Analysis of the variability and of the lengthening of intercleavage times during the cleavage stages of Nothobranchius guentheri.

Abstract

By means of time-lapse cinematography the early development of the annual fish Nothobranchius guentheri was recorded on 16-mm film up to the tenth cleavage round. Analysis of the films showed that the mean intercleavage time is much the same up to the seventh cleavage. Thereafter, intercleavage times increase, with steps of about 30 min or a multiple of it, at each subsequent cleavage. As development proceeds, the variability in intercleavage times increases. A positive correlation of sister intercleavage times exists from the seventh generation, whereas intercleavage times of mother-daughter cells are positively correlated in the ninth generation. The results suggest that the lengthening of the cell cycle after the seventh cleavage is due to the insertion of a time period in a programmable mitotic clock. The duration of this time period differs between the different cell lines of a pedigree, probably because of a difference in cell volume. Variability in intercleavage times might also arise as a result of some random transition which the cells traverse only once per 5 min with a transition probability of 0.67/5 min.