APC/CFZR-1 regulates centrosomal ZYG-1 to limit centrosome number

Aberrant centrosome numbers are associated with human cancers. The levels of centrosome regulators positively correlate with centrosome number. Thus, tight control of centrosome protein levels is critical. In Caenorhabditis elegans, the anaphasepromoting complex/cyclosome and its co-activator FZR-1 (APC/ CFZR-1),aubiquitinligase,negativelyregulatescentrosomeassembly through SAS-5 degradation. In this study, we report the C. elegans ZYG-1 (Plk4 in humans) as a potential substrate of APC/CFZR-1. Inhibiting APC/CFZR-1 or mutating a ZYG-1 destruction (D)-box leads to elevated ZYG-1 levels at centrosomes, restoring bipolar spindles andembryonicviabilitytozyg-1mutants,suggestingthatAPC/CFZR-1 influences centrosomal ZYG-1 viathe D-boxmotif. We also show the Slimb/βTrCP-binding (SB) motif is critical for ZYG-1 degradation, substantiatingaconservedmechanismbywhichZYG-1/Plk4stability is regulated by the SKP1–CUL1–F-box (Slimb/βTrCP)-protein complex (SCFSlimb/βTrCP)-dependent proteolysis via the conserved SBmotifinC.elegans.Furthermore,weshowthatco-mutatingZYG-1 SB and D-box motifs stabilizes ZYG-1 in an additive manner, suggesting that the APC/CFZR-1 and SCFSlimb/βTrCP ubiquitin ligases function cooperatively for timely ZYG-1 destruction in C. elegans embryos where ZYG-1 activity remains at threshold level to ensure normal centrosome number.