title: Redundant sources of Wnt regulate intestinal stem cells and promote formation of Paneth cells.
abstract: OBJECTIVE
  Wnt signaling regulates multiple aspects of intestinal physiology, including stem cell maintenance. Paneth cells support stem cells by secreting Wnt, but little is known about the exact sources and primary functions of individual Wnt family members.
  
  
  METHODS
  We analyzed intestinal tissues and cultured epithelial cells from adult mice with conditional deletion of Wnt3 (Vil-CreERT2;Wnt3fl/fl mice). We also analyzed intestinal tissues and cells from Atoh1 mutant mice, which lack secretory cells.
  
  
  RESULTS
  Unexpectedly, Wnt3 was dispensable for maintenance of intestinal stem cells in mice, indicating a redundancy of Wnt signals. By contrast, cultured crypt organoids required Paneth cell-derived Wnt3. Addition of exogenous Wnt, or coculture with mesenchymal cells, restored growth of Vil-CreERT2;Wnt3fl/fl crypt organoids. Intestinal organoids from Atoh1 mutant mice did not grow or form Paneth cells; addition of Wnt3 allowed growth in the absence of Paneth cells. Wnt signaling had a synergistic effect with the Lgr4/5 ligand R-spondin to induce formation of Paneth cells. Mosaic expression of Wnt3 in organoids using a retroviral vector promoted differentiation of Paneth cells in a cell-autonomous manner.
  
  
  CONCLUSIONS
  Wnt is part of a signaling loop that affects homeostasis of intestinal stem and Paneth cells in mice. Wnt3 signaling is required for growth and development of organoid cultures, whereas nonepithelial Wnt signals could provide a secondary physiological source of Wnt.
authors.affiliation: Hubrecht Institute for Developmental Biology and Stem Cell Research and University Medical Centre Utrecht, Utrecht, The Netherlands.
authors.forename: Henner F
authors.initials: HF
authors.lastname: Farin
authors.forename: Johan H
authors.initials: JH
authors.lastname: Van Es
authors.forename: Hans
authors.initials: H
authors.lastname: Clevers
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology*; D002478:Cells, Cultured; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D006706:Homeostasis / Q000502:physiology; D066298:In Vitro Techniques; D007421:Intestine, Small / Q000166:cytology* / Q000502:physiology; D051379:Mice; D008822:Mice, Transgenic; D023421:Models, Animal; D019879:Paneth Cells / Q000166:cytology* / Q000502:physiology; D015398:Signal Transduction / Q000502:physiology; D013234:Stem Cells / Q000166:cytology* / Q000502:physiology; D060508:Wnt3 Protein / Q000502:physiology*
chemical_list: D060508:Wnt3 Protein; C555508:Wnt3 protein, mouse