Consequences of parental exposure to serum-free medium for progeny cell division

Proliferating serum-dependent 3T3 cells prolong their intermitotic time by 9-10 h after exposure to serum-free medium for only 1 h. This delay was only observed in cells younger than 4 h, i.e. cells in the postmitotic G1 phase (G1pm), as defined by time elapsed since previous mitosis. These data confirm earlier findings that cells are very sensitive to growth factor or serum depletion during the first part of G1 and that only a short exposure to serum-free medium is sufficient for the cells to leave the cell cycle. However, such cells that have delayed their first cell cycle in response to a short exposure to serum-free medium in early G1 exhibit a reduced capacity to delay the subsequent cycle in response to a repeated exposure to serum-free medium. In contrast cells older than 4 h that are exposed for short periods to serum-free medium undergo cell division on schedule, but delay the subsequent cell cycle by several hours. This delay of the progeny cycle is mainly ascribable to the postmitotic part of G1 (G1pm). These data suggest that short exposures to serum-free medium exert an indirect effect on the progeny cell cycle and demonstrate that cycle times are not necessarily determined de novo in the lifetime of every cell, but may be influenced by events in the preceding cycle.