Mitosis and population density in cultures of embryonic chick and mouse fibroblasts

Abstract

Summary Mitosis at varying population densities of secondary embryonic chick and mouse fibroblasts was studied in short-term monolayer cultures, using Colcemid. A presumed feeder effect was observed for the growth of mouse fibroblasts, suggested by an optimum density of about 1000 cells/mm 2 for mitotic rate in 48-h cultures. This effect was not observed in the cultures of chick fibroblasts. Apart from the presumed feeder effect in mouse cells, the metaphase index of both chick and mouse fibroblasts declined with increasing cell population density at the time of observation, particularly over the range of densities around confluence. The decline at densities beyond 3000 cells/mm 2 was small for chick fibroblasts and negligible for mouse fibroblasts. Density-inhibition of mitosis occurred independently of stirring a common medium over sparse and dense populations in the same culture; in these circumstances it was not however detected after only 24 h of culture. There was a depressing effect of age in culture on mitosis, over and above the effect of population density at the time of fixation. It is suggested that this may work through the depletion of nutrients or the accumulation of inhibitory substances in the medium; there was some evidence for this hypothesis in the case of the chick cells.