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Published 11 September 2006. doi:10.1083/jcb.200604140
The Rockefeller University Press, 0021-9525 $8.00
JCB, Volume 174, Number 6, 791-801
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Article

 Mouse Emi2 is required to enter meiosis II by reestablishing cyclin B1 during interkinesis

Suzanne Madgwick1, David V. Hansen2,3, Mark Levasseur1, Peter K. Jackson2,3, and Keith T. Jones1

1 Institute for Cell and Molecular Biosciences, The Medical School, University of Newcastle, Newcastle NE2 4HH, England, UK
2 Department of Pathology and 3 Program in Cancer Biology, Stanford University School of Medicine, Stanford, CA 94305

Correspondence to Keith T. Jones: k.t.jones{at}ncl.ac.uk; or Suzanne Madgwick: suzanne.madgwick{at}ncl.ac.uk

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.

D.V. Hansen and P.K. Jackson's current address is the Department of Tumor Biology and Angiogenesis, Genentech, Inc., South San Francisco, CA 94080.

Abbreviations used in this paper: APC, anaphase-promoting complex/cyclosome; Bub, budding uninhibited by benzimidazole; CSF, cytostatic factor; Emi, early mitotic inhibitor protein; GV, germinal vesicle; GVBD, GV breakdown; Mad, mitotic arrest deficient; MISS, MAPK-interacting and spindle-stabilizing protein; MO, morpholino; MPF, M-phase (maturation)–promoting factor; PB, polar body.


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