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 time homologous chromosomes have condensed, paired and undergone recombination(1)) 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).(2-6) Recent work by Xiang et al. demonstrated that in Drosophila female meiosis, Polo's role in promoting NEB is regulated by a meiosis-specific stoichiometric inhibitor called Matrimony ( Mtrm), which binds to the C-terminal Polo-box domain ( PBD) of Polo.(7) 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.