Caption: 
Time-lapse movie of blood progenitor cells dividing and differentiating in culture. The brightness of green fluorescence indicates the amount of the regulatory protein PU.1 present in each cell. Green fluorescence images are acquired at a lower frame rate compared to the gray bright-field images of the cells. Time is given in hours.
Video Credit: 
Hao Yuan Kueh, Michael Elowitz and Ellen Rothenberg/Caltech