Retinoic acid induced neural differentiation in a neuroectodermal cell line immortalized by p53 deficiency.

Neuroepithelial cell lines were established from cerebral vesicles of 9-day-old mouse embryos lacking functional p53 genes (Livingstone et al: Cell 70:923-935, 1992). All-trans retinoic acid (RA) induced bulk formation of neurons both in several p53-deficient neuroepithelial cell lines and in wild-type neural cells derived from early embryonic (E9-E12) forebrain vesicles. Forty-eight-hour treatment with 10(-6) M RA was necessary and sufficient to initiate neuron formation by p53(-/-)-progenitors, but neuronal characteristics appeared with a delay of 3-4 days. The first appearance of cells with astroglial features followed that of neurons with a further delay of 4-5 days. The establishment of neuronal phenotypes involved minimally three rounds of cell cycle. Future neurons were sorted out from substrate-attached cells and were characterized by a specific rearrangement of nestin-immunoreactive filaments. The formation of neuronal phenotypes was not synchronized within the RA-treated cell populations. The data indicate that RA, which promotes the initiation of neural differentiation, cannot function as a direct regulator of cell-fate decisions made by neural progenitor cells.