title: The RNA polymerase III subunit Polr3b is required for the maintenance of small intestinal crypts in mice.
abstract: OBJECTIVE
  The continuously self-renewing mammalian intestinal epithelium, with high cellular turnover, depends on adequate protein synthesis for its proliferative capacity. RNA polymerase III activity is closely related to cellular growth and proliferation. Here, we studied the role of Polr3b, a large RNA polymerase III subunit, in the mammalian intestinal epithelium.
  
  
  METHODS
  We derived mice with an intestinal epithelium-specific hypomorphic mutation of thePolr3b gene, using VillinCre-mediated gene ablation. Phenotypic consequences of thePolr3bmutation on the intestinal epithelium in mice were assessed using histological and molecular methodologies, including genetic lineage tracing.
  
  
  RESULTS
  ThePolr3bmutation severely reduced survival and growth in mice during the first postnatal week, the period when the expansion of the intestinal epithelium, and thus the requirement for protein synthesis, are highest. The neonatal intestinal epithelium ofPolr3bloxP/loxP;VillinCremice was characterized by areas with reduced proliferation, abnormal epithelial architecture, loss of Wnt signaling and a dramatic increase in apoptotic cells in crypts. Genetic lineage tracing usingPolr3bLoxP/LoxP;Rosa26-lox-stop-lox-YFP;VillinCremice demonstrated that in surviving mutant mice, Polr3b-deficient dying crypts were progressively replaced by 'Cre-escaper' cells that had retained wild type Polr3b function. In addition, enteroids cultured fromPolr3bloxP/loxP;VillinCremice show reduced proliferative activity and increased apoptosis.
  
  
  CONCLUSIONS
  We provide evidence for an essential role of the Pol III subunit Polr3b in orchestrating the maintenance of the intestinal crypt during early postnatal development in mice.
authors.affiliation: Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia; Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Julia
authors.initials: J
authors.lastname: Kieckhaefer
authors.affiliation: Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia; Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Sabina
authors.initials: S
authors.lastname: Lukovac
authors.affiliation: Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia; Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Diana Z
authors.initials: DZ
authors.lastname: Ye
authors.affiliation: Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia; Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Dolim
authors.initials: D
authors.lastname: Lee
authors.affiliation: Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Danielle J
authors.initials: DJ
authors.lastname: Beetler
authors.affiliation: Department of Cell and Developmental Biology, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Michael
authors.initials: M
authors.lastname: Pack
authors.affiliation: Department of Genetics, University of Pennsylvania, Perelman School of Medicine, Philadelphia; Institute for Diabetes, Obesity, and Metabolism, University of Pennsylvania, Perelman School of Medicine, Philadelphia.
authors.forename: Klaus H
authors.initials: KH
authors.lastname: Kaestner
keywords: Pol III; Polr3b; crypts; enteroids; intestinal epithelium