Cbx2 stably associates with mitotic chromosomes via a PRC2- or PRC1-independent mechanism and is needed for recruiting PRC1 complex to mitotic chromosomes.
Bottom Line: 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.
Affiliation: Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364.Show MeSH
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Mentions: To test whether the Cbx2 interaction with Ring1b is required for the recruitment of Ring1b protein to mitotic chromosomes, the three fusion proteins mCherry-H2A, Cerulean-Ring1b, and YFP-Cbx21-498 were expressed in Cbx2 KO ES cells. The YFP-Cbx21-498 fusion protein lacks the chromobox (Cbox) domain required for interaction with Ring1b (Satijn et al., 1997; Schoorlemmer et al., 1997; Bardos et al., 2000). We expected that the Cbx2 mutant fusion protein would not be able to recruit Cerulean-Ring1b to mitotic chromosomes. Quantitative image analysis showed that (92 ± 7)% of YFP-Cbx21-498 fusion protein accumulated at mitotic chromosomes, indicating the deletion of the Cbox domain of Cbx2 protein does not affect its mitotic chromosomal association (Figure 4, B and C; also see later discussion of Figure 7B). However, only (32 ± 8)% of Cerulean-Ring1b fusion protein associated with mitotic chromosomes (Figure 4, B and D). The fraction of mitotic retention of Ringb1b fusion protein in Cbx2 KO ES cell lines complemented with Cbx21-498 was similar to that observed in Cbx2 KO ES cells. These data indicate that the Cbx2 interaction with Ring1b is required for the recruitment of Cerulean-Ring1b fusion protein to mitotic chromosomes.
Affiliation: Department of Chemistry, University of Colorado Denver, Denver, CO 80217-3364.