Lgr5+ Gastric Stem Cells Divide Symmetrically to Effect Epithelial Homeostasis in the Pylorus

The pyloric epithelium continuously self-renews throughout life, driven by limited reservoirs of resident Lgr5(+) adult stem cells. Here, we characterize the population dynamics of these stem cells during epithelial homeostasis. Using a clonal fate-mapping strategy, we demonstrate that multiple Lgr5(+) cells routinely contribute to epithelial renewal in the pyloric gland and, similar to what was previously observed in the intestine, a balanced homeostasis of the glandular epithelium and stem cell pools is predominantly achieved via neutral competition between symmetrically dividing Lgr5(+) stem cells. Additionally, we document a lateral expansion of stem cell clones via gland fission under nondamage conditions. These findings represent a major advance in our basic understanding of tissue homeostasis in the stomach and form the foundation for identifying altered stem cell behavior during gastric disease.