Identification of human phosphatases required for normal mitosis. (A) A model for the T loop–mediated kinase activation. Below is a schematic of the human protein phosphatase superfamily covering the phosphoprotein phosphatases (PPP), the metallophosphatases (PPM), and the phosphotyrosine protein (PTP) and dual-specificity phosphatases (DUSPs) modified from Chen et al. (2007). The number of phosphatase subunits screened in each subfamily is indicated. (B) The screening procedure and the phenotypes expected are categorized using Roman numerals together with a brief description of the underlying causes. (C) HeLa cells were transfected with siRNA pools for 78 human phosphatase subunits, fixed after 48 h, and stained with DAPI to reveal the DNA and nuclear morphology. Abnormal nuclear morphology was scored according to the categories (I–V) described and is expressed as a histogram sorted from high to low (n = 3). The dotted line indicates twice the median value for nuclear abnormalities. For verification, HeLa cells were transfected with the four siRNA duplexes (06–09) making up the PPP6C siRNA pool, fixed after 48 h, and then stained with DAPI to reveal the DNA and nuclear morphology. Numbers in the top left corner correspond to the siRNA library pool used. Con., control. Bar, 10 µm.