Detection and Quantitation of Label-Retaining Cells in Mouse Incisors using a 3D Reconstruction Approach after Tissue Clearing

The murine incisor is an organ that grows continuously throughout the lifespan of the mouse. The epithelial and mesenchymal stem cells residing in the proximal tissues of incisors give rise to progeny that will differentiate into ameloblasts, odontoblasts, and pulp fibroblasts. These cells are crucial in supporting the sustained turnover of incisor tissues, making the murine incisor an excellent model for studying the homeostasis of adult stem cells. Stem cells are believed to contain long-living quiescent cells that can be labeled by nucleotide analogs such as 5-ethynyl-2´-deoxyuridine (EdU). The cells retain this label over time and are accordingly named label-retaining cells (LRCs). Approaches for visualizing LRCs in vivo provide a robust tool for monitoring stem cell homeostasis. In this study, we described a method for visualizing and analyzing LRCs. Our innovative approach features LRCs in mouse incisors after tissue clearing and whole-mount EdU staining followed by confocal microscopy and a 3-dimensional (3D) reconstruction with the imaging software. This method enables 3D imaging acquisition and non-biased quantitation compared to traditional LRCs analysis on sectioned slides.