Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

2.2 Neural Stem Cells Introduction
a platform to study the molecular events involved in the transitions between
precursors [400]. Based on the view that neural differentiation of ES cells in
vitro does recapitulate neural development in vivo, several studies isolated an
RC2 immunoreactive radial glia-like cell as the transient neural progenitor in-
volved in the transition from NEP cells to neuronal and glial subtypes (Fig
2.6) [302,399].
Figure 2.6: Diagram to visualise the progressive lineage restriction of ES cells
differentiating toward the neural phenotype in neurospheres, showing the transition
of NEP cells to RC2 immunoreactive radial glia-like cells. Adapted from Pollard et
al 2007 [400].
Likely due to paracrine LIF signaling, many ES cell neural differentiation pro-
tocols have the drawback of fostering the generation of non-homogeneous cul-
tures that include contaminating populations of non-neural cells and residual
ES cells [400]. This effect can be overcome by adopting a "lineage selection"
strategy, in which a reporter gene or drug resistance gene is expressed as a
transgene 30 under cell type specific promoter elements, such as the Sox1-GFP
reporter construct for the isolation of NEP cells [32]. ES cell-derived cultures
engineered to express the Sox1-GFP reporter are initially enriched in Sox1 +
NEP cells but quickly differentiate to neurons and glia due to the niche environ-
ment recreated in neurospheres that mimics in vivo developmental cues [400].
In order to isolate cells capable of undergoing symmetrical stem cell divisions
without differentiation, a niche-independent protocol was devised by Conti et
al [107] that uses adherent conditions to ensure homogeneity of the stem cell
population bypassing the formation of neurospheres. The unique characteris-
tic of this protocol is the use of EGF in attached monolayer culture, which
30 A gene that does not belong to the wild type genome sequence but can be introduced
from an another organism naturally or by means of genetic engineering.
44