Centriolar satellite distribution reflects cotranslational transport of certain centrosomal/ciliary clients. (A) Immunofluorescence micrographs and quantification of cytoplasmic PCNT signal in control and PCM1 siRNA-treated cells. Depletion of PCM1 leads to a significant decrease in the number of PCNT foci. Error bars are the mean ± SD. N = 211 control cells and 171 PCM1 siRNA cells. Data were analyzed using the Mann–Whitney test; ****P < 0.0001. (B and C) smFISH combined with immunofluorescence microscopy in control cells and cells depleted of PCM1. PCM1 depletion impairs PCNT mRNA localization around the centrosome in prometaphase (B), reflecting a loss of cotranslational targeting. However, the total number of PCNT mRNA foci assessed in interphase remains almost unchanged (C). Error bars in (C) are the mean ± SD. N = 33 prometaphase-stage and 189 interphase cells (control), 30 and 196 cells (PCM1 siRNA). A Mann–Whitney test was used to assess statistical significance; ****P < 0.0001, *P < 0.05. (D) Immunofluorescence micrographs of PCM1 in control and PCNT KO cells. Loss of PCNT does not impact PCM1 localization in interphase but compromises its concentration near centrosomes in pro- and prometaphase. N = 154 prometaphase and 348 interphase cells (control), 161 and 355 cells (PCNT KO). Localization groups were compared using the Mann–Whitney test, *P < 0.05. (E) Revised model of centriolar satellite function: centriolar satellites are sites of translation of centrosomal and ciliary proteins. Their concentration close to centrosomes in vertebrates is a byproduct of cotranslational targeting of certain centrosomal/ciliary clients including PCNT. Scale bars, 10 µm (A), 5 µm (B–D), 1 µm (insets).