Departamento de Genética del Desarrollo y Fisiología Molecular, Instituto de Biotecnología, Universidad Nacional Autónoma de México, Cuernavaca, México.
Stem Cells Dev. 2012 May 1;21(7):1047-58. doi: 10.1089/scd.2011.0241. Epub 2011 Jul 6.
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.
神经前体细胞（NPCs）具有高增殖潜能，通常在体外作为神经球进行扩增。作为一个群体，神经球细胞在体外表现出长期自我更新能力和多能性。这些特征导致人们假设神经球细胞代表了内源性 NPCs 的扩增，这些 NPCs存在于胚胎和成年大脑中。如果是这样，原则上，内源性 NPCs 的真正扩增不应显著影响它们对其原始分化龛的反应能力。为了解决这个问题，我们从腹侧中脑的多巴胺能龛中生成原代神经球，然后将这些细胞移植到中脑外植体培养物的原始龛中。原代神经球细胞在多巴胺能神经发生的中脑龛中产生多巴胺能神经元的能力很差。相反，大多数原代神经球细胞在专门的神经发生龛中分化为星形胶质细胞时表现出胶质细胞的定向分化。原代细胞的亚培养表明，神经球测定法不会扩增对龛有反应的多巴胺能祖细胞。此外，神经球细胞在很大程度上无法在中脑外植体的 Nkx6.1(+)、Nkx2.2(+)和 Pax7(+) 区域内获得内源性位置身份。最后，我们证明我们的观察结果不仅限于胚胎中脑细胞，因为成年侧脑室下区的 NPCs 在神经球扩增时也表现出从神经元到神经胶质潜能的内在命运转变。我们的数据表明，神经球形成不会扩增内源性神经发生 NPCs，而是促进对龛衍生的细胞特化和分化信号无反应的神经胶质前体的扩增。
