title: Polycomb gene product Bmi-1 regulates stem cell self-renewal.
abstract: The Polycomb group (PcG) gene Bmi-1 has recently been implicated in the maintenance of hematopoietic stem cells (HSCs). However, the role of each component of PcG complex in HSCs and the impact of forced expression of PcG genes on stem cell self-renewal remain to be elucidated. To address these issues, we performed both loss-of-function and gain-of-function analysis on various PcG proteins. Expression analysis revealed that not only Bmi-1 but also other PcG genes are predominantly expressed in HSCs. Loss-of-function analyses, however, demonstrated that absence of Bmi-1 is preferentially linked with a profound defect in HSC self-renewal, indicating a central role for Bmi-1, but not the other components, in the maintenance of HSC self-renewal. Over-expression analysis of PcG genes also confirmed an important role of Bmi-1 in HSC self-renewal. Our findings indicate that the expression level of Bmi-1 is the critical determinant for the self-renewal capacity of HSCs. These findings uncover novel aspects of stem cell regulation exerted through epigenetic modifications by the PcG proteins.
authors.affiliation: Laboratory of Stem Cell Therapy, Center for Experimental Medicine, Institute of Medical Science, University of Tokyo, Japan.
authors.forename: H
authors.initials: H
authors.lastname: Nakauchi
authors.forename: H
authors.initials: H
authors.lastname: Oguro
authors.forename: M
authors.initials: M
authors.lastname: Negishi
authors.forename: A
authors.initials: A
authors.lastname: Iwama
mesh_terms: D000818:Animals; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division / Q000502:physiology*; D051379:Mice; D009687:Nuclear Proteins / Q000502:physiology*; D063150:Polycomb Repressive Complex 1; D011518:Proto-Oncogene Proteins / Q000502:physiology*; D012097:Repressor Proteins / Q000502:physiology*; D013234:Stem Cells / Q000166:cytology*
chemical_list: C489421:Bmi1 protein, mouse; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; D012097:Repressor Proteins; D063150:Polycomb Repressive Complex 1