title: Depletion of the colonic epithelial precursor cell compartment upon conditional activation of the hedgehog pathway.
abstract: OBJECTIVE
  The intestinal epithelium is a homeostatic system in which differentiated cells are in dynamic equilibrium with rapidly cycling precursor cells. Wnt signaling regulates intestinal epithelial precursor cell fate and proliferation. Homeostatic systems exist by virtue of negative feedback loops, and we have previously identified the Hedgehog (Hh) pathway as a potential negative feedback signal in the colonic epithelium. Indian hedgehog (Ihh) is produced by the differentiated enterocytes and negatively regulates Wnt signaling in intestinal precursor cells. We studied the role of members of the Hh signaling family in the intestine using a conditional genetic approach.
  
  
  METHODS
  We inactivated the Hh receptor Patched1 (Ptch1) in adult mice, resulting in constitutive activation of the Hh signaling pathway. Effects on colonic mucosal homeostasis were examined. Colon tissues were examined by immunohistochemistry, in situ hybridization, transmission electron microscopy, and real-time polymerase chain reaction.
  
  
  RESULTS
  Ihh but not Sonic hedgehog (Shh) was expressed in colonic epithelium. Expression of Ptch1 and Gli1 was restricted to the mesenchyme. Constitutive activation of Hh signaling resulted in accumulation of myofibroblasts and colonic crypt hypoplasia. A reduction in the number of epithelial precursor cells was observed with premature development into the enterocyte lineage and inhibition of Wnt signaling. Activation of Hh signaling resulted in induction of the expression of bone morphogenetic proteins (Bmp) and increased Bmp signaling in the epithelium.
  
  
  CONCLUSIONS
  Hh signaling acts in a negative feedback loop from differentiated cells via the mesenchyme to the colonic epithelial precursor cell compartment in the adult mouse.
authors.affiliation: Center for Experimental Molecular Medicine, Academic Medical Center, Amsterdam, The Netherlands. w.a.vandop@amc.uva.nl
authors.forename: Willemijn A
authors.initials: WA
authors.lastname: van Dop
authors.forename: Anja
authors.initials: A
authors.lastname: Uhmann
authors.forename: Mark
authors.initials: M
authors.lastname: Wijgerde
authors.forename: Esther
authors.initials: E
authors.lastname: Sleddens-Linkels
authors.forename: Jarom
authors.initials: J
authors.lastname: Heijmans
authors.forename: G Johan
authors.initials: GJ
authors.lastname: Offerhaus
authors.forename: Marius A
authors.initials: MA
authors.lastname: van den Bergh Weerman
authors.forename: Guy E
authors.initials: GE
authors.lastname: Boeckxstaens
authors.forename: Daan W
authors.initials: DW
authors.lastname: Hommes
authors.forename: James C
authors.initials: JC
authors.lastname: Hardwick
authors.forename: Heidi
authors.initials: H
authors.lastname: Hahn
authors.forename: Gijs R
authors.initials: GR
authors.lastname: van den Brink
mesh_terms: D000818:Animals; D019485:Bone Morphogenetic Proteins / Q000235:genetics / Q000378:metabolism; D049109:Cell Proliferation; D002478:Cells, Cultured; D003106:Colon / Q000166:cytology / Q000378:metabolism / Q000473:pathology*; D004847:Epithelial Cells / Q000166:cytology / Q000502:physiology; D018507:Gene Expression Regulation, Developmental; D053823:Hedgehog Proteins / Q000235:genetics / Q000378:metabolism*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D007413:Intestinal Mucosa / Q000166:cytology / Q000473:pathology*; D051379:Mice; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission; D023421:Models, Animal; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012680:Sensitivity and Specificity; D015398:Signal Transduction / Q000235:genetics / Q000502:physiology*; D051153:Wnt Proteins / Q000235:genetics / Q000378:metabolism
chemical_list: D019485:Bone Morphogenetic Proteins; D053823:Hedgehog Proteins; D051153:Wnt Proteins