Polo-like kinase 1 (Plk1) is an important mitotic kinase that is crucial for 
entry into mitosis after recovery from DNA damage-induced cell cycle arrest. 
Plk1 activation is promoted by the conserved protein Bora (SPAT-1 in C. 
elegans), which stimulates the phosphorylation of a conserved residue in the 
activation loop by the Aurora A kinase. In a recent article published in Cell 
Reports, we show that the master mitotic kinase Cdk1 contributes to Plk1 
activation through SPAT-1/Bora phosphorylation. We identified 3 conserved Sp/Tp 
residues that are located in the N-terminal, most conserved part, of 
SPAT-1/Bora. Phosphorylation of these sites by Cdk1 is essential for Plk1 
function in mitotic entry in C. elegans embryos and during DNA damage checkpoint 
recovery in mammalian cells. Here, using an untargeted Förster Resonance Energy 
Transfer (FRET) biosensor to monitor Plk1 activation, we provide additional 
experimental evidence supporting the importance of these phosphorylation sites 
for Plk1 activation and subsequent mitotic entry after DNA damage. We also 
briefly discuss the mechanism of Plk1 activation and the potential role of Bora 
phosphorylation by Cdk1 in this process. As Plk1 is overexpressed in cancer 
cells and this correlates with poor prognosis, understanding how Bora 
contributes to Plk1 activation is paramount for the development of innovative 
therapeutical approaches.