Tissues that undergo rapid cellular turnover, such as the mammalian haematopoietic system or the intestinal epithelium, are dependent on stem and progenitor cells that proliferate to provide differentiated cells to maintain organismal health. Stem and progenitor cells, in turn, are thought to rely on signals and growth factors provided by local niche cells to support their function and self-renewal. Several cell types have been hypothesized to provide the signals required for the proliferation and differentiation of the intestinal stem cells in intestinal crypts1,2,3,4,5,6. Here we identify subepithelial telocytes as an important source of Wnt proteins, without which intestinal stem cells cannot proliferate and support epithelial renewal. Telocytes are large but rare mesenchymal cells that are marked by expression of FOXL1 and form a subepithelial plexus that extends from the stomach to the colon. While supporting the entire epithelium, FOXL1+ telocytes compartmentalize the production of Wnt ligands and inhibitors to enable localized pathway activation. Conditional genetic ablation of porcupine (Porcn), which is required for functional maturation of all Wnt proteins, in mouse FOXL1+ telocytes causes rapid cessation of Wnt signalling to intestinal crypts, followed by loss of proliferation of stem and transit amplifying cells and impaired epithelial renewal. Thus, FOXL1+ telocytes are an important source of niche signals to intestinal stem cells.
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We thank A. Rustgi, C. Lengner and Y. Dor for critical reading of the manuscript; M. Sundaram for suggesting the porcupine gene ablation experiment; and all members of the Kaestner laboratory. We acknowledge funding from NIDDK through R37-DK053839. We thank the University of Pennsylvania’s Diabetes Research Center (DRC) for the use of the Functional Genomics Core (P30-DK019525) and the Center for Molecular Studies in Digestive and Liver Diseases for the use of the Molecular Pathology and Imaging and Transgenic and Chimeric Mouse Cores (P30-DK050306).Reviewer information
Nature thanks L. Samuelson and the other anonymous reviewer(s) for their contribution to the peer review of this work.
Extended data figures and tables
a–d, Representative FACS plots of mesenchymal cells isolated from Foxl1-cre;Rosa26-mTmG (c, d) as compared to control Rosa26-mTmG (a, b) mice, showing sorting strategy. In a and c, Allophycocyanin+ (APC+), CD45+ and EPCAM+-labelled cells were gated out to exclude immune and epithelial cell contamination. In d, FOXL1+, GFP+ and FOXL1−Tomato+ cells were gated and sorted based on fluorescence activity as compared to the negative control (b). Experiments were repeated at least three times with similar results.
Extended Data Fig. 2 Single-cell qPCR of FOXL1+ telocytes showing heterogeneity within the FOXL1+ cell population.
Hierarchical clustering of FOXL1+ single cells based on qPCR-based detection of 30 genes. Note that all FOXL1+ cells express Pdgfra and Wnt3a. The population is clustered into three main groups. Jaccard coefficients for the three clusters were: 0.83 (green), 0.69 (turquoise) and 0.79 (yellow), respectively, indicating underlying cluster stability. Values between 0.6 and 0.75 indicate that the cluster is measuring a pattern in the data. Clusters with stability values above about 0.85 are considered to be highly stable.
a, Schema for the generation of Foxl1-creERT2 mice using BAC recombineering. The coding sequence of exon 1 of Foxl1 was targeted by the sequence of creERT2. FRT, flipase recognition target; Flp, flipase; LA, left homology arm; RA, right homology arm. b, c, Tamoxifen induction of Foxl1-creERT2;Rosa26-mTmG-driven expression of membrane-bound GFP to mesenchymal telocytes in the duodenum (b) and colon (c). Immunofluorescence staining for GFP (green), EPCAM (red). d, Schema for the generation of Foxl1-creERT2;PorcnΔ mice. Foxl1-creERT2 mice were crossed with mice carrying loxP sites flanking exons 3–7 of the X-linked porcupine homologue (Porcn) gene. e, Foxl1-creERT2;Rosa26-mTmG (control, n = 5 mice) and Foxl1-creERT2;PorcnΔ (PorcnΔ, n = 8 mice) male mice were treated with tamoxifen for three consecutive days to induce Cre expression and weighed every day. The slope of the weight loss was significantly different in PorcnΔ mice as compared to control mice (*P = 0.0107, two-tailed linear regression analysis).
Foxl1+ telocytes form a continuous subepithelial network from crypt base to villus tips. Confocal 3D projection of cleared duodenum from Foxl1Cre; Rosa-mTmG mouse stained with GFP (green), EpCAM (red) and DAPI. Image width is 1.2 mm. The stained intestine was placed en block on an image slide using 1 mm depth adhesive silicone isolator, mounted in X-CLARITYTM mounting solution and imaged using confocal scanning. Z-stacks projections were compiled using Volocity software