Quantitative imaging of B1 cyclin expression across the cell cycle using green fluorescent protein tagging and epi-fluorescence

In this work we report the number of cyclin B1 proteins tagged with enhanced green fluorescent protein (eGFP) in fixed U-2 OS cells across the cell cycle. We use a quantitative analysis of epi-fluorescence to determine the number of eGFP molecules in a non-destructive way, and integrated over the cell we find 104 to 105 molecules. Based on the measured number of eGFP tagged cyclin B1 proteins, knowledge of cyclin B1 dynamics through the cell cycle, and the cell morphology, we identify the stages of cells in the cell cycle