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Cell division

Fractal cycling

Nature Reviews Molecular Cell Biology volume 8, page 851 (2007)Cite this article

Mochida and Hunt now show that Apc3 and Cdc20/Fizzy (components of the APC/C) are dephosphorylated following CaMKII-dependent phosphorylation of Erp1, indicating that a Ca2+-responsive phosphatase also functions in meiotic exit. Moreover, phosphatase activity increased 40–50-fold in Ca2+-treated X. laevis extracts, and this activity correlated with the cytosolic Ca2+ transient. The phosphatase responsible is calcineurin (also known as PP2B), inhibition of which delayed the full activation of APC/C and hence delayed cyclin degradation in Ca2+-stimulated egg extracts.

Consistently, Ohsumi and colleagues showed that calcineurin is activated immediately after Ca2+ addition to arrested X. laevis egg extracts and that this occurred concomitantly with, but independently of, CaMKII activation. Inactivation of Cdk1 was delayed and could not be sustained when calcineurin was inhibited, and inhibition of both calcineurin and CaMKII prevented the formation of segregated nuclei and meiosis II exit. They suggest that calcineurin activity enhances CaMKII-mediated Erp1 degradation, facilitating full activation of the APC/C, although this remains to be determined. Nevertheless, both enzymes appear to be essential for, and synergistically inactivate, Cdk1 to exit meiosis II. They also showed that calcineurin activity negatively regulates later events that are required to form the diploid zygote, indicating that post-fertilization events are regulated, in part, by phosphatase oscillations.

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ORIGINAL RESEARCH PAPERS

  1. Mochida, S. & Hunt, T. Calcineurin is required to release Xenopus egg extracts from meiotic M phase. Nature 449, 336–340 (2007)

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  2. Nishiyama, T. et al. Transient activation of calcineurin is essential to initiate embryonic development in Xenopus laevis. Nature 449, 341–345 (2007)

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Authors
  1. Gemma K. Alderton
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Alderton, G. Fractal cycling. Nat Rev Mol Cell Biol 8, 851 (2007). https://doi.org/10.1038/nrm2284

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