Transcriptional Characterization of Glioma Neural Stem Cells Diva ...

3.2 Brain Cancer Stem Cells Introduction
the cellular level thanks to the identification of tumour-initiating cells express-
ing or not expressing Prominin as CD133 + stem cells, or more differentiated
CD133 - cells that include glioblastoma progenitor cells, respectively [121,458].
The study conducted by Singh et al [458] reports the identification and pu-
rification of a cancer stem cell exclusively isolated within the cell fraction
expressing the neural stem cell surface marker CD133, from different pheno-
types of human brain tumours. Higher-grade gliomas showed an increased
self-renewal capacity with respect to lower-grade gliomas and, importantly,
the CD133 + cells could differentiate in culture into tumour cells that pheno-
typically resembled the tumour from the patient. Neurosphere assays were
used to functionally characterize the tumour cell population and identified the
CD133 + cell as representing the minority of the tumour cell population. This
cell lacked the expression of neural differentiation markers, was necessary for
the proliferation and self-renewal of the tumour in culture, and was capable
of differentiating in vitro into cell phenotypes identical to the tumour in situ.
Since the identified cancer stem cell markers CD133 and Nestin were also iden-
tified as defining normal NS cells, it was suggested that brain tumours can be
generated from cancer stem cells that share a very similar phenotype as normal
NS cells. Such identification of a brain tumour cancer stem cell, set up the
research scene for the following investigations of the tumourigenic process in
the CNS.
In the study by Singh et al, cultures from 14 solid primary pediatric brain
tumours were set to favour stem cell growth, resulting in all tumours grow-
ing within the first 48 hours as clonally derived neurosphere-like clusters, the
"tumour spheres", that continued to proliferate and expand the tumour cell
culture over time. All primary tumour spheres were assessed for ability to
form secondary tumour spheres upon re-plating, and all successfully exhibited
self-renewal abilities. The frequency of secondary tumour sphere generation
correlated with the tumour’s tumour clinical aggressiveness and varied accord-
ing to tumour pathological subtype. Both primary and secondary tumour
spheres retained the expression of the NS cell markers Nestin and CD133,
failing instead to express the neural differentiation marker of election for as-
trocytes, GFAP, and neurons, TUBB3 [458]. In neurosphere conditions, in
fact, brain tumour cells express Nestin and CD133 but also markers of neural
precursors such as Sox2, Notch and Jagged-1 [122]. By inducing differentiation
in culture, Singh et al observed that the dissociated tumour spheres preferen-
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