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PP2A Phosphatase Acts upon SAS-5 to Ensure Centriole Formation in C. elegans Embryos.
Developmental Cell,  April 19, 2011
kitagawa Laboratory, Centrosome Biology Laboratory
PP2A Phosphatase Acts upon SAS-5 to Ensure Centriole Formation in C. elegans Embryos.
Daiju Kitagawa, Isabelle Flückiger, Jolanta Polanowska, Debora Keller, Jérôme Reboul and Pierre Gönczy
Developmental Cell 20, 550-562, April 19, 2011 DOI:10.1016/j.devcel.2011.02.005

Centrosome duplication occurs once per cell cycle and ensures that the two resulting centrosomes assemble a bipolar mitotic spindle. Centriole formation is fundamental for centrosome duplication. In Caenorhabditis elegans, the evolutionarily conserved proteins SPD-2, ZYG-1, SAS-6, SAS-5 and SAS-4 are essential for centriole formation, but how they function is not fully understood. Here, we demonstrate that Protein Phosphatase 2A (PP2A) is also critical for centriole formation in C. elegans embryos. We find that PP2A subunits genetically and physically interact with the SAS-5/SAS-6 complex. Furthermore, we show that PP2A-mediated dephosphorylation promotes centriolar targeting of SAS-5 and ensures SAS-6 delivery to the site of centriole assembly. We find that PP2A is similarly needed for the presence of HsSAS-6 at centrioles and centriole formation in human cells. These findings lead us to propose that PP2A-mediated loading of SAS-6 proteins is critical at the onset of centriole formation.

Figure. PP2A phosphatase regulates centriolar targeting of SAS-5/SAS-6 complex
(A) To allow entry of DMSO or Calyculin A inside two cell-stage C. elegans embryos expressing GFP-SAS-5, the eggshell was pierced with a laser microbeam. Elapsed time after piercing is indicated in minutes. Embryos were then analyzed by spinning disk confocal microscopy to monitor centriolar GFP-SAS-5. Representative magnified images of centriolar GFP-SAS-5. Insets show a ~2x magnified view of centrosomes.
(B) Working model. SAS-5/SAS-6 interacts with the complex formed by the catalytic and structural subunits of the PP2A phosphatase (LET-92/PAA-1), with the association between SAS-6 and SUR-6 further promoting this interaction (step 1). Double lines indicate observed protein-protein interactions. Dephosphorylation of SAS-5 follows (step 2), after which the SAS-5/SAS-6 complex is recruited to the assembly site of centrioles (step 3).