Characterization of the Two Inducible Cre Recombinase-Based Mouse Models NG2-CreER (TM) and PDGFRb-P2A-CreER(T2) for Pericyte Labeling in the Retina

Purpose Pericytes (PCs), located abluminal of endothelial cells on capillaries, are essential for vascular development and stability. They display a heterogeneous morphology depending on organ localization, differentiation state, and function. Consequently, PCs show a diverse gene expression profile, impeding the usage of a unique PC marker and therefore the distinct identification of PCs. Inducible reporter mouse models represent an important tool for investigating the fate of PCs under physiological and pathophysiological conditions. PC-specific expression efficiency of the fluorescence reporter tdTomato following tamoxifen induction was analyzed and compared in two inducible Cre recombinase-expressing mouse models under control of the NG2 and PDGFRb promotor. Methods The NG2-CreER (TM)-tdTomato and the PDGFRb-P2A-CreER(T2)-tdTomato mice were treated with tamoxifen at three defining time points of retinal vascular development: post-natal days (P)5, P10/11/12, and P48/49/50/51. TdTomato reporter induction efficiency was determined by analyzing retinal whole mounts utilizing confocal microscopy, using the antibodies Anti-neural/glial antigen 2 (PCs), Anti-Collagen IV (basement membrane), and Anti-Glutamine Synthetase (Muller glial cells). Results Tamoxifen induction at the three different time points resulted in PC-specific expression of tdTomato in both reporter models. In the NG2-CreER (TM)-tdTomato mouse, the induction efficiency ranged from 21.9 to 35.5%. In the PDGFRb-P2A-CreER(T2)-tdTomato mouse, an induction efficiency between 78.9 and 94.1% was achieved. TdTomato expression in the retina was restricted to PCs and vascular smooth muscle cells in the NG2-CreER (TM)-tdTomato mouse, however, in the PDGFRb-P2A-CreER(T2)-tdTomato mouse, tdTomato was also expressed in Muller glial cells. Conclusion Both reporter mouse models represent promising tools for fate-mapping studies of PCs. While the NG2-CreER (TM)-tdTomato mouse reveals very specific labeling of PCs in the retina, its induction efficiency is lower compared to the PDGFRb-P2A-CreER(T2)-tdTomato mouse. Although the latter revealed a high percentage of tdTomato-positive PCs in the retina, additional labeling of Muller cells potentially hampers analysis of reporter-positive PCs.