PCMD-1 stabilizes the PCM scaffold and facilitates centriole separation

Centrosomes are highly dynamic organelles, and maintaining their stability is crucial for spindle pole integrity and bipolar spindle formation. Centrosomes consist of a pair of centrioles surrounded by the pericentriolar material (PCM). In Caenorhabditis elegans, interactions between the PCM scaffold protein SPD-5 and the regulatory kinase PLK-1 are essential for PCM formation and disassembly. However, how PCM stability is established and maintained remains an open question. Here, we address this question by analyzing the function of PCMD-1, a protein that predominantly localizes to centrioles. Mutations in the predicted PLK-1 binding sites of PCMD-1 result in a reduction of centrosomal PLK-1 and PCMD-1 levels, leading to severe distortion of the PCM scaffold. The disorganization of the PCM is already evident during its formation and results in the assembly of a structurally unstable mitotic centrosome, which is unable to resist the microtubule pulling forces exerted on the spindle pole. As a consequence of a weakened PCM scaffold, the pulling forces are not effectively relayed to the entrapped centriole pair, resulting in delayed centriole separation in late anaphase. Together, these findings show that PCMD-1, which predominantly localizes to centrioles and tethers the PCM scaffold to them, is essential for stabilizing the entire PCM scaffold and ensuring timely centriole separation during PCM disassembly. We propose a model in which PCMD-1 initiates the ordered assembly of the PCM scaffold by biasing the PCM core to a certain intrinsic order around the centrioles. This intrinsic order acts as a seed that propagates throughout the surrounding micron-scale PCM scaffold, providing the necessary strength and structural integrity for the centrosome.