Developmental Potentials of Early Telencephalic Neuroepithelial Cells: A Study with Microexplant Culture

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Abstract
To gain a better understanding of how neuron generation begins in the telencephalon, we analyzed the developmental potentials of neuroepithelial cells (NE cells) using a microexplant culture system. By the patterns of neuron generation and cell spreading on fibronectin (FN) in vitro, we recognized at least three different types of NE cells in the early (E9 to E10.5) telencephalon of mice. Although there was no transition from one growth pattern to another in vitro, these patterns were found to represent distinct stage-dependent profiles of the NE cells. (i) The youngest type of NE cells spread well and formed flat cell sheets on FN, but generated no neurons at all. (ii) An intermediate type showed extensive spreading on FN and generated a small number of neurons only early in culture. (iii) In contrast, NE cells at the most advanced stage examined formed compact cell sheets independent of FN and showed continuous neuron generation. These results indicate that telencephalic NE cells at the beginning of neurogenesis do not have a potential to make all cerebral neurons simultaneously. Our findings suggest that, during the period of E9 to E10.5, NE cells first acquire a potential to make the neurons produced before E12.5 and the NE cells then become capable of generating the neurons formed later under the influence of environmental factors.