Mitotic activity in the lens rudiment of the chicken embryo before and after the onset of crystallin synthesis : I. Results of treatment with Colcemid.

1. Previous work has shown that the lens rudiment of the chicken embryo starts producing crystallins in stage 14 at the beginning of invagination (Ikeda and Zwaan, 1966). To establish if this appearance of organ-specific proteins is coupled with changes in cell replication, the mitotic activity in the anlage was determined by Colcemid treatment in stages 10 to 17. No significant differences in activity were noted between the center and the periphery of the organ in the stages studied or between stages of development. 2. We conclude that cessation of cell replication and the onset of crystallin production are not directly linked. 3. A mitotic duration of 24 min and a total cell cycle time of 15 h were calculated. The latter value does not agree with data from earlier studies using autoradiography after3H-thymidine application. Possible reasons for the discrepancy are discussed and caution is urged in the interpretation of cell cycle data obtained by treatment with mitotic inhibitors.