CELL PROLIFERATION IN EMBRYONIC MOUSE NEURAL TUBE FOLLOWING URETHANE EXPOSURE

A comparative autoradiographic study of the cell cycle in normal 10-day mouse embryos and in embryos exposed to urethane showed an increase of 4.5 hours in the cycle time of the experimental group. Initially urethane interfered with the migration of some unlabeled premitotic nuclei to the germinal zone, resulting in extraventricular mitoses. A transient increase in the mitotic index and proportion of metaphases suggested a lengthened mitotic time but this was of brief duration and would not contribute significantly to the overall increased cycle time. The G2 period of cells which incorporated thymidine-3H in the presence of urethane was significantly lengthened as were the S and G1 periods and some injured cells died in interphase or mitosis. The new lengthened generation time of embryo neural tubes exposed to urethane resembles that of older, 11-day embryos. This suggests the possibility that cells with a short cycle may be preferentially killed by urethane, leaving the determination of mean cycle time to more differentiated cells. © 1969.