Neural stem cells exist not only in the developing mammalian nervous system but also in the adult nervous system of all mammalian organisms, including humans. Neural stem cells can also be derived from more primitive embryonic stem cells. The location of the adult stem cells and the brain regions to which their progeny migrate in order to differentiate remain unresolved, although the number of viable locations is limited in the adult. The mechanisms that regulate endogenous stem cells are poorly understood. Potential uses of stem cells in repair include transplantation to repair missing cells and the activation of endogenous cells to provide "self-repair. " Before the full potential of neural stem cells can be realized, we need to learn what controls their proliferation, as well as the various pathways of differentiation available to their daughter cells.

https://science.sciencemag.org/content/sci/287/5457/1433.full.pdf

Mammalian neural stem cells.

Dentinal repair in the postnatal organism occurs through the activity of specialized cells, odontoblasts, that are thought to be maintained by an as yet undefined precursor population associated with pulp tissue. In this study, we isolated a clonogenic, rapidly proliferative population of cells from adult human dental pulp. These DPSCs were then compared with human bone marrow stromal cells (BMSCs), known precursors of osteoblasts. Although they share a similar immunophenotype in vitro, functional studies showed that DPSCs produced only sporadic, but densely calcified nodules, and did not form adipocytes, whereas BMSCs routinely calcified throughout the adherent cell layer with clusters of lipid-laden adipocytes. When DPSCs were transplanted into immunocompromised mice, they generated a dentin-like structure lined with human odontoblast-like cells that surrounded a pulp-like interstitial tissue. In contrast, BMSCs formed lamellar bone containing osteocytes and surface-lining osteoblasts, surrounding a fibrous vascular tissue with active hematopoiesis and adipocytes. This study isolates postnatal human DPSCs that have the ability to form a dentin/pulp-like complex.

/pdf/postnatal-human-dental-pulp-stem-cells-dpscs-in-vitro-and-in-120dw1g1sy.pdf

Postnatal human dental pulp stem cells (DPSCs) in vitro and in vivo

We report the application of single-molecule-based sequencing technology for high-throughput profiling of histone modifications in mammalian cells By obtaining over four billion bases of sequence from chromatin immunoprecipitated DNA, we generated genome-wide chromatin-state maps of mouse embryonic stem cells, neural progenitor cells and embryonic fibroblasts We find that lysine 4 and lysine 27 trimethylation effectively discriminates genes that are expressed, poised for expression, or stably repressed, and therefore reflect cell state and lineage potential Lysine 36 trimethylation marks primary coding and non-coding transcripts, facilitating gene annotation Trimethylation of lysine 9 and lysine 20 is detected at satellite, telomeric and active long-terminal repeats, and can spread into proximal unique sequences Lysine 4 and lysine 9 trimethylation marks imprinting control regions Finally, we show that chromatin state can be read in an allele-specific manner by using single nucleotide polymorphisms This study provides a framework for the application of comprehensive chromatin profiling towards characterization of diverse mammalian cell populations

/pdf/genome-wide-maps-of-chromatin-state-in-pluripotent-and-2gsrpe3xov.pdf

Genome-wide maps of chromatin state in pluripotent and lineage-committed cells

Various chronic antidepressant treatments increase adult hippocampal neurogenesis, but the functional importance of this phenomenon remains unclear. Here, using genetic and radiological methods, we show that disrupting antidepressant-induced neurogenesis blocks behavioral responses to antidepressants. Serotonin 1A receptor null mice were insensitive to the neurogenic and behavioral effects of fluoxetine, a serotonin selective reuptake inhibitor. X-irradiation of a restricted region of mouse brain containing the hippocampus prevented the neurogenic and behavioral effects of two classes of antidepressants. These findings suggest that the behavioral effects of chronic antidepressants may be mediated by the stimulation of neurogenesis in the hippocampus.

https://science.sciencemag.org/content/sci/301/5634/805.full.pdf

Requirement of Hippocampal Neurogenesis for the Behavioral Effects of Antidepressants

Astrocytes are specialized glial cells that outnumber neurons by over fivefold. They contiguously tile the entire central nervous system (CNS) and exert many essential complex functions in the healthy CNS. Astrocytes respond to all forms of CNS insults through a process referred to as reactive astrogliosis, which has become a pathological hallmark of CNS structural lesions. Substantial progress has been made recently in determining functions and mechanisms of reactive astrogliosis and in identifying roles of astrocytes in CNS disorders and pathologies. A vast molecular arsenal at the disposal of reactive astrocytes is being defined. Transgenic mouse models are dissecting specific aspects of reactive astrocytosis and glial scar formation in vivo. Astrocyte involvement in specific clinicopathological entities is being defined. It is now clear that reactive astrogliosis is not a simple all-or-none phenomenon but is a finely gradated continuum of changes that occur in context-dependent manners regulated by specific signaling events. These changes range from reversible alterations in gene expression and cell hypertrophy with preservation of cellular domains and tissue structure, to long-lasting scar formation with rearrangement of tissue structure. Increasing evidence points towards the potential of reactive astrogliosis to play either primary or contributing roles in CNS disorders via loss of normal astrocyte functions or gain of abnormal effects. This article reviews (1) astrocyte functions in healthy CNS, (2) mechanisms and functions of reactive astrogliosis and glial scar formation, and (3) ways in which reactive astrocytes may cause or contribute to specific CNS disorders and lesions.

/pdf/astrocytes-biology-and-pathology-2hq13zf0bo.pdf

Astrocytes: biology and pathology

Direct isolation of human neural and glioma stem cells from fresh tissues permits their biological study without prior culture and may capture novel aspects of their molecular phenotype in their native state. Recently, we demonstrated the ability to prospectively isolate stem cell populations from fresh human germinal matrix and glioblastoma samples, exploiting the ability of cells to bind the Epidermal Growth Factor (EGF) ligand in fluorescence-activated cell sorting (FACS). We demonstrated that FACS-isolated EGF-bound neural and glioblastoma populations encompass the sphere-forming colonies in vitro, and are capable of both self-renewal and multilineage differentiation. Here we describe in detail the purification methodology of EGF-bound (i.e., EGFR+) human neural and glioma cells with stem cell properties from fresh postmortem and surgical tissues. The ability to prospectively isolate stem cell populations using native ligand-binding ability opens new doors for understanding both normal and tumor cell biology in uncultured conditions, and is applicable for various downstream molecular sequencing studies at both population and single-cell resolution.

/pdf/facs-based-isolation-of-neural-and-glioma-stem-cell-5g73a7p8tk.pdf

FACS-based Isolation of Neural and Glioma Stem Cell Populations from Fresh Human Tissues Utilizing EGF Ligand.

Quiescent neural stem cells (NSCs) in the adult ventricular-subventricular zone (V-SVZ) have a regional identity and undergo activation to generate neurons. The domains for gliogenesis are less explored. Here we show that Platelet-Derived Growth Factor Receptor beta (PDGFRβ) is expressed by adult V-SVZ NSCs that generate olfactory bulb interneurons and glia with slow baseline kinetics. Selective deletion of PDGFRβ in adult V-SVZ NSCs leads to their release from quiescence uncovering multiple domains in the septal wall for oligodendrocyte and astrocyte formation. Unexpectedly, we identify a novel intraventricular oligodendrocyte progenitor inside the brain ventricles. Together our findings reveal different NSC spatial domains for gliogenesis in the adult V-SVZ that are largely quiescent under homeostasis and may have key functions for brain plasticity.

/pdf/release-of-stem-cells-from-quiescence-reveals-multiple-80tvxpcs19.pdf

Release of stem cells from quiescence reveals multiple gliogenic domains in the adult brain

Human organoid cultures can be used to probe secretion and drug permeability into and out of the brain The cerebrospinal fluid (CSF) is an optically clear but molecularly complex liquid that flows within the brain ventricles. It cushions the brain and delivers nutrients and signaling molecules while removing others. The CSF is produced by the choroid plexus (ChP), an understudied epithelial barrier that regulates the entry of factors from the blood into CSF and is also highly secretory. As a central hub with multiple functions, the ChP is emerging as a key contributor to normal brain physiology and disease (1). A lack of tools has limited exploration of the ChP, especially in humans. On page 159 of this issue, Pellegrini et al. (2) establish human ChP organoids, three-dimensional multicellular in vitro structures. They form compartments filled with a CSF-like fluid and exhibit functional barrier and secretion properties, resembling those in vivo. They are a powerful tool to predict drug permeability and investigate ChP secretion and cell diversity.

Exploring the source of human brain fluids.

The identification of adult brain regions harboring neural stem cells and of their continual generation of new neurons throughout life challenges traditional views of the adult brain’s germinal potential and suggests new alternatives for brain repair. Surprisingly, cells with characteristics of mature astrocytes have been shown to function as the primary precursors of new neurons in vivo. This observation goes against the generalized assumption that the rare cells with undifferentiated appearance are neural stem cells. It suggests that neural stem cells in vivo have important structural functions in addition to their role as primary progenitors. Surprisingly, neurospheres - a commonly used model of neural stem cells in culture - are not necessarily derived from the in vivo primary precursors but from transit amplifying cells. We suggest that neural stem cells, when activated to become transit amplifying cells, upregulate the expression of growth factor receptors on their surface, allowing their isolation as neurospheres.

Astrocytic nature of adult neural stem cells in vivo

Summary In the adult mouse brain, neural stem cells (NSCs) in the ventricular-subventricular zone (V-SVZ) generate neurons and glia throughout life. microRNAs are important regulators of cell states, frequently acting in a stage- or context-dependent manner. Here, miRNA profiling of FACS-purified populations identified miR-17∼92 as highly upregulated in activated NSCs and transit amplifying cells (TACs) in comparison to quiescent NSCs. Conditional deletion of miR-17∼92 in NSCs reduced stem cell proliferation both in vitro and in vivo. In contrast, in TACs, miR-17∼92 deletion caused a selective shift from neurogenic DLX2+ TACs towards oligodendrogenic OLIG2+ TACs, resulting in increased oligodendrogenesis to the corpus callosum. miR-17∼92 deletion also decreased proliferation and maturation of intraventricular oligodendrocyte progenitor cells. Together, these findings reveal stage- and cell-type-specific functions of the miR-17∼92 cluster within adult V-SVZ neural stem cell lineages.

/pdf/mir-17-92-exerts-stage-specific-effects-in-adult-v-svz-28or5gxgja.pdf

Fiona Doetsch

Papers

FACS-based Isolation of Neural and Glioma Stem Cell Populations from Fresh Human Tissues Utilizing EGF Ligand.

Release of stem cells from quiescence reveals multiple gliogenic domains in the adult brain

Exploring the source of human brain fluids.

Astrocytic nature of adult neural stem cells in vivo

miR-17∼92 exerts stage-specific effects in adult V-SVZ neural stem cell lineages