Cell Cycle

Mastering Early Divisions

Science Signaling  30 Oct 2012:
Vol. 5, Issue 248, pp. ec283
DOI: 10.1126/scisignal.2003731

The regulation of canonical mitotic cell cycles is well understood, but the basic principles of the rapid, synchronized early mitotic divisions in embryos remain a mystery. Early embryos lack key mitotic regulators, such as checkpoints, the anaphase-promoting complex/cyclosome (APC/C)–inhibitory protein Emi1, and the inhibitory phosphorylations of cyclin-dependent kinase 1 (Cdk1). Working in Xenopus embryos, Tischer et al. identified XErp1 (also known as Emi2) as a mitotic APC/C-inhibitor essential for early mitotic divisions. The mitotic APC/C-inhibitory activity of XErp1 is positively regulated by protein kinase A (PKA) and protein phosphatase IIA (PP2A), which antagonizes Cdk1’s inhibitory effect on XErp1. Thus, Cdk1 and PP2A/PKA appear to act antagonistically to control XErp1 activity, which results in the oscillatory activation and inactivation of the APC/C required for fast and synchronous mitotic divisions.

T. Tischer, E. Hörmanseder, T. U. Mayer, The APC/C inhibitor XErp1/Emi2 is essential for Xenopus early embryonic divisions. Science 338, 520–524 (2012). [Abstract] [Full Text]