Time-lapse imaging of mGFP labeled UB cells in a Rosa26mTmG kidney culture (related to Figure 6). E12.5 kidneys carrying a Rosa26mTmG reporter and RetCreERT2 were treated with 4-OH tamoxifen for one hour and cultured overnight before being imaged every 14 minutes on a confocal microscope. All cells initially expressed mTomato, and Cre-mediated recombination in a small fraction of UB tip cells caused them to switch to express mGFP. The 3D-rendered images from z-stacks of the mGFP+ UB cells, at each time point, were assembled to make the movie. The movie shows that normal UB tip cells are highly dynamic in shape, extending and retracting long, thin processes in different directions and making transient contacts with other, non-adjacent UB tip cells.