title: BMI1 represses Ink4a/Arf and Hox genes to regulate stem cells in the rodent incisor.
abstract: The polycomb group gene Bmi1 is required for maintenance of adult stem cells in many organs. Inactivation of Bmi1 leads to impaired stem cell self-renewal due to deregulated gene expression. One critical target of BMI1 is Ink4a/Arf, which encodes the cell-cycle inhibitors p16(Ink4a) and p19(Arf). However, deletion of Ink4a/Arf only partially rescues Bmi1-null phenotypes, indicating that other important targets of BMI1 exist. Here, using the continuously growing mouse incisor as a model system, we report that Bmi1 is expressed by incisor stem cells and that deletion of Bmi1 resulted in fewer stem cells, perturbed gene expression and defective enamel production. Transcriptional profiling revealed that Hox expression is normally repressed by BMI1 in the adult, and functional assays demonstrated that BMI1-mediated repression of Hox genes preserves the undifferentiated state of stem cells. As Hox gene upregulation has also been reported in other systems when Bmi1 is inactivated, our findings point to a general mechanism whereby BMI1-mediated repression of Hox genes is required for the maintenance of adult stem cells and for prevention of inappropriate differentiation.
authors.affiliation: Department of Orofacial Sciences and Program in Craniofacial and Mesenchymal Biology, University of California San Francisco, San Francisco, California 94143, USA.
authors.forename: Brian
authors.initials: B
authors.lastname: Biehs
authors.forename: Jimmy Kuang-Hsien
authors.initials: JK
authors.lastname: Hu
authors.forename: Nicolas B
authors.initials: NB
authors.lastname: Strauli
authors.forename: Eugenio
authors.initials: E
authors.lastname: Sangiorgi
authors.forename: Heekyung
authors.initials: H
authors.lastname: Jung
authors.forename: Ralf-Peter
authors.initials: RP
authors.lastname: Heber
authors.forename: Sunita
authors.initials: S
authors.lastname: Ho
authors.forename: Alice F
authors.initials: AF
authors.lastname: Goodwin
authors.forename: Jeremy S
authors.initials: JS
authors.lastname: Dasen
authors.forename: Mario R
authors.initials: MR
authors.lastname: Capecchi
authors.forename: Ophir D
authors.initials: OD
authors.lastname: Klein
mesh_terms: D020727:ADP-Ribosylation Factors / Q000502:physiology*; D000818:Animals; D002454:Cell Differentiation; D002478:Cells, Cultured; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000502:physiology*; D003743:Dental Enamel / Q000166:cytology* / Q000378:metabolism; D005801:Genes, Homeobox / Q000502:physiology*; D007180:Incisor / Q000166:cytology* / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D063150:Polycomb Repressive Complex 1 / Q000502:physiology*; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism
chemical_list: C489421:Bmi1 protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D011518:Proto-Oncogene Proteins; D063150:Polycomb Repressive Complex 1; D020727:ADP-Ribosylation Factors