Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

2.2 Neural Stem Cells Introduction
ensuing. Recently it was reported that different types of human astro-
cytes may express distinct GFAP isoforms: adult SVZ astroglial cells
express GFAPδ, while most other astrocytes, including the derivative as-
trocytes of the human NS cells developed in the protocol by Sun et al,
express GFAPα [432].
In the protocol described by Sun et al [481], during the first four weeks after
cells are plated, primary human cells attach on laminin substrate within 24
hours and start to proliferate in the presence of both EGF and FGF2, with
no extended cell proliferation observed in medium containing only one of the
two growth factors and the subsequent impossibility of establishing NS cell
lines successfully. In addition to EGF and FGF2, the laminin substrate is
important for efficient human NS cell derivation, since primary cells grown
on gelatin coated or uncoated dishes easily detach and tend to form neuro-
spheres resulting in slower proliferation, as described in the study by Conti
et al [107]. The laminin substrate was also found to be optimal for human
NS cell propagation, indicating that laminin may play important roles in reg-
ulating neural cell behaviour [481]. Finally, although the human fetal-derived
NS cells exhibited some features of radial glia, the artificial nature of culture
environments may result in unique cell populations in vitro, which may indi-
cate, in turn, that NS cells do not have direct in vivo counterparts. In fact, as
a further consideration, the combination of transcription factor expression in
mouse NS cells is not routinely observed during normal development [403,481].
In order to shed the light on the nature of NS cells and their relationship
to endogenous cell types, Pollard et al [403] have investigated whether cells
capable of giving rise to NS cell cultures are restricted to developmental stages
or may also be present in the mouse adult brain. Although both FGF2 and
EGF were necessary for the derivation in culture of NS cells from adult mouse
forebrain (containing the adult SVZ), once established, the stem cell lines could
be maintained in added EGF alone. As already seen in mouse ES cell-derived
NS cell cultures, the absence of EGF causes the majority of the NS cells to die
of caspase 3-activated apoptosis and the rest to start differentiating towards
the neuronal lineage, although never reaching the fully mature phenotype (Fig
2.9). On the contrary, withdrawal of FGF2 did not result in any striking
change in NS cell morphology or behaviour, with the exception of a slightly
lower doubling time for EGF-only grown colonies possibly due to a higher
cell death, although more detailed analysis are required [403]. For complete
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