Cell Stem Cell Short Article Poised Lineage Specification in Multipotential Hematopoietic Stem and Progenitor Cells by the Polycomb Protein Bmi1 Hideyuki Oguro,1,2 Jin Yuan,1,2 Hitoshi Ichikawa,4 Tomokatsu Ikawa,5 Satoshi Yamazaki,3,6 Hiroshi Kawamoto,5 Hiromitsu Nakauchi,3,6 and Atsushi Iwama1,2,* 1Department of Cellular and Molecular Medicine, Graduate School of Medicine, Chiba University, Chiba 260-8670, Japan 2JST, CREST 3JST, ERATO Sanbancho, Chiyoda-ku, Tokyo 102-0075, Japan 4Genetics Division, National Cancer Center Research Institute, Tokyo, 104-0045, Japan 5Laboratory for Lymphocyte Development, RIKEN Research Center for Allergy and Immunology, Yokohama 230-0045, Japan 6Laboratory of Stem Cell Therapy, Center for Experimental Medicine, Institute of Medical Sciences, University of Tokyo, Tokyo 108-8679, Japan *Correspondence:
[email protected] DOI 10.1016/j.stem.2010.01.005 SUMMARY Pietersen and van Lohuizen, 2008). They reside in two main complexes, termed Polycomb repressive complex 1 and 2 Polycomb group (PcG) proteins are essential regula- (PRC1 and PRC2). PRC2 and trithorax group (trxG) proteins tors of stem cells. PcG and trithorax group proteins mark developmental regulator gene promoters with bivalent mark developmental regulator gene promoters with domains consisting of overlapping repressive and activating bivalent domains consisting of overlapping repres- histone modifications to keep developmental regulators sive and activating histone modifications to keep ‘‘poised’’ for activation in embryonic stem cells (ESCs) (Bernstein them poised for activation in embryonic stem cells. et al., 2006; Spivakov and Fisher 2007; Mendenhall and Bern- stein, 2008). Likewise, in adult stem cells, developmental regula- Bmi1, a component of PcG complexes, maintains tors that govern lineage specification are supposedly repressed the self-renewal capacity of adult stem cells, but its epigenetically to maintain their multipotency (Pietersen and van role in multipotency remains obscure.