Centriole cycle, PLK4 licensing, and bipolar spindle formation
Centrosome duplication is licensed once per cell cycle by the master kinase PLK4, which recruits SAS-6 to initiate procentriole formation perpendicular to each parental centriole. PLK4 is unusual in that it auto-phosphorylates itself to promote its own proteasomal degradation — a negative feedback that prevents over-duplication. After S phase, centrosomes mature via PCM expansion (γ-TuRC recruitment), separate in G2/M, and nucleate the bipolar spindle essential for faithful chromosome segregation.