Characterization of the Two Inducible Cre Recombinase-Based Mouse Models NG2-CreER™ and PDGFRb-P2A-CreERT2 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.

Automated summary

Pericytes (PCs) play a crucial role in vascular development and stability. In this study, two inducible reporter mouse models were used to investigate the expression efficiency of the tdTomato reporter gene in PCs. The results showed that both models successfully labeled PCs, but with different induction efficiencies. These models represent promising tools for fate-mapping studies of PCs, although one model showed additional labeling of Muller cells, which may hinder the analysis of reporter-positive PCs.