Multimodal mechanisms of human centriole engagement and disengagement
The DNA and the centrioles are the only cellular structures that uniquely replicate to produce identical copies, which is crucial for proper chromosome segregation in mitosis. A new centriole termed "daughter" is progressively assembled adjacent to a pre-existing, "mother" centriole. Only after the daughter centriole is structurally completed as an identical copy, it disengages from its mother to become the core of a new functional centrosome. The mechanisms preventing precocious disengagement of the immature copy have been previously unknown. Here, we identify three key centriole-associated mechanisms that maintain the mother-daughter engagement: the cartwheel, the torus, and the pericentriolar material pathways. Among these, the torus is critical for establishing the characteristic orthogonal engagement between the mother and daughter centrioles. Furthermore, we show that the engagement mediated by the cartwheel and the torus pathways is released stepwise through structural changes in the daughter centriole, known as centriole blooming and centriole distancing, respectively. Disruption at any stage of these structural transitions leads to the failure of all subsequent steps, ultimately blocking centriole disengagement and centrosome conversion at the end of mitosis. Overall, this study provides a comprehensive understanding of how the maturing daughter centriole progressively disengages from its mother through multiple maturation steps, to ensure its complete structure and conversion into an independent centrosome.