ISOLATED RAT CORTICAL PROGENITOR CELLS ARE MAINTAINED IN DIVISION IN-VITRO BY MEMBRANE-ASSOCIATED FACTORS

Ventricular zone cells in the developing CNS undergo extensive cell di vision in vivo and under certain conditions in vitro. The culture cond itions that promote cell division have been studied to determine the r ole that contact with cell membrane associated factors plays in the pr oliferation of these cells. Progenitor cells have been taken from the ventricular zone of developing rat cerebral cortex and placed into mic rowells. Small clusters of these cells can generate large numbers of n eurons and non-neuronal progeny. In contrast, single progenitor cells largely cease division, approximately 90% acquiring neuron-likecharact eristics by 1 day in vitro. DiI-labeled, single cells from embryonic d ay 14 cortex plated onto clusters of unmarked progenitor cells have a significantly higher probability (approximately 3-fold) of maintaining a progenitor cell phenotype than if plated onto the plastic substratu m around 100 mu m away from the clusters. Contact with purified astroc ytes also promotes the progenitor cell phenotype, whereas contact with meningeal fibroblasts or balb3T3 cells promotes their differentiation . Membrane homogenates from cortical astrocytes stimulate significantl y more incorporation of BrdU by E14 cortical progenitor cells than mem brane homogenates from meningeal fibroblasts. These data indicate that the proliferation of rat cortical progenitor cells can be maintained bycell-type specific, membrane-associated factors.