No abstract

Microglia are increasingly implicated as a source of non-neural regulation of postnatal neurogenesis and neuronal development. To evaluate better the contributions of microglia to neural stem cells (NSCs) of the subventricular neuraxis, we employed an adherent culture system that models the continuing proliferation and differentiation of the dissociated neuropoietic subventricular tissues. In this model, neuropoietic cells retain the ability to self-renew and form multipotent neurospheres, but progressively lose the ability to generate committed neuroblasts with continued culture. Neurogenesis in highly expanded NSCs can be rescued by coculture with microglial cells or microglia-conditioned medium, indicating that microglia provide secreted factor(s) essential for neurogenesis, but not NSC maintenance, self-renewal, or propagation. Our findings suggest an instructive role for microglial cells in contributing to postnatal neurogenesis in the largest neurogenic niche of the mammalian brain.

The tyrosine kinase c-Met promotes the formation and malignant progression of multiple cancers. It is well known that c-Met hyperactivation increases tumorigenicity and tumor cell resistance to DNA damaging agents, properties associated with tumor-initiating stem cells. However, a link between c-Met signaling and the formation and/or maintenance of neoplastic stem cells has not been previously identified. Here, we show that c-Met is activated and functional in glioblastoma (GBM) neurospheres enriched for glioblastoma tumorinitiating stem cells and that c-Met expression/function correlates with stem cell marker expression and the neoplastic stem cell phenotype in glioblastoma neurospheres and clinical glioblastoma specimens. c-Met activation was found to induce the expression of reprogramming transcription factors (RFs) known to support embryonic stem cells and induce differentiated cells to form pluripotent stem (iPS) cells, and c-Met activation counteracted the effects of forced differentiation in glioblastoma neurospheres. Expression of the reprogramming transcription factor Nanog by glioblastoma cells is shown to mediate the ability of c-Met to induce the stem cell characteristics of neurosphere formation and neurosphere cell self-renewal. These findings show that c-Met enhances the population of glioblastoma stem cells (GBM SCs) via a mechanism requiring Nanog and potentially other c-Met-responsive reprogramming transcription factors.cancer stem cell | hepatocyte growth factor | Sox2 | Oct4 | Klf4 G lioblastomas (GBMs) are heterogeneous aggressive neoplasms containing neoplastic stem-like cells (1). These cells commonly referred to as glioblastoma stem cells (GBM SCs), exhibit the capacity for unlimited growth as multicellular spheres in defined medium, multilineage differentiation, and efficient tumor initiation in immune-deficient animals. GBM SCs are currently believed to play a leading role in therapeutic resistance and tumor recurrence (2). Defining the origin(s) of GBM SCs and the biochemical/molecular pathways that support the stem-like tumor-initiating phenotype is of major importance.Transcription factors such as Sox2, c-Myc, Klf4, Oct4, and Nanog have an essential role in sustaining the growth and selfrenewal of embryonic stem (ES) cells. Introducing these transcription factors into mouse and human differentiated somatic cells results in their reprogramming into pluripotent ES-like cells called induced pluripotent stem (iPS) cells (3). Remarkable similarities exist between stem cell reprogramming and oncogenesis. Both processes are supported by alterations in the expression/function of similar collaborating genes perpetuating subpopulations of cells capable of indefinite self-renewal (4). Reprogramming transcription factors (RFs) display varying degrees of oncogenic potential, are overexpressed in human cancers, and their expression levels have been correlated with malignant progression and poor prognosis (5, 6). Loss of tumor suppressors such as p53 enhances the efficiency of iPS cell generation b...

The modern concept of neurogenesis in the adult brain is predicated on the premise that multipotent glial cells give rise to new neurons throughout life. Although extensive evidence exists indicating that this is the case, the transition from glial to neuronal phenotype remains poorly understood. A unique monolayer cellculture system was developed to induce, expose, and recapitulate the entire developmental series of events of subventricular zone (SVZ) neurogenesis. We show here, using immunophentoypic, ultrastructural, electrophysiological, and time-lapse analyses, that SVZ-derived glial fibrillary acidic protein low ͞A2B5 ؉ ͞nestin ؉ candidate founder cells undergo metamorphosis to eventually generate large numbers of fully differentiated interneuron phenotypes. A model of postnatal neurogenesis is considered in light of known embryonic events and reveals a limited developmental potential of SVZ stem͞progenitor cells, whereby ancestral cells in both embryonic and postnatal͞adult settings give rise to glia and GABAergic interneurons.adult stem cells ͉ electrophysiology ͉ in vitro ͉ neurogenesis ͉ subventricular zone A ttempts to trace the cellular source of neurogenesis in the adult CNS have recently led to the surprising conclusion that dedicated glial cells give rise to new neurons throughout life (1-5). Even though neurons and glia are both derived from the embryonic neuroepithelium, sharing common signaling pathways and downstream transcription factors during development (6), it is difficult to imagine how one major cell class in the adult brain can transpose into the other. Postnatal neurogenesis in the subventricular zone (SVZ) of rodents proceeds as a characteristic series of events, where multipotent glial cells (referred to as type-B cells) can divide to form colonies of neuroblasts (type-A cells) through a transit-amplifying cell population (type-C cells) (7). Newborn neuroblasts migrate from the SVZ through the rostral migratory stream and mature to GABAergic granule cells and periglomerular cells, which, 3-4 weeks after generation, integrate as inhibitory interneurons into the olfactory bulb of rodents (8-10). Certain features, such as nestinand glial-fibrillary acidic protein (GFAP) expression, are ascribed to the founder cells of postnatal neurogenesis (3,(11)(12)(13)(14), but their distinctive antigenic and functional profiles remain elusive. Traditional approaches for the isolation and characterization of persistent neurogenesis have relied on the in vitro neurosphere (NS) assay (15, 16) or on post hoc identification, depending on the incorporation of BrdUrd and͞or retroviral constructs to label precursors during cell division. However, neither of these methods affords the recognition of the dynamic processes involved in the maturation of individual cells en route from stem cells to fully differentiated neural phenotypes.Here, we present an alternative culture model that closely recapitulates in vivo postnatal͞adult SVZ neurogenesis, allowing us to monitor the entire sequence of hierarchical eve...