Differential regulation of cyclin B1 degradation between the first and second meiotic divisions of bovine oocytes.
During mammalian oocyte maturation, two consecutive meiotic divisions are required to form a haploid gamete. For each meiotic division, oocytes must transfer from metaphase to anaphase, but maturation promoting factor (cyclin-dependent kinase 1/cyclin B1) activity would keep the oocytes at metaphase. Therefore, inactivation of maturation promoting factor is needed to finish the transition and complete both these divisions; this is provided through anaphase-promoting complex/cyclosome-dependent degradation of cyclin B1. The objective of this study was to examine meiotic divisions in bovine oocytes after expression of a full length cyclin B1 and a nondegradable N-terminal 87 amino acid deletion, coupled with the fluorochrome Venus, by microinjecting their complementary RNA (cRNA). Overexpression of full-length cyclin B1-Venus inhibited homologue disjunction and first polar body formation in maturing oocytes (control 70% vs. overexpression 16%; P < 0.05). However at the same levels of expression, it did not block second meiotic metaphase and cleavage of eggs after parthenogenetic activation (control: 82% pronuclei and 79% cleaved; overexpression: 91% pronuclei and 89% cleaved). The full length cyclin B1 and a nondegradable N-terminal 87 amino acid deletion caused metaphase arrest in both meiotic divisions, whereas degradation of securin was unaffected. Roscovitine, a potent cyclin-dependent kinase 1 (CDK1) inhibitor, overcame this metaphase arrest in maturing oocytes at 140 μM, but higher doses (200 μM) were needed to overcome arrest in eggs. In conclusion, because metaphase I (MI) blocked by nondegradable cyclin B1 was distinct from metaphase II (MII) in their different sensitivities to trigger CDK1 inactivation, we concluded that mechanisms of MI arrest differed from MII arrest.
College of Veterinary Medicine, Northwest A&F University, Shaanxi Stem Cell Engineering and Technology Center, Yangling, China.
W
W
Liu
J
J
Yin
G
G
Zhao
Y
Y
Yun
S
S
Wu
K T
KT
Jones
A
A
Lei
D000705:Anaphase; D064173:Anaphase-Promoting Complex-Cyclosome; D000818:Animals; D016203:CDC2 Protein Kinase / Q000037:antagonists & inhibitors / Q000378:metabolism; D002417:Cattle; D056744:Cyclin B1 / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004789:Enzyme Activation; D005260:Female; D015870:Gene Expression; D005786:Gene Expression Regulation; D018014:Gene Transfer Techniques / Q000662:veterinary; D008540:Meiosis / Q000235:genetics* / Q000502:physiology*; D008677:Metaphase / Q000187:drug effects / Q000502:physiology; D009154:Mutation / Q000235:genetics; D009865:Oocytes / Q000502:physiology* / Q000648:ultrastructure; D010312:Parthenogenesis; D011687:Purines / Q000494:pharmacology; D018075:RNA, Complementary / Q000235:genetics; D000077546:Roscovitine; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism / Q000502:physiology
D056744:Cyclin B1; D011687:Purines; D018075:RNA, Complementary; D000077546:Roscovitine; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome; D016203:CDC2 Protein Kinase