Supplementary Movie 1

Time-lapse imaging of Hoxb7^Cre/+;mTmG;Hnf1b^fl/+ kidney shows first branching events. Tip domain with active cell movements and trunk with lumen formation can both be seen. By the end of the movie, nascent nephrons (Red cells) are observed. One image is taken every 10 minutes. Green is mG expression in Cre expressing cells. Red is mT expression in Cre non-expressing cells. Mitotic cells can be easily detected as they become round before division.