Assay data from the primary screen. (a) The graph represents the mean percentages of p27 positive cells detected across all wells in each of the 44 screening plates (blue circles). The data are further stratified by treatment: Red squares indicate the mean percentages obtained with the negative control (dimethyl sulfoxide; DMSO), yellow triangles indicate the mean percentages obtained with the positive control (roscovitine). Blue diamonds indicate the mean percentages obtained by staining without the primary p27 antibody (non-specific background staining). (b) Sum Z-scores. The heat map represents the sum of Z-scores from each well in 22 plates. DMSO (negative control) was added to column 1, roscovitine (positive control) to column 2, and in some cases to columns 22 and 23, and the non-specific staining was performed in columns 23 and 24. (c) Heat map of a representative screening plate showing potential hits based on their Z score. The first column on the plate contained the negative control DMSO, the second column contained the positive control agent roscovitine, and columns 23 and 24 were stained without the primary p27 antibody (non-specific background staining). The well marked with a black square was identified as containing a false positive compound, whereas the red circle indicates a potential hit. A representative micrograph from well L12 (potential hit) is shown to the right.