In the vertebrate CNS, the neuroepithelium gives rise to most of the neuronal as well as the macroglial cells found in mature tissue. The mechanism by which the neuroepithelial cells first differentiate and follow the different cell lineages is largely unknown, nor is it clear when the decision for differentiation is made.
As with neurogenesis, most of the current understanding of the process of gliogenesis derives from the study of a relatively simple nervous system, such as the optic nerve. The optic nerve develops from the optic stalk, which is an extension of the original neuroepithelium (Fig. 8). The neuroepithelial cells that form this optic stalk give rise only to glial cells (astrocytes and oligodendroglia) and not to neurons. Neurobiol-ogists have used this characteristic of the cell lineage systems of the optic stalk to study the pattern of gliogenesis.
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