Dynamics of cell aggregation during in vitro neurogenesis by immortalized neuroectodermal progenitors

Early events of in vitro neuronal development were studied by inducing neur on formation in a neuroectodermal cell line, NE-4C/A3, derived from the emb ryonic forebrain vesicles of p53-deficient mice. Neuronal differentiation w as initiated by treating the cells with all-trans retinoic acid (RA). By th e second day of RA treatment compact cell aggregates were formed. The first signs of neuronal cell fate decision were revealed inside the aggregates. To elucidate the process of aggregate formation, the dynamics of cell clust ering and the migration of individual cells were investigated by a novel co mputer-controlled videomicroscopic system. Besides real-time observation of cell motility, the system allowed statistical analysis of large sets of da ta providing quantitative evaluation of cell locomotion during an early, cr itical phase of RA induced neuron formation. The results showed that chemoa ttractants did not play a principal role in cell aggregation. Retinoic acid , on the other hand, was found to cause a vapid decrease in the average mig ratory velocity without changing the randomness of migratory routes. The da ta indicated that aggregation was facilitated by increased cohesion upon in cident collision of randomly encountering cells. The resulting compact cell clusters provided the structural conditions for contact communication appa rently needed for the neuronal differentiation of NE-4C/A3 cells. (C) 2000 Wiley-Liss, Inc.