Microtubule dependence of chromosome cycles in Xenopus laevis blastomeres under the influence of a DNA synthesis inhibitor, aphidicolin.
The spindle-assembly checkpoint of the cell cycle develops in Xenopus laevis embryos at the midblastula transition (MBT). Our previous experiments using animal-cap blastomeres indicate that the checkpoint is regulated by a mechanism that depends on age, but not on the nucleocytoplasmic (N/C) ratio (Clute and Masui, 1995). In the present study, the time of appearance of the spindle-assembly checkpoint is examined in animal-cap blastomeres whose N/C ratio is reduced by treatment with aphidicolin. Animal-cap blastomeres treated with aphidicolin from the 2-cell stage cleave more slowly after 4th cleavage, in a dose-dependent manner, but cleavage and chromosome cycles continue up to the 11th to 13th cleavage and then arrest. Blastomeres treated with aphidicolin have a reduced DNA content and N/C ratio compared to control blastomeres of the same age. Nevertheless, nocodazole-sensitive chromosome cycles appear at the same time as in control blastomeres, at 3 to 5 hr after 5th cleavage, regardless of the N/C ratio. The arrest in interphase caused by treating blastula stage animals caps with aphidicolin can be reversed by treatment with caffeine. The caffeine-induced mitosis becomes sensitive to nocodazole after the MBT, but not before. Therefore, the same mechanism which stabilizes maturation-promoting factor activity in the absence of a mitotic spindle also operates after the MBT in blastomeres that are treated with aphidicolin, if mitosis is induced by caffeine. This mechanism may involve the translation of a maternal mRNA at the time of the MBT, as suggested previously.
Clute
P
P
Department of Zoology, University of Toronto, Ontario, Canada. pc228@cam.ac.uk
Masui
Y
Y
D000818:Animals; D016590:Aphidicolin / Q000494:pharmacology*; D001757:Blastomeres / Q000187:drug effects*; D002453:Cell Cycle / Q000502:physiology*; D002875:Chromosomes; D004247:DNA / Q000096:biosynthesis / Q000187:drug effects; D008870:Microtubules / Q000502:physiology*; D015739:Nocodazole / Q000494:pharmacology; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology*; D014982:Xenopus laevis / Q000196:embryology
D019384:Nucleic Acid Synthesis Inhibitors; D016590:Aphidicolin; D004247:DNA; D015739:Nocodazole