation in vitro were enhanced by attenuation of Notch signaling and suppressed by expressing an active form of Notch1. These data are consistent with a role for Notch signaling in the maintenance of the neural stem cell, and inconsistent with a role in a neuronal/glial fate switch.

Neural stem cell lineages are regionally specified, but not committed, within distinct compartments of the developing brain

Regional patterning in the developing mammalian brain is partially regulated by restricted gene expression patterns within the germinal zone, which is composed of stem cells and their progenitor cell progeny. Whether or not neural stem cells, which are considered at the top of the neural lineage hierarchy, are regionally specified remains unknown. Here we show that the cardinal properties of neural stem cells (self-renewal and multipotentiality) are conserved among embryonic cortex, ganglionic eminence and midbrain/hindbrain, but that these different stem cells express separate molecular markers of regional identity in vitro, even after passaging. Neural stem cell progeny derived from ganglionic eminence but not from other regions are specified to respond to local environmental cues to migrate ventrolaterally, when initially deposited on the germinal layer of ganglionic eminence in organotypic slice cultures. Cues exclusively from the ventral forebrain in a 5 day co-culture paradigm could induce both early onset and late onset marker gene expression of regional identity in neural stem cell colonies derived from both the dorsal and ventral forebrain as well as from the midbrain/hindbrain. Thus, neural stem cells and their progeny are regionally specified in the developing brain, but this regional identity can be altered by local inductive cues.

Direct neural fate specification from embryonic stem cells: a primitive mammalian neural stem cell stage acquired through a default mechanism

Little is known about how neural stem cells are formed initially during development. We investigated whether a default mechanism of neural specification could regulate acquisition of neural stem cell identity directly from embryonic stem (ES) cells. ES cells cultured in defined, low-density conditions readily acquire a neural identity. We characterize a novel primitive neural stem cell as a component of neural lineage specification that is negatively regulated by TGFbeta-related signaling. Primitive neural stem cells have distinct growth factor requirements, express neural precursor markers, generate neurons and glia in vitro, and have neural and non-neural lineage potential in vivo. These results are consistent with a default mechanism for neural fate specification and support a model whereby definitive neural stem cell formation is preceded by a primitive neural stem cell stage during neural lineage commitment.

Degeneration of rabbit sensory neurons induced by passive transfer of anti-GD1b antiserum

Systemic infusion of high-titer anti-GD1b antiserum to two rabbits pre-inoculated with keyhole limpet hemocyanin and Freund's complete adjuvant was performed. The two rabbits had low-titer anti-GD1b antibody in sera. Although no apparent clinical signs were observed, pathological examinations showed vacuolar degeneration with macrophage infiltration in a few axons in the dorsal columns of the spinal cords from the two rabbits. No such pathological changes were observed in the other two pre-inoculated rabbits infused with normal rabbit sera. Anti-GD1b antibody therefore may cause degeneration in rabbit sensory neurons with central axons extending to the dorsal column.

Monospecific anti-GD1b IgG is required to induce rabbit ataxic neuropathy

Of 22 rabbits sensitized with GD1b, 12 developed experimental sensory ataxic neuropathy. The affected rabbits had a higher level of serum IgG monospecific to GD1b than the unaffected ones. The GD1b-positive neuronal cytoplasms of rabbit dorsal root ganglia had larger diameters than the negative ones. IgG antibody monospecific to GD1b may preferentially bind to large primary sensory neurons, causing sensory ataxic neuropathy.

Rabbit experimental sensory ataxic neuropathy: anti-GD1b antibody-mediated trkC downregulation of dorsal root ganglia neurons

We previously reported experimental sensory neuropathy in rabbit induced by the immunization of ganglioside GD1b. The major pathological change in diseased rabbits was degeneration of primary sensory neurons with central axons extending to the dorsal column of the spinal cord. The loss of primary sensory neurons that mediate proprioceptive sensation prompted us to investigate the expression of trkC in dorsal root ganglia (DRG) because this type of neuron is thought depend mainly on neurotrophin-3-mediated trkC signaling. Northern blotting analysis revealed markedly reduced expression of trkC in DRG of diseased rabbits in acute phase. This result together with the absence of lymphocytic infiltration in DRG of diseased rabbits at any stage suggests the anti-GD1b antibody-mediated downregulation of trkC expression could be one of the pathogenesis of this experimental sensory ataxic neuropathy.