Stem/progenitor cell dynamics during salivary gland development and regeneration demonstrated by the double pulse-chase paradigm

Introduction: Active and quiescent stem cells coexist in hair follicles and intestinal crypts; however, their localization and differentiation potential in the salivary dynamics are unknown. This study aimed to clarify the cellular dynamics that occur during salivary gland development and regeneration in the duct ligation model with a focus on the role of label retaining cells (LRCs), presumably quiescent stem cells, in these processes. Methods: Doxycycline-inducible TetOP-histone 2B (H2B)-green fluorescent protein (GFP) transgenic mice [GFP expression was induced during embryonic day 15 (E15)–postnatal day 7 (P7)] followed by EdU (5-ethynyl-2′-deoxyuridine) administration at P10–14 to chase the LRCs during development. In addition, LRCs were labeled with GFP immediately before salivary gland duct ligation and EdU was administered after the ligation was released to chase the LRCs with GFP and EdU during tissue repair. Results and conclusions: During development, GFP (+) EdU (−) LRCs were abundant in striated duct cells (SDCs) and GFP (+) EdU (+) LRCs were primarily localized to the intercalated duct cells (IDCs) at P21. Labeling of the GFP (+) LRCs faded as well as the EdU (+) LRCs at P70. During tissue repair, GFP (+) EdU (+) LRCs were colocalized in the IDCs and myoepithelium cells (MECs), whereas the GFP (+) EdU (+) acinar cells (ACs) appeared over time. These results suggest that salivary gland quiescent stem/progenitor cells are present in the IDCs during development and that quiescent stem/progenitor cells in the IDCs and MECs differentiate into ACs during tissue repair.