Okadaic acid induces premature chromosome condensation reflecting the cell cycle progression in one-cell stage mouse embryos.
Haploid parthenogenetic embryos as well as fertilized mouse eggs were treated in vitro with 1-10 microM okadaic acid (OA) at the one-cell stage. Cytogenetic analysis detected that OA induces nuclear envelope breakdown (NEBD) and premature condensation of interphase chromosomes in pronuclei as well as in 2nd polar body (PB) nuclei. G1-, S-, and G2-type prematurely condensed chromosomes (PCC) were found in pronuclei of embryos of different age, which reflects their progression through the first cell cycle. In nuclei from 2nd PBs only G1- and S-type PCC were observed. Using the types of PCC as a criterion of different phases of the cell cycle, it was possible to estimate that in haploid parthenogenetic embryos G1-phase lasts until 5.5 hr post activation (hpa), S-phase takes from 4.5 to 9.5 hpa, and from 8.5 hpa G2-phase had started. Second PBs were found to be in G1-phase until 6.5 hpa and S-phase started in some as early as 5.5 hpa, but in most not before 7.5 hpa. Treatment with OA visualizes G1-chromosomes in pronuclei as well as in 2nd PBs, and it is easy to count the number of these chromosomes and recognize a T6 marker chromosome. The possibility to apply cytogenetic analysis of G1-chromosomes from 2nd PBs for a more accurate detection of maternal meiotic nondisjunction is discussed.
Reproductive Genetics Institute, Illinois Masonic Medical Center, Chicago 60657.
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Dyban
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De Sutter
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Verlinsky
D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002875:Chromosomes / Q000187:drug effects* / Q000648:ultrastructure; D004988:Ethers, Cyclic / Q000494:pharmacology*; D005260:Female; D006238:Haploidy; D066298:In Vitro Techniques; D051379:Mice; D019319:Okadaic Acid; D010063:Ovum / Q000187:drug effects / Q000648:ultrastructure; D010312:Parthenogenesis; D010749:Phosphoprotein Phosphatases / Q000037:antagonists & inhibitors; D015053:Zygote / Q000187:drug effects* / Q000648:ultrastructure
D004988:Ethers, Cyclic; D019319:Okadaic Acid; D010749:Phosphoprotein Phosphatases