Cellular functions of Plks. Plk1-4 are implicated in cell cycle processes, such as centriole duplication (Plk2 and Plk4); DNA replication (Plk3); centrosome separation and maturation (Plk1); mitotic entry (Plk1); spindle formation, chromosome segregation and cytokinesis (Plk1). On the other hand, Plk2 and Plk5 (and probably Plk3) are involved in non-proliferative functions, such as neuron differentiation (Plk2 and Plk5) and synaptic homeostasis (Plk2). DDR, DNA damage response; SAC, spindle assembly checkpoint.