Matrimony ties Polo down: can this kinase get free?

Cell cycle progression in female meiotic systems is characterized by the presence of two or more pre-programmed arrests. One such arrest is invariable throughout all species--a lengthy G(2) arrest that separates the end of pachytene (by which homologous chromosomes have condensed, paired and undergone recombination) from nuclear envelope breakdown (NEB). The termination of G(2) arrest (as defined by NEB) and the subsequent entry of the oocyte into prometaphase is regulated by an intracellular signaling cascade whose ultimate feature is the activation of the cyclin B-Cdk1 complex by the Cdc25 phosphatase family. In oocytes, activation of Cdc25 is often mediated by Polo-like kinases (Plks). Recent work by Xiang et al. demonstrated that in Drosophila female meiosis, Polo's role in promoting NEB is regulated by meiosis-specific stoichiometric inhibitor called Matrimony (Mtrm), which binds to the C-terminal Polo-box domain (PBD) of Polo. In addition to a PBD-binding site, Mtrm contains putative Plk and cyclin B-Cdk1 phosphorylation consensus motifs. These motifs suggest a unique mechanism of Polo inhibition by Mtrm and a possible auto-amplification loop by which cyclin B-Cdk1-mediated destruction or dissociation of Mtrm from Polo allows for rapid and irreversible G(2) exit and entry into prometaphase.

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