Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

  • Letter
  • Published:

Phosphorylation of Erp1 by p90rsk is required for cytostatic factor arrest in Xenopus laevis eggs

This article has been updated


Until fertilization, the meiotic cell cycle of vertebrate eggs is arrested at metaphase of meiosis II by a cytoplasmic activity termed cytostatic factor (CSF)1, which causes inhibition of the anaphase-promoting complex/cyclosome (APC/C), a ubiquitin ligase that targets mitotic cyclins—regulatory proteins of meiosis and mitosis—for degradation2,3. Recent studies indicate that Erp1/Emi2, an inhibitor protein for the APC/C, has an essential role in establishing and maintaining CSF arrest4,5,6, but its relationship to Mos, a mitogen-activated protein kinase (MAPK) kinase kinase that also has an essential role in establishing CSF arrest7 through activation of p90 ribosomal S6 kinase (p90rsk)8,9, is unclear. Here we report that in Xenopus eggs Erp1 is a substrate of p90rsk, and that Mos-dependent phosphorylation of Erp1 by p90rsk at Thr 336, Ser 342 and Ser 344 is crucial for both stabilizing Erp1 and establishing CSF arrest in meiosis II oocytes. Semi-quantitative analysis with CSF-arrested egg extracts reveals that the Mos-dependent phosphorylation of Erp1 enhances, but does not generate, the activity of Erp1 that maintains metaphase arrest. Our results also suggest that Erp1 inhibits cyclin B degradation by binding the APC/C at its carboxy-terminal destruction box10, and this binding is also enhanced by the Mos-dependent phosphorylation. Thus, Mos and Erp1 collaboratively establish and maintain metaphase II arrest in Xenopus eggs. The link between Mos and Erp1 provides a molecular explanation for the integral mechanism of CSF arrest in unfertilized vertebrate eggs.

This is a preview of subscription content, access via your institution

Access options

Buy this article

Prices may be subject to local taxes which are calculated during checkout

Figure 1: Erp1 is present throughout the early embryonic cell cycle.
Figure 2: Erp1 is phosphorylated by p90rsk, depending on MosMAPK activity.
Figure 3: Phosphorylation of Erp1 at TSS increases its stability and is required for the establishment of metaphase arrest in meiosis II oocytes.
Figure 4: Phosphorylation of Erp1 at TSS enhances its CSF activity by increasing its binding affinity to the APC/C.

Similar content being viewed by others

Change history

  • 26 April 2007

    The addition of the word 'kinase' in the 9th line of the abstract


  1. Masui, Y. & Markert, C. L. Cytoplasmic control of nuclear behavior during meiotic maturation of frog oocytes. J. Exp. Zool. 177, 129–145 (1971)

    Article  CAS  Google Scholar 

  2. Harper, J. W., Burton, J. L. & Solomon, M. J. The anaphase-promoting complex: it's not just for mitosis any more. Genes Dev. 16, 2179–2206 (2002)

    Article  CAS  Google Scholar 

  3. Peters, J. M. The anaphase-promoting complex: proteolysis in mitosis and beyond. Mol. Cell 9, 931–943 (2002)

    Article  CAS  Google Scholar 

  4. Schmidt, A. et al. Xenopus polo-like kinase Plx1 regulates XErp1, a novel inhibitor of APC/C activity. Genes Dev. 19, 502–513 (2005)

    Article  CAS  Google Scholar 

  5. Tung, J. J. et al. A role for the anaphase-promoting complex inhibitor Emi2/XErp1, a homolog of early mitotic inhibitor 1, in cytostatic factor arrest of Xenopus eggs. Proc. Natl Acad. Sci. USA 102, 4318–4323 (2005)

    Article  ADS  CAS  Google Scholar 

  6. Shoji, S. et al. Mammalian Emi2 mediates cytostatic arrest and transduces the signal for meiotic exit via Cdc20. EMBO J. 25, 834–845 (2006)

    Article  CAS  Google Scholar 

  7. Sagata, N., Watanabe, N., Vande Woude, G. F. & Ikawa, Y. The c-mos proto-oncogene product is a cytostatic factor responsible for meiotic arrest in vertebrate eggs. Nature 342, 512–518 (1989)

    Article  ADS  CAS  Google Scholar 

  8. Bhatt, R. R. & Ferrell, J. E. The protein kinase p90 rsk as an essential mediator of cytostatic factor activity. Science 286, 1362–1365 (1999)

    Article  CAS  Google Scholar 

  9. Gross, S. D., Schwab, M. S., Lewellyn, A. L. & Maller, J. L. Induction of metaphase arrest in cleaving Xenopus embryos by the protein kinase p90Rsk. Science 286, 1365–1367 (1999)

    Article  CAS  Google Scholar 

  10. Miller, J. J. et al. Emi1 stably binds and inhibits the anaphase-promoting complex/cyclosome as a pseudosubstrate inhibitor. Genes Dev. 20, 2410–2420 (2006)

    Article  CAS  Google Scholar 

  11. Masui, Y. The elusive cytostatic factor in the animal egg. Nature Rev. Mol. Cell Biol. 1, 228–232 (2000)

    Article  CAS  Google Scholar 

  12. Kishimoto, T. Cell-cycle control during meiotic maturation. Curr. Opin. Cell Biol. 15, 654–663 (2003)

    Article  CAS  Google Scholar 

  13. Tunquist, B. J. & Maller, J. L. Under arrest: cytostatic factor (CSF)-mediated metaphase arrest in vertebrate eggs. Genes Dev. 17, 683–710 (2003)

    Article  CAS  Google Scholar 

  14. Liu, J. & Maller, J. L. Calcium elevation at fertilization coordinates phosphorylation of XErp1/Emi2 by Plx1 and CaMK II to release metaphase arrest by cytostatic factor. Curr. Biol. 15, 1458–1468 (2005)

    Article  CAS  Google Scholar 

  15. Rauh, N. R., Schmidt, A., Bormann, J., Nigg, E. A. & Mayer, T. U. Calcium triggers exit from meiosis II by targeting the APC/C inhibitor XErp1 for degradation. Nature 437, 1048–1052 (2005)

    Article  ADS  CAS  Google Scholar 

  16. Hansen, D. V., Tung, J. J. & Jackson, P. K. CaMKII and polo-like kinase 1 sequentially phosphorylate the cytostatic factor Emi2/XErp1 to trigger its destruction and meiotic exit. Proc. Natl Acad. Sci. USA 103, 608–613 (2006)

    Article  ADS  CAS  Google Scholar 

  17. Lorca, T. et al. Calmodulin-dependent protein kinase II mediates inactivation of MPF and CSF upon fertilization of Xenopus eggs. Nature 366, 270–273 (1993)

    Article  ADS  CAS  Google Scholar 

  18. Schmidt, A., Rauh, N. R., Nigg, E. A. & Mayer, T. U. Cytostatic factor: an activity that puts the cell cycle on hold. J. Cell Sci. 119, 1213–1218 (2006)

    Article  CAS  Google Scholar 

  19. Haccard, O. et al. Induction of metaphase arrest in cleaving Xenopus embryos by MAP kinase. Science 262, 1262–1265 (1993)

    Article  ADS  CAS  Google Scholar 

  20. Yamamoto, T. M., Iwabuchi, M., Ohsumi, K. & Kishimoto, T. APC/C–Cdc20-mediated degradation of cyclin B participates in CSF arrest in unfertilized Xenopus eggs. Dev. Biol. 279, 345–355 (2005)

    Article  CAS  Google Scholar 

  21. Murray, A. W. & Kirschner, M. W. Cyclin synthesis drives the early embryonic cell cycle. Nature 339, 275–280 (1989)

    Article  ADS  CAS  Google Scholar 

  22. Lohka, M. J. & Maller, J. L. Induction of nuclear envelope breakdown, chromosome condensation, and spindle formation in cell-free extracts. J. Cell Biol. 101, 518–523 (1985)

    Article  CAS  Google Scholar 

  23. Murray, A. W., Solomon, M. J. & Kirschner, M. W. The role of cyclin synthesis and degradation in the control of maturation promoting factor activity. Nature 339, 280–286 (1989)

    Article  ADS  CAS  Google Scholar 

  24. Ohsumi, K., Koyanagi, A., Yamamoto, T. M., Gotoh, T. & Kishimoto, T. Emi1-mediated M-phase arrest in Xenopus eggs is distinct from cytostatic factor arrest. Proc. Natl Acad. Sci. USA 101, 12531–12536 (2004)

    Article  ADS  CAS  Google Scholar 

  25. Gotoh, Y. et al. Characterization of recombinant Xenopus MAP kinase kinases mutated at potential phosphorylation sites. Oncogene 9, 1891–1898 (1994)

    CAS  PubMed  Google Scholar 

  26. Dupre, A., Jessus, C., Ozon, R. & Haccard, O. Mos is not required for the initiation of meiotic maturation in Xenopus oocytes. EMBO J. 21, 4026–4036 (2002)

    Article  CAS  Google Scholar 

  27. Dumont, J., Umbhauer, M., Rassinier, P., Hanauer, A. & Verlhac, M. H. p90Rsk is not involved in cytostatic factor arrest in mouse oocytes. J. Cell Biol. 169, 227–231 (2005)

    Article  CAS  Google Scholar 

  28. Lefebvre, C. et al. Meiotic spindle stability depends on MAPK-interacting and spindle-stabilizing protein (MISS), a new MAPK substrate. J. Cell Biol. 157, 603–613 (2002)

    Article  CAS  Google Scholar 

  29. Iwabuchi, M., Ohsumi, K., Yamamoto, T. M., Sawada, W. & Kishimoto, T. Residual Cdc2 activity remaining at meiosis I exit is essential for meiotic M–M transition in Xenopus oocyte extracts. EMBO J. 19, 4513–4523 (2000)

    Article  CAS  Google Scholar 

Download references


We thank J. L. Maller and M. Iwabuchi for antibodies, M. Mori for CA- and KD-p90rsk2 proteins, K. Tachibana and E.Okumura for discussions, and M. J. Lohka and L. A. Jaffe for reading the manuscript. This work was also supported by grants from the Ministry of Education, Culture, Sports, Science and Technology of Japan to K.O. and T.K.

Author information

Authors and Affiliations


Corresponding author

Correspondence to Keita Ohsumi.

Ethics declarations

Competing interests

Reprints and permissions information is available at The authors declare no competing financial interests.

Supplementary information

Supplementary information

This file contains Supplementary Figures S1 – S7 with Legends, Supplementary Methods and additional references. (PDF 1668 kb)

Rights and permissions

Reprints and permissions

About this article

Cite this article

Nishiyama, T., Ohsumi, K. & Kishimoto, T. Phosphorylation of Erp1 by p90rsk is required for cytostatic factor arrest in Xenopus laevis eggs. Nature 446, 1096–1099 (2007).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing