Glial Commitment of Mesencephalic Neural Precursor Cells Expanded as Neurospheres Precludes Their Engagement in Niche-Dependent Dopaminergic Neurogenesis
Baizabal, JM and Cano-Martinez, A and Valencia, C and Santa-Olalla, J and Young, KM and Rietze, RL and Bartlett, PF and Covarrubias, L, Glial Commitment of Mesencephalic Neural Precursor Cells Expanded as Neurospheres Precludes Their Engagement in Niche-Dependent Dopaminergic Neurogenesis, Stem Cells and Development, 21, (7) pp. 1047-1058. ISSN 1547-3287 (2012) [Refereed Article]
Neural precursor cells (NPCs) with high proliferative potential are commonly expanded in vitro as neurospheres.
As a population, neurosphere cells show long-term self-renewal capacity and multipotentiality in vitro.
These features have led to the assumption that neurosphere cells represent an expansion of the endogenous
NPCs residing within the embryonic and adult brain. If this is the case, in principle, bona-fide expansion of
endogenous NPCs should not significantly affect their capacity to respond to their original niche of differentiation.
To address this issue, we generated primary neurospheres from the dopaminergic niche of the ventral
mesencephalon and then transplanted these cells to their original niche within mesencephalic explant cultures.
Primary neurosphere cells showed poor capacity to generate dopaminergic neurons in the mesencephalic niche
of dopaminergic neurogenesis. Instead, most primary neurosphere cells showed glial commitment as they
differentiated into astrocytes in an exclusively neurogenic niche. Subculture of primary cells demonstrated that
the neurosphere assay does not amplify niche-responsive dopaminergic progenitors. Further, neurospheres
cells were largely unable to acquire the endogenous positional identity within the Nkx6.1+, Nkx2.2+, and Pax7+
domains of mesencephalic explants. Finally, we demonstrate that our observations are not specific for embryonic
mesencephalic cells, as NPCs in the adult subventricular zone also showed an intrinsic fate switch from neuronal
to glial potential upon neurosphere amplification. Our data suggest that neurosphere formation does not expand
the endogenous neurogenic NPCs but rather promotes amplification of gliogenic precursors that do not respond
to niche-derived signals of cellular specification and differentiation.