Proliferative behavior of the murine cerebral wall in tissue culture: cell cycle kinetics and checkpoints

Cerebral wall from embryonic day 13 mice was cultured in a three-dimensional collagen matrix in defined, serum-free medium. The cerebral wall retained its normal architecture, including the radial glial fiber system, for up to 19 h in culture. The cell cycle was initially blocked at the S/G2/M and the G1/S phase transitions, resulting in a transient synchronization of the proliferative cells. The transient blockades correspond, we suggest, to the G2 checkpoint and G1 restriction point, adaptive mechanisms of normal proliferative cells. The blocks were relieved within a few hours of explantation with restoration of the interkinetic nuclear migration and flow of cells through the cycle phases. The duration of the reestablished cell cycle and those of G1, S, and combined G2-M phases were estimated to be 19.2, 6.3-8.3, 8.8, and 2.0-4.0 h, respectively. The leaving (Q) fraction of the cycle (0.64) was twice the in vivo value. Two-thirds of the Q fraction cells remained in the ventricular epithelium, resulting in a substantially low growth fraction of 0.73 compared with 1.0 in vivo. The embryonic murine cerebral explant, cultured in minimum essential medium, should be favorable for studies of cycle modulatory actions of cell external influences such as growth factors or neurotransmitters.