神経幹細胞の性質と移植後の分化動態について

Generation of neurons in the mammalian central nervous system (CNS) is believed to end by early postnatal life. However, neurogenesis has been demonstrated in different regions of both the developing and mature CNS. In such areas, neural stem cells and progenitor cells have been isolated using trophic factors. When the cells are cultured in a chemically defined, serum-free medium with epidermal growth factor (EGF) or basic fibroblast growth factor (FGF-2), they proliferate as cellular clusters floating in the medium (‘neurospheres’). In vitro, clonal analyses indicate that such cells can individually generate neurons, astrocytes and oligodendrocytes. Cells from expanded neurosphere cultures are grafted into valious regions of CNS, including hypothalamus, hippocampus, medulla oblongata and subventricular zone. FGF-2 and EGF-responsive cells differentitate predominantly give rise to glial cells. Some of FGF-2-responsive cells transplanted into neurogenic regions of mouse brain differentiate into region-specific neurons. The characters and relative advantages of these cells for cell replacement therapy are discussed.