Samuel Weiss

NEURAL STEM CELLS IN THE ADULT MAMMALIAN FOREBRAIN : A RELATIVELY QUIESCENT SUBPOPULATION OF SUBEPENDYMAL CELLS

Dissection of the subependyma from the lateral ventricle of the adult mouse forebrain is necessary and sufficient for the in vitro formation of clonally derived spheres of cells that exhibit stem cell properties such as self-maintenance and the generation of a large number of progeny comprising the major cell types found in the central nervous system. Killing the constitutively proliferating cells of the subependyma in vivo has no effect on the number of stem cells isolated in vitro and induces a complete repopulation of the subependyma in vivo by relatively quiescent stem cells found within the subependyma. Depleting the relatively quiescent cell population within the subependyma in vivo results in a corresponding decrease in spheres formed in vitro and in the final number of constitutively proliferating cells in vivo, suggesting that a relatively quiescent subependymal cell is the in vivo source of neural stem cells.

bFGF regulates the proliferative fate of unipotent (neuronal) and bipotent (neuronal/astroglial) EGF-generated CNS progenitor cells

In cultures of embryonic and adult mouse striatum, we previously demonstrated that EGF induces the proliferation of putative stem cells, which give rise to spheres of undifferentiated cells that can generate neurons and astrocytes. We report here that the spheres of undifferentiated cells contain mRNA and protein for the FGF receptor (FGFR1). Indirect immunocytochemistry demonstrated that many of the cells within the EGF-generated spheres were immunoreactive for FGFR1. Exogenous application of bFGF to the EGF-generated cells induced the proliferation of two progenitor cell types. The first, a bipotent progenitor cell, gave rise to cells with the antigenic and morphological properties of neurons and astrocytes; the other gave rise to cells with neuronal characteristics only. bFGF-generated cells with neuronal morphology exhibited electrophysiological properties indicative of immature central neurons. These results support the hypothesis that sequential actions of growth factors play a role in regulating the generation of neurons and astrocytes in the developing CNS.

Is there a neural stem cell in the mammalian forebrain

Neural precursor cells have been of interest historically as the building blocks of the embryonic CNS and, most recently, as substrates for restorative neurological approaches. The majority of previous in vitro studies of the regulation of neural-cell proliferation by polypeptide growth factors, and in vivo studies of neural lineage, argue for the presence of precursors with limited proliferative or lineage potential in the mammalian CNS. This is in contrast to renewable tissues, such as the blood or immune system, skin epithelium and epithelium of the small intestinal crypts, which contain specialized, self-renewing cells known as stem cells. However, recent in vitro and in vivo studies from our and other laboratories lead us to conclude that neural stem cells, with self-renewal and multilineage potential, are present in the embryonic through to adult mammalian forebrain.

Transformation by the ( R )-enantiomer of 2-hydroxyglutarate linked to EGLN activation

The identification of succinate dehydrogenase (SDH), fumarate hydratase (FH) and isocitrate dehydrogenase (IDH) mutations in human cancers has rekindled the idea that altered cellular metabolism can transform cells. Inactivating SDH and FH mutations cause the accumulation of succinate and fumarate, respectively, which can inhibit 2-oxoglutarate (2-OG)-dependent enzymes, including the EGLN prolyl 4-hydroxylases that mark the hypoxia inducible factor (HIF) transcription factor for polyubiquitylation and proteasomal degradation. Inappropriate HIF activation is suspected of contributing to the pathogenesis of SDH-defective and FH-defective tumours but can suppress tumour growth in some other contexts. IDH1 and IDH2, which catalyse the interconversion of isocitrate and 2-OG, are frequently mutated in human brain tumours and leukaemias. The resulting mutants have the neomorphic ability to convert 2-OG to the (R)-enantiomer of 2-hydroxyglutarate ((R)-2HG). Here we show that (R)-2HG, but not (S)-2HG, stimulates EGLN activity, leading to diminished HIF levels, which enhances the proliferation and soft agar growth of human astrocytes. These findings define an enantiomer-specific mechanism by which the (R)-2HG that accumulates in IDH mutant brain tumours promotes transformation and provide a justification for exploring EGLN inhibition as a potential treatment strategy.

Aging Results in Reduced Epidermal Growth Factor Receptor Signaling, Diminished Olfactory Neurogenesis, and Deficits in Fine Olfactory Discrimination

Previous studies demonstrating olfactory interneuron involvement in olfactory discrimination and decreased proliferation in the forebrain subventricular zone with age led us to ask whether olfactory neurogenesis and, consequently, olfactory discrimination were impaired in aged mice. Pulse labeling showed that aged mice (24 months of age) had fewer new interneurons in the olfactory bulb than did young adult (2 months of age) mice. However, the aged mice had more olfactory interneurons in total than their younger counterparts. Aged mice exhibited no differences from young adult mice in their ability to discriminate between two discrete odors but were significantly poorer at performing discriminations between similar odors (fine olfactory discrimination). Leukemia inhibitory factor receptor heterozygote mice, which have less neurogenesis and fewer olfactory interneurons than their wild-type counterparts, performed more poorly at fine olfactory discrimination than the wild types, suggesting that olfactory neurogenesis, rather than the total number of interneurons, was responsible for fine olfactory discrimination. Immunohistochemistry and Western blot analyses revealed a selective reduction in expression levels of epidermal growth factor (EGF) receptor (EGFR) signaling elements in the aged forebrain subventricular zone. Waved-1 mutant mice, which express reduced quantities of transforming growth factor-α, the predominant EGFR ligand in adulthood, phenocopy aged mice in olfactory neurogenesis and performance on fine olfactory discrimination tasks. These results suggest that the impairment in fine olfactory discrimination with age may result from a reduction in EGF-dependent olfactory neurogenesis.

Male pheromone–stimulated neurogenesis in the adult female brain: possible role in mating behavior.

The regulation of female reproductive behaviors may involve memories of male pheromone signatures, formed in part by neural circuitry involving the olfactory bulb and hippocampus. These neural structures are the principal sites of adult neurogenesis; however, previous studies point to their independent regulation by sensory and physiological stimuli. Here we report that the pheromones of dominant (but not subordinate) males stimulate neuronal production in both the olfactory bulb and hippocampus of female mice, which are independently mediated by prolactin and luteinizing hormone, respectively. Neurogenesis induced by dominant-male pheromones correlates with a female preference for dominant males over subordinate males, whereas blocking neurogenesis with the mitotic inhibitor cytosine arabinoside eliminated this preference. These results suggest that male pheromones are involved in regulating neurogenesis in both the olfactory bulb and hippocampus, which may be important for female reproductive success.

Concurrent CIC mutations, IDH mutations, and 1p/19q loss distinguish oligodendrogliomas from other cancers

Oligodendroglioma is characterized by unique clinical, pathological, and genetic features. Recurrent losses of chromosomes 1p and 19q are strongly associated with this brain cancer but knowledge of the identity and function of the genes affected by these alterations is limited. We performed exome sequencing on a discovery set of 16 oligodendrogliomas with 1p/19q co‐deletion to identify new molecular features at base‐pair resolution. As anticipated, there was a high rate of IDH mutations: all cases had mutations in either IDH1 (14/16) or IDH2 (2/16). In addition, we discovered somatic mutations and insertions/deletions in the CIC gene on chromosome 19q13.2 in 13/16 tumours. These discovery set mutations were validated by deep sequencing of 13 additional tumours, which revealed seven others with CIC mutations, thus bringing the overall mutation rate in oligodendrogliomas in this study to 20/29 (69%). In contrast, deep sequencing of astrocytomas and oligoastrocytomas without 1p/19q loss revealed that CIC alterations were otherwise rare (1/60; 2%). Of the 21 non‐synonymous somatic mutations in 20 CIC‐mutant oligodendrogliomas, nine were in exon 5 within an annotated DNA‐interacting domain and three were in exon 20 within an annotated protein‐interacting domain. The remaining nine were found in other exons and frequently included truncations. CIC mutations were highly associated with oligodendroglioma histology, 1p/19q co‐deletion, and IDH1/2 mutation (p < 0.001). Although we observed no differences in the clinical outcomes of CIC mutant versus wild‐type tumours, in a background of 1p/19q co‐deletion, hemizygous CIC mutations are likely important. We hypothesize that the mutant CIC on the single retained 19q allele is linked to the pathogenesis of oligodendrogliomas with IDH mutation. Our detailed study of genetic aberrations in oligodendroglioma suggests a functional interaction between CIC mutation, IDH1/2 mutation, and 1p/19q co‐deletion. Copyright

Mitotically active cells that generate neurons and astrocytes are present in multiple regions of the adult mouse hippocampus

Previous studies of the adult hippocampus of rodents and primates have reported neuro‐ and gliogenesis restricted to the region of the dentate gyrus. In the present study, by employing a prolonged bromodeoxyuridine (BrdU) labeling protocol that attempts to account for cytokinetic changes as an animal ages, we have identified mitotically active cells in multiple regions of the hippocampus, especially in Ammons horn, of the adult mouse. Immediately following the labeling period, the BrdU‐labeled cells did not express known markers for neurons and astrocytes. Subsequent analysis at 3–24 weeks after labeling demonstrated BrdU‐labeled neurons and glia in these regions of the hippocampus. Although neuro‐ and gliogenesis in the adult mammalian hippocampus have been reported previously, these results demonstrate that the phenomenon is not limited to the region of the dentate gyrus, but rather extends into Ammons horn. Furthermore, it suggests that ongoing cell production, albeit discrete and limited in nature, may be widespread in the adult mammalian central nervous system. J. Comp. Neurol. 424:397–408, 2000.

White Matter Plasticity and Enhanced Remyelination in the Maternal CNS

Myelination, the process in which oligodendrocytes coat CNS axons with a myelin sheath, represents an important but poorly understood form of neural plasticity that may be sexually dimorphic in the adult CNS. Remission of multiple sclerosis during pregnancy led us to hypothesize that remyelination is enhanced in the maternal brain. Here we report an increase in the generation of myelin-forming oligodendrocytes and in the number of myelinated axons in the maternal murine CNS. Remarkably, pregnant mice have an enhanced ability to remyelinate white matter lesions. The hormone prolactin regulates oligodendrocyte precursor proliferation and mimics the regenerative effects of pregnancy. This suggests that maternal white matter plasticity imparts a striking ability to repair demyelination and identifies prolactin as a potential therapeutic agent.

Identity crisis for adult periventricular neural stem cells: subventricular zone astrocytes, ependymal cells or both?

A population of neural stem cells (NSCs) resides adjacent to the lateral ventricles in the adult mammalian brain. Despite knowledge of their existence since the early 1990s, their identity remains controversial, with evidence suggesting that they may be ependymal cells, glial fibrillary acidic protein (GFAP)-expressing subventricular zone (SVZ) cells or several distinct NSC populations. This issue has major implications for the therapeutic use of NSCs as well as for the study and treatment of brain cancers. Recent studies have both shed light on the issue and added to the controversy.