Identification and location of label retaining cells in mouse liver

Background In most somatic tissues, adult stem cells are crucial for the maintenance of tissue homeostasis under normal physiological states and during recovery from injuries. Label retaining cell (LRC) assay remains the well-known method to identify possible somatic stem/progenitor cells and their location both in situ and in vivo. Methods Here, BrdU was used to tag the possible hepatic stem/progenitor cells (HSPCs) in newborn pups, followed by a trace period of up to 23 months. Additionally, we report a method to rapidly kill proliferating cells in adult liver tissue, and activate and label (KAL) surviving possible HSPCs. Results We found that LRCs definitively exist in the liver tissues of adult mice, that LRCs express cell cycle proteins cyclind3 and cdk6, but do not express sca-1 or c-kit, and that LRCs locate primarily in the periportal and pericentral regions. Moreover, the number of these LRCs remains nearly constant during the lifespan of the mice. After injury induced by 5-fluorouracil, we observed that the activation of possible HSPCs tagged by the BrdU label was almost completely inhibited at day 4. The cellular kinetics of repair of BrdU-tagged HSPCs were different every 12 h between day 3 and day 4. Moreover, HSPCs still retained labels and located definitively in the periportal region after a prolonged chase. Conclusions The LRC method together with our novel KAL method reported here may be used to identify and locate possible HSPCs.