Mitosis is orchestrated by several protein kinases including Cdks, Plks and 
Aurora kinases. Despite considerable progress toward understanding the 
individual function of these protein kinases, how their activity is coordinated 
in space and time during mitosis is less well understood. In a recent article 
published in the Journal of Cell Biology, we show that CDK-1 regulates PLK-1 
activity during mitosis in C. elegans embryos through multisite phosphorylation 
of the PLK-1 activator SPAT-1 (Aurora Borealis, Bora in human). SPAT-1 variants 
mutated on CDK-1 phosphorylation sites results in severe delays in mitotic 
entry, mimicking embryos lacking spat-1 or plk-1 function. We further show that 
SPAT-1 phosphorylation by CDK-1 promotes its binding to PLK-1 and stimulates 
PLK-1 phosphorylation on its activator T-loop by Aurora A kinase in vitro. 
Likewise, we find that phosphorylation of Bora by Cdk1 promotes phosphorylation 
of human Plk1 by Aurora A suggesting that this mechanism is conserved in humans. 
These results indicate that Cdk1 regulates Plk1 by boosting its kinase activity. 
Here we discuss these recent findings and open questions regarding the 
regulation of Plk1/PLK-1 by Cdk1/CDK-1 and Bora/SPAT-1.