title: Cbx2 stably associates with mitotic chromosomes via a PRC2- or PRC1-independent mechanism and is needed for recruiting PRC1 complex to mitotic chromosomes.
abstract: Polycomb group (PcG) proteins are epigenetic transcriptional factors that repress key developmental regulators and maintain cellular identity through mitosis via a poorly understood mechanism. Using quantitative live-cell imaging in mouse ES cells and tumor cells, we demonstrate that, although Polycomb repressive complex (PRC) 1 proteins (Cbx-family proteins, Ring1b, Mel18, and Phc1) exhibit variable capacities of association with mitotic chromosomes, Cbx2 overwhelmingly binds to mitotic chromosomes. The recruitment of Cbx2 to mitotic chromosomes is independent of PRC1 or PRC2, and Cbx2 is needed to recruit PRC1 complex to mitotic chromosomes. Quantitative fluorescence recovery after photobleaching analysis indicates that PRC1 proteins rapidly exchange at interphasic chromatin. On entry into mitosis, Cbx2, Ring1b, Mel18, and Phc1 proteins become immobilized at mitotic chromosomes, whereas other Cbx-family proteins dynamically bind to mitotic chromosomes. Depletion of PRC1 or PRC2 protein has no effect on the immobilization of Cbx2 on mitotic chromosomes. We find that the N-terminus of Cbx2 is needed for its recruitment to mitotic chromosomes, whereas the C-terminus is required for its immobilization. Thus these results provide fundamental insights into the molecular mechanisms of epigenetic inheritance.
authors.affiliation: Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364.
authors.forename: Chao Yu
authors.initials: CY
authors.lastname: Zhen
authors.affiliation: Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364.
authors.forename: Huy Nguyen
authors.initials: HN
authors.lastname: Duc
authors.affiliation: Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364.
authors.forename: Marko
authors.initials: M
authors.lastname: Kokotovic
authors.affiliation: Department of Integrative Biology, University of Colorado Denver, Denver, CO 80217-3364.
authors.forename: Christopher J
authors.initials: CJ
authors.lastname: Phiel
authors.affiliation: Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364 xiaojun.ren@ucdenver.edu.
authors.forename: Xiaojun
authors.initials: X
authors.lastname: Ren
mesh_terms: D000818:Animals; D002843:Chromatin / Q000235:genetics; D002875:Chromosomes / Q000235:genetics; D053595:Embryonic Stem Cells / Q000166:cytology / Q000378:metabolism; D044127:Epigenesis, Genetic / Q000235:genetics*; D051379:Mice; D008938:Mitosis / Q000235:genetics; D063150:Polycomb Repressive Complex 1 / Q000235:genetics* / Q000378:metabolism; D063146:Polycomb-Group Proteins / Q000235:genetics; D044767:Ubiquitin-Protein Ligases / Q000235:genetics
chemical_list: C570426:Cbx2 protein, mouse; D002843:Chromatin; C066476:Pcgf6 protein, mouse; C103827:Phc1 protein, mouse; D063146:Polycomb-Group Proteins; D063150:Polycomb Repressive Complex 1; C489842:Rnf2 protein, mouse; D044767:Ubiquitin-Protein Ligases