title: Differential impact of Ink4a and Arf on hematopoietic stem cells and their bone marrow microenvironment in Bmi1-deficient mice.
abstract: The polycomb group (PcG) protein Bmi1 plays an essential role in the self-renewal of hematopoietic and neural stem cells. Derepression of the Ink4a/Arf gene locus has been largely attributed to Bmi1-deficient phenotypes in the nervous system. However, its role in hematopoietic stem cell (HSC) self-renewal remained undetermined. In this study, we show that derepressed p16(Ink4a) and p19(Arf) in Bmi1-deficient mice were tightly associated with a loss of self-renewing HSCs. The deletion of both Ink4a and Arf genes substantially restored the self-renewal capacity of Bmi1(-/-) HSCs. Thus, Bmi1 regulates HSCs by acting as a critical failsafe against the p16(Ink4a)- and p19(Arf)-dependent premature loss of HSCs. We further identified a novel role for Bmi1 in the organization of a functional bone marrow (BM) microenvironment. The BM microenvironment in Bmi1(-/-) mice appeared severely defective in supporting hematopoiesis. The deletion of both Ink4a and Arf genes did not considerably restore the impaired BM microenvironment, leading to a sustained postnatal HSC depletion in Bmi1(-/-)Ink4a-Arf(-/-) mice. Our findings unveil a differential role of derepressed Ink4a and Arf on HSCs and their BM microenvironment in Bmi1-deficient mice. Collectively, Bmi1 regulates self-renewing HSCs in both cell-autonomous and nonautonomous manners.
authors.affiliation: Laboratory of Stem Cell Therapy, Center for Experimental Medicine, Institute of Medical Sciences, University of Tokyo, Tokyo 108-8679, Japan.
authors.forename: Hideyuki
authors.initials: H
authors.lastname: Oguro
authors.forename: Atsushi
authors.initials: A
authors.lastname: Iwama
authors.forename: Yohei
authors.initials: Y
authors.lastname: Morita
authors.forename: Takehiko
authors.initials: T
authors.lastname: Kamijo
authors.forename: Maarten
authors.initials: M
authors.lastname: van Lohuizen
authors.forename: Hiromitsu
authors.initials: H
authors.lastname: Nakauchi
mesh_terms: D000818:Animals; D001853:Bone Marrow / Q000378:metabolism*; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000378:metabolism*; D017931:DNA Primers; D006412:Hematopoietic Stem Cells / Q000166:cytology*; D051379:Mice; D008817:Mice, Mutant Strains; D009687:Nuclear Proteins / Q000172:deficiency*; D063150:Polycomb Repressive Complex 1; D011518:Proto-Oncogene Proteins / Q000172:deficiency*; D012097:Repressor Proteins; D020133:Reverse Transcriptase Polymerase Chain Reaction
chemical_list: C069077:BMI1 protein, human; C417743:Cdkn2a protein, mouse; D019941:Cyclin-Dependent Kinase Inhibitor p16; D017931:DNA Primers; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D063150:Polycomb Repressive Complex 1