Checkpoint control of the G2/M phase transition during the first mitotic cycle in mammalian eggs.
The high incidence of chromosomally abnormal human embryos is frequently assumed to be due to a lack of checkpoint controls operating during early embryogenesis. In our study we have analysed when these mechanisms first become functional. Mouse oocytes treated in late metaphase I with either of two different cyclin-dependent kinase inhibitors [butyrolactone 1 (BL1) or 6-dimethylaminopurine (6-DMAP)] form nuclei in the cytoplasm. BL1-treated eggs enter S-phase at 16-18 h post-treatment and, after completion of DNA synthesis, cleave to 2-cell stage embryos. 6-DMAP treatment results in the rapid initiation of DNA synthesis, its completion by 12 h and then arrest in the G2 phase. Thus, two different cell cycle stages can be obtained at the same time point after the initiation of treatment: G1- after BL1 and G2-staged nuclei after 6-DMAP treatment. That this approach greatly facilitates cell cycle studies has been shown by analysing checkpoint function during the first division. Whilst G2-staged eggs enter M phase within 2-3 h when 6-DMAP is washed out, the onset of M phase is delayed after their fusion to G1 (BL1) cells. Here M phase occurs only after the less advanced nucleus completes DNA replication. Our results indicate that checkpoints in mammalian eggs are functional during the first mitotic cycle.
Fulka
J
J
The Institute of Animal Production, CS-104 01 Prague 10, Czech Republic.
First
N L
NL
Fulka1
J
J
Moor
R M
RM
D015107:4-Butyrolactone / Q000031:analogs & derivatives / Q000494:pharmacology; D000225:Adenine / Q000031:analogs & derivatives / Q000494:pharmacology; D000818:Animals; D018844:Cyclin-Dependent Kinases / Q000037:antagonists & inhibitors; D004247:DNA / Q000096:biosynthesis; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D016193:G1 Phase; D016195:G2 Phase; D051379:Mice; D008810:Mice, Inbred C57BL; D008808:Mice, Inbred CBA; D008938:Mitosis; D009865:Oocytes / Q000166:cytology* / Q000378:metabolism; D015053:Zygote
D004791:Enzyme Inhibitors; C001020:N(6),N(6)-dimethyladenine; C082868:butyrolactone I; D004247:DNA; D018844:Cyclin-Dependent Kinases; D000225:Adenine; D015107:4-Butyrolactone