Fig. S4

Controls for the timing of recombination using the duration of 4-OHT-exposure; analysis of background-recombination in the Beta-bow system at 30 dpf. (A) Maximum intensity projection of the islets from 30 dpf Tg(ins:beta-bow); Tg(ins:CreER^T2) animals. Embryos were incubated with 1 uM 4-OHT from 6 to 12 hpf. The 4-OHT was washed away at 12 hpf, two hours before the onset of insulin expression in the dorsal-bud-derived beta-cells. 6 out of 7 islets (left) showed no recombination, while 1 out of 7 islets (right) displayed six cells (arrowhead) exhibiting background recombination. All cells with background recombination were dichromatic. No trichromatic cells were observed. (B) Maximum intensity projection of 30 dpf islets from Tg(ins:beta-bow); Tg(ins:CreER^T2) animals showing low leaky recombination in the absence of 4-OHT-incubation, as assessed by the expression of CFP or YFP. 8 out of 10 islets (left) showed no recombination, while 2 out of 10 islets (right) displayed two cells each (arrowhead) exhibiting background recombination. All cells exhibiting background recombination were dichromatic. No trichromatic cells were observed. Dichromatic cells can form as a result of a single-recombination event in Tg(ins:beta-bow). The probability of a single-recombination event was estimated to be ≈ 0.0005 (see materials and methods). Trichromatic cells require at least two recombination events to form. The probability of two recombination events without 4-OHT-induction was estimated to be 2.5E^-7 (see materials and methods). Scale bars, 50 μm.