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Mol. Cell. Biol. doi:10.1128/MCB.00949-07
Copyright (c) 2008, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

CHANGES IN THE DISTRIBUTIONS AND DYNAMICS OF POLYCOMB REPRESSIVE COMPLEXES DURING EMBRYONIC STEM CELL DIFFERENTIATION

Howard Hughes Medical Institute and Department of Biological Chemistry, University of Michigan, Ann Arbor, MI 48109-0650

^* To whom correspondence should be addressed. Email: kerppola{at}umich.edu.

	Abstract

Polycomb group (PcG) transcription regulatory proteins maintain cell identity by sustained repression of numerous genes. Differentiation of embryonic stem (ES) cells induces a genome-wide shift in PcG target gene expression. We investigated the effects of differentiation and protein interactions on CBX family PcG protein localization and dynamics using fluorescence imaging. In mouse ES cells, different CBX proteins exhibited distinct distributions and mobilities. Most CBX proteins were enriched in foci known as polycomb bodies. Focus formation did not affect CBX protein mobilities, and the foci dispersed during ES cell differentiation. The mobilities of CBX proteins increased upon induction of differentiation, and decreased as differentiation progressed. Deletion of the chromobox, which mediates interactions with RING1B, prevented the immobilization of CBX proteins. In contrast, deletion of the chromodomain, which can bind trimethylated lysine 27 of histone H3, had little effect on CBX protein dynamics. The distributions and mobilities of most CBX proteins corresponded to those of CBX-RING1B complexes detected using bimolecular fluorescence complementation (BiFC) analysis. Epigenetic reprogramming during ES cell differentiation is therefore associated with global changes in the subnuclear distributions and dynamics of CBX protein complexes.