Is neurogenesis in embryos mechanistically similar to that in the adult?
How related is neurogenesis in embryos to that occurring in the adult? Several points of comparison are worth discussing, based on what is known about neurogenesis in embryos, although the answer to this question is obviously a problem for the future. One point is that the source of new neurons in the adult is unlikely to be a direct counterpart to the neuroepithelial cells that generate neurons in the embryo. The obvious requirement that stem cells divide makes such terminally differentiated cells such as neurons or oligodendrocytes unlikely sources of neural stem cells. Cell types retained within the neuroepithelium of the adult nervous system, such as ependyma or the so-called radial glia cells, are more likely sources based on their similarity to embryonic neuroepithelial cells from which they are closely derived (Alvarez-Buylla et al., 2001; Tamamaki et al., 2001). Indeed, as direct remnants of the embryonic neuroepithelium, these cells conceivably retain or continue to respond to
