Centriole maturation requires daughter centriole assembly. (A) Schematic showing relative Cep120 levels on centrioles at stages of the cell cycle. The Cep120 fluorescence intensity at daughter (D, D1, and D2), mother (M), and grandmother (G) centrioles in U2OS cells was quantified at different cell cycle stages and presented as the indicated ratios. Mitotic U2OS cells with single centrioles at each pole were generated by depletion of Plk4. Results shown are a mean of two independent experiments (n = 50 for each cell cycle stage). (B) Maturation of the daughter centriole is dependent on the presence of a procentriole. (left) U2OS cells were transfected with control or Plk4 siRNA and stained for centrin (red), cenexin/Odf2 (green), and DNA (blue). (right) Mitotic cells with two centrioles (control siRNA) or single centrioles (Plk4 siRNA) at each spindle pole were scored for the presence or absence of cenexin/Odf2. Results shown are a mean of two independent experiments (n = 200). Insets are magnified images of the centrosome region. Data are means ± SD. Bar, 10 µm.