Centriole duplication and segregation cycle. A Plk1-dependent modification during G2/M is required to produce MTOC-competent centrioles during late mitosis and early G1 (modified centrioles [blue] and surrounded by PCM [yellow]). Only modified centrioles can duplicate in the following S phase, in which the capacity of the duplication is limited by centriole engagement to form one daughter centriole per mother centriole. Newly formed daughter centrioles can neither duplicate nor recruit PCM (orange and marked by prohibited signs), which prevents the assembly of their own daughter. These unmodified centrioles segregate equally during cell division by tethering to MTOC-competent centrioles that are capable of associating with spindle poles.