Differentiation Mechanism of Embryonic Stem Cells into Neural Stem Cells

神经干细胞通过在星形胶质细胞条件培养液(ACM)中自由漂浮条件下形成神经干细胞球(NSSS)从胚胎干细胞分化而来。在随后的神经干细胞在含有成纤维细胞生长因子-2的粘附性基质上培养的过程中，神经干细胞被诱导迁移到基质上，导致细胞数量的扩大。此外，通过将培养液从NeurobasicB-27改为ACM，几乎所有这些细胞都可以分化为功能神经元，这表明ES细胞来源的神经干细胞向神经元分化需要ACM中存在的一些指导性因子。此外，这些来自ES细胞的神经干细胞可以在没有任何额外体液因素的情况下，通过从培养液中提取FGF-2来几乎完全分化为星形胶质细胞。与神经发生不同，这种星形细胞发生不需要任何额外的指导。我们的结果表明，沿着星形胶质细胞谱系分化是ES细胞来源的神经干细胞的默认状态。

Neural stem cells differentiate from embryonic stem (ES) cells via formation of neural stem spheres (NSSs) under free-floating conditions in astrocyte-conditioned medium (ACM). During subsequent culture of the NSSs on an adhesive substrate with fibroblast growth factor (FGF)-2, the neural stem cells are induced to migrate onto the substrate, resulting in an expansion of the cell number. Furthermore, almost all these cells can be differentiated into functional neurons by changing the medium from Neurobasal B-27 to ACM, suggesting that differentiation of the ES-cell-derived neural stem cells into neurons requires some instructive factors present in ACM. In addition, these ES-cell-derived neural stem cells can be differentiated almost exclusively into astrocytes by withdrawing FGF-2 from the medium without any additional humoral factors. This astrocytegenesis does not require any additional instructions in contrast to neurogenesis. Our results indicate that differentiation along the astrocyte lineage is a default state of ES-cell-derived neural stem cells