Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

2.2 Neural Stem Cells Introduction
and cell therapy. For example, the neurosphere culture method has been used
extensively to study molecular and cellular mechanisms that control neuro-
genesis, differentiation and cancer proliferation [116,261], but a recent study
showed that long-term neurosphere cultures induce changed differentiation and
self-renewal capacities, and the occurrence of chromosomal instability [518].
Similarly, an earlier study by Pollard et al [401] had established that caution
should be exercised also when extrapolating in vitro adherent monolayer NS
cell culture findings to in vivo development because FGF2 induces a subset of
cell surface markers that are not found in vivo. In this study, microarray-based
expression profiling was used to identify a set of markers expressed by fetal
mouse NS cells but not ES cells and found the cell surface protein CD44 to
be differentially expressed with higher expression levels in fetal mouse-derived
NS cells. Although CD44 was expressed homogeneously by all NS cell lines
derived in this study, appreciable numbers of CD44 + cells could not be found
in the developing brain during neurogenic stages, nor in differentiating ES cell
cultures. Moreover, CD44 expression was found to be induced by FGF2 in
a subset of cells in primary culture and this effect did not appear to be re-
stricted to CD44, with many other NS cell markers found to be activated in
vitro, including Adam12, Cadherin20, Cx3cl1, EGFR, Frizzled9, Kitl, Olig1,
Olig2 and Vav3. Therefore, it was speculated that the self-renewing NS cell
state may be generated in vitro following transcriptional resetting induced by
FGF2 and the latter did not act simply to maintain and expand pre-existing
stem cells, but also impart significant changes to the transcriptional and cel-
lular phenotype [401].
Since the ability of NS cells to self-renew and differentiate into the three ma-
jor neural cell lineages make them ideal candidates to treat impaired cells
and tissues in neurodegenerative diseases, spinal cord injuries and stroke [544],
methods that can scale up their production need to be evaluated accurately.
Thus, the study by Sun et al [479] aimed at characterising the proliferative,
differentiation and passaging capacities of the two culture methods of election
for culturing NS cells, i.e. the neurosphere and adherent monolayer culture
methods. The starting material for this study was dissociated from E14 rat
cortical neuroepithelium, early enough in the development of the CNS that
proliferating NEP cells and NS cells coexist with their neuronal, neuroglial,
and glial progenitors, as well as newly post-mitotic cells (Fig 3.1). These cells
were expanded in serum-free media in the presence of the mitogenic growth fac-
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