Résumé
The rapidly cycling neuroepithelial cells, located in the ventricular and subventricular zones of the neural tube, give rise to most of the neurons and macroglial cells, astrocytes and oligodendrocytes, in the vertebrate central nervous system (CNS). In most CNS areas, neurons are the first to develop, followed by astrocytes, and at later stages by oligodendrocytes. An important issue in the study of early CNS development is to understand the lineage relationships of the various CNS cell types and the mechanisms by which these lineages segregate and differentiate. One aspect of this question is to define when and how precursor cells become committed to a specific differentiation pathway. For example, neuroepithelial cells could initially all be endowed with equivalent differentiation capabilities. The specification of these multipotential precursor cells towards a defined phenotype could be controlled by instructive and selective cues arising progressively from their immediate environment. Alternatively, neuroepithelial progenitors could be, from early stages in nervous system ontogeny, already segregated into subpopulations with differing potentialities. In this case, environmental cues would be less critical than intrinsic developmental programs in regulating phenotypic choices.