Fig. 4.

Fluorescent reporters differ in their susceptibility to basal CreER^T2 activity. a Representative confocal images of whole mount retinas from animals carrying Cdh5(PAC)-CreER^T2 and either Ai14, Ai3, mTmG, or the R26R-EYFP reporter. Endothelial cells are labeled with IB4 (isolectin B4), in red, and fluorescent proteins expressed by the individual reporters are depicted in green. Left column panels: Both the Ai14 and the Ai3 reporters appear to have a low recombination threshold, as basal (non-Tamoxifen induced) Cdh5(PAC)-CreER^T2 levels are sufficient to induce expression of the fluorescent reporters in a significant amount of cells. In contrast, only few or no fluorescent cells were observed in mTmG or R26R-EYFP retinas, indicating that those reporters recombine inefficiently under basal CreER^T2 leakage-levels. Scale bars indicate 200 μm. Right column panels: detail of the areas marked with white squares in the left panels. Scale bars indicate 50 μm. b Quantification of fluorescent cells found in the retinas of the different reporter mice (Ai14: n = 5, Ai3: n = 7, mTmG: n = 6, R26R-EYFP: n = 5). One way ANOVA was performed for statistical analysis. c Extreme example of the degree of reporter activation that can be observed under basal, non-Tamoxifen-induced, conditions using Cdh5(PAC)-CreER^T2 in combination with Ai14. The vasculature is labeled by IB4 in red, and the Ai14 reporter signal is shown in green. Scale bar indicates 500 μm