Figure 4

Defined cells can be followed over multiple days. A) In order to set up the coordinate system, two black ink reference points are tattooed on the abdomen of mice; origin and reference. At T0, the distance L(ref) and the angle a(ref) are measured between the two reference points. For cell coordinates, the distance L(cell) and the angle a(cell) are measured between the cell and origin. B) At a subsequent timepoint (T1), small rotations in the position of the mouse alter a(ref) and a(cell), but not L(ref) and L(cell). a(ref) is measured again, and a(cell) is corrected by the difference in a(ref) at T0 and T1. Knowing L(cell) and a(cell), the positions of the previously recorded cells can be re-calculated. (Right panels) Merge of GFP (green) and background (cyan) overview images of the skin of a mouse at T = 0 and T = 24 hours, imaged with a low-magnification objective (5×). The same cells are found back using the coordinate system. Insets represent the boxed regions, which have been imaged with a higher magnification objective (20×).