Adult Mammalian Forebrain Ependymal and Subependymal Cells Demonstrate Proliferative Potential, but only Subependymal Cells Have Neural Stem Cell Characteristics

Abstract

The adult derivatives of the embryonic forebrain germinal zones consist of two morphologically distinct cell layers surrounding the lateral ventricles: the ependyma and the subependyma. Cell cycle analyses have revealed that at least two proliferating populations exist in this region, one that is constitutively proliferating and one that is relatively quiescent and thought to include the endogenous adult neural stem cells. Earlier studies demonstrated that specific dissection of the region surrounding the lateral ventricles was necessary for the in vitro isolation of multipotent, self-renewing neural stem cells. However, in these studies, the ependymal layer was not physically separated from the subependymal layer to identify the specific adult laminar localization of the neural stem cells around the lateral ventricles. To determine which cellular compartment in the adult forebrain contained the neural stem cells, we isolated and cultured the ependyma separately from the subependyma and tested for the presence of neural stem cells using the in vitro neurosphere assay. We demonstrate that the ependymal cells can proliferate in vitro to form sphere-like structures. However, the ependymal cells generating spheres do not have the ability to self-renew (proliferate to form secondary spheres after dissociation) nor to produce neurons, but rather only seem to generate glial fibrillary acidic protein-positive ependymal cells when plated under differentiation conditions in culture. On the other hand, a subpopulation of subependymal cells do possess the selfrenewing and multipotential characteristics of neural stem cells. Therefore, the adult forebrain neural stem cell resides within the subependymal compartment.

Mechanism of stem cells in the central nervous system

“…Furthermore, reactive astrocytes can selectively be ablated in adult mice (Bush et al, 1999) and when lateral ventricle cells from these animals were cultured as CNS stem cells no neurospheres were generated, supporting the idea that SVZ astrocytes are CNS stem cells Chiasson et al, 1999;Laywell et al, 2000). This latter experiment indicates that GFAP expressing cells are CNS stem cells, but it does not demonstrate that GFAP expressing cells are the only CNS stem cells.…”

“…Nevertheless, the exact location of CNS stem cells was not identified and it was not until 1999 that two groups, with conceptually different methods, localized the CNS stem cells to the periventricular zone in the brain: the ependymal cell (Johansson et al, 1999b) and the SVZ astrocyte (type B cells) (Doetsch et al, 1999). These findings were shortly followed by two other reports that identified CNS stem cells that do not share all characteristics of the ependymal cell or the SVZ astrocyte (Chiasson et al, 1999;Laywell et al, 2000). At that time, it was postulated that a lineage boundary between the ependymal cells and the SVZ astrocytes exist (Barres, 1999) and some support for this assumption was demonstrated in a following report (Rietze et al, 2001).…”

Adeno-associated virus type 4 (AAV4) targets ependyma and astrocytes in the subventricular zone and RMS

“…Most studies, however, suggest that Type B astrocytes in the SVZ are the bona fide adult neural stem cell. [21][22][23][24] Type B cells functioning as neural stem cells contact the ventricular lumen with a single cilium. In either scenario of NPC lineage, AAV4 vectors would have physical access.…”

Activation of the PI3-K/Akt Pathway Mediates cGMP Enhanced-Neurogenesis in the Adult Progenitor Cells Derived from the Subventricular Zone

“…Subventricular zone cells were dissociated from normal (n ¼ 6) male Wistar rats (3 to 4 months), as previously reported (Morshead et al, 1994;Chiasson et al, 1999). The cells were plated at a density of 2 Â 10 4 cells per milliliter in DMEM-F-12 medium (Invitrogen Corporation, Carlsbad, CA, USA) containing 20 ng/mL of epidermal growth factor (EGF, R&D System, Minneapolis, MN, USA) and basic fibroblast growth factor (bFGF, R&D System, Minneapolis, MN, USA).…”