Cell-cell contact promotes DNA synthesis in retinal glia but not in fibroblasts

Contact among retinal glial cells in monolayer cultures of intermediate density stimulated DNA synthesis. The stimulation occurred in passaged cultures lacking neuronal elements and is, therefore, the first demonstration of growth promotion by contact among cells of the same apparent type. In contrast, low levels of association among dermal fibroblasts in cultures of similar density had no stimulatory effect. However, as few as three cellular contacts depressed fibroblast DNA synthesis. This latter observation suggests that the density dependent suppression of fibroblast proliferation observed in confluent cultures begins to be expressed at subconfluent cell densities.