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Securin regulates entry into M-phase by modulating the stability of cyclin B


Timely progression into mitosis is necessary for normal cell division. This transition is sensitive to the levels of cyclin B, the regulatory subunit of the master mitotic kinase, Cdk1. Cyclin B accumulates during G2 and prophase when its rate of destruction by the anaphase promoting complex (APC) is low1. Securin is also an APC substrate and is known for its role in inactivating the cohesin-cleaving enzyme, separase, until the metaphase to anaphase transition. Here we show that securin has an additional role in cell-cycle regulation, that of modulating the timing of entry into M-phase. In mouse oocytes, excess securin caused stabilization of cyclin B and precocious entry into M-phase. Depletion of securin increased cyclin B degradation, resulting in delayed progression into M-phase. This effect required APC activity and was reversed by expression of wild-type securin. These data reveal a role for securin at the G2M transition and suggest a more general mechanism whereby physiological levels of co-competing APC substrates function in modulating the timing of cell-cycle transitions.

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Figure 1: Overexpression of securin causes the release of mouse GV-stage oocytes from prophase arrest.
Figure 2: Securin expression and MO-induced depletion in prophase-arrested GV-stage oocytes.
Figure 3: Depletion of securin inhibits entry into M-phase.
Figure 4: Securin depletion leads to delayed spontaneous activation of MII-arrested oocytes.


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This work was supported by an MRC grant to J. C. We thank Marc Kirschner, Mary Herbert, Alex McDougall, Michael Klymkowsky, Yu-Li Wang, Zoi Lygerou and Jonathan Pines for providing us with constructs and Tasos Siskoglou and Shamshad Cockcroft for their help with instruments and technology.

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Correspondence to Petros Marangos or John Carroll.

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Marangos, P., Carroll, J. Securin regulates entry into M-phase by modulating the stability of cyclin B. Nat Cell Biol 10, 445–451 (2008).

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