The developmental emergence and stem cell-based renewal of the intestinal telocyte niche
The intestinal telocytes that reside beneath the intestinal epithelium exert niche-supporting roles for intestinal stem cells (ISCs) and their progenies. They are heterogenous cells compartmentalized along the crypt-villus axis, but the lineage relationships and mechanisms governing the maintenance of this telocyte population remain poorly understood. Through single cell analysis of mouse small intestine development, here we identify a distinct subset of Foxl1+ mesenchymal cells marked by LIM Domain Only 3 (Lmo3), whose emergence at embryonic day E13.5-14.5 precedes the initiation of villus morphogenesis and the appearance of Lgr5+ ISCs. Later on, these villus-associated telocytes undergo proliferation and expansion, extending their presence to both villus and intervillus regions. After birth, the distribution of the Lmo3+ telocytes gradually becomes confined to the isthmus region, where they persist as long-lived cells and slowly give rise to the progenies that migrate either up- or down-wards and differentiate into villus- or crypt-associated telocytes, respectively. The Lmo3+ cells are responsive to intestinal damage and ablation of these cells compromises the epithelial repair process. Thus, the Lmo3+ cells residing in the isthmus region of the adult small intestine represent a population of telocyte stem cells (TeloSCs) that regulate telocyte niche homeostasis and regeneration. The single cell delineation of the ISC niche emergence and the discovery of TeloSCs open up new avenues for understanding the roles of the mesenchymal environment in intestinal development and diseases. Overall design: Embryonic mouse samples were obtained from timed mating. E0.5d was defined as the morning of the day when the copulatory plug was observed. For embryonic (E12.5d, E13.5d, E14.5d, and E15.5d) samples, several small intestines from many mice were mixed in tissue pooling due to the small sample size, with living cells collected through FACS (Biorad). For the E19.5d samples, small intestines were collected from the middle region of the small intestine from individual mice. For Lmo3_E19.5 samples, Lmo3-CreERT2;Ai6 mice were injected with 120mg/kg tamoxifen each day for three days (E13.5-E15.5), small intestines were then sampled at E19.5d collectively from gravid mice after euthanasia and ZsGreen1+ cells were collected through FACS.