Illustrating the development of live kidney cells, specifically a metanephric kidney that has been cultured in vitro and imaged over 4 days. The fluorescence originates from a conditional YFP reporter, which is only activated in cells expressing Pax8. The fluorescent cells belong to the ureteric bud (the tree), the induced nephron progenitors cell (cells around the tree tips) and nephrons that are forming (the shapes forming within the tree). The YFP signal is viewed using a heat-map that has been overlaid onto the bright-field channel.