Mouse Emi2 is required to enter meiosis II by reestablishing cyclin B1 during interkinesis.
During interkinesis, a metaphase II (MetII) spindle is built immediately after the completion of meiosis I. Oocytes then remain MetII arrested until fertilization. In mouse, we find that early mitotic inhibitor 2 (Emi2), which is an anaphase-promoting complex inhibitor, is involved in both the establishment and the maintenance of MetII arrest. In MetII oocytes, Emi2 needs to be degraded for oocytes to exit meiosis, and such degradation, as visualized by fluorescent protein tagging, occurred tens of minutes ahead of cyclin B1. Emi2 antisense morpholino knockdown during oocyte maturation did not affect polar body (PB) extrusion. However, in interkinesis the central spindle microtubules from meiosis I persisted for a short time, and a MetII spindle failed to assemble. The chromatin in the oocyte quickly decondensed and a nucleus formed. All of these effects were caused by the essential role of Emi2 in stabilizing cyclin B1 after the first PB extrusion because in Emi2 knockdown oocytes a MetII spindle was recovered by Emi2 rescue or by expression of nondegradable cyclin B1 after meiosis I.
Madgwick
Suzanne
S
Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle NE2 4HH, England, UK. suzanne.madgwick@ncl.ac.uk
Hansen
David V
DV
Levasseur
Mark
M
Jackson
Peter K
PK
Jones
Keith T
KT
D000818:Animals; D018797:Cell Cycle Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D002454:Cell Differentiation / Q000502:physiology; D002467:Cell Nucleus / Q000378:metabolism / Q000648:ultrastructure; D019926:Cyclin B / Q000378:metabolism*; D056744:Cyclin B1; D048749:Cytokinesis / Q000502:physiology*; D015536:Down-Regulation / Q000502:physiology; D044783:F-Box Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D005260:Female; D008540:Meiosis / Q000502:physiology*; D008677:Metaphase / Q000502:physiology; D051379:Mice; D008870:Microtubules / Q000378:metabolism / Q000648:ultrastructure; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D009865:Oocytes / Q000378:metabolism* / Q000648:ultrastructure; D009866:Oogenesis / Q000502:physiology*; D008941:Spindle Apparatus / Q000378:metabolism / Q000648:ultrastructure
C534700:Ccnb1 protein, mouse; D018797:Cell Cycle Proteins; D019926:Cyclin B; D056744:Cyclin B1; C509434:Emi2 protein, mouse; D044783:F-Box Proteins; D016376:Oligonucleotides, Antisense