title: In vivo Polycomb kinetics and mitotic chromatin binding distinguish stem cells from differentiated cells.
abstract: Epigenetic memory mediated by Polycomb group (PcG) proteins must be maintained during cell division, but must also be flexible to allow cell fate transitions. Here we quantify dynamic chromatin-binding properties of PH::GFP and PC::GFP in living Drosophila in two cell types that undergo defined differentiation and mitosis events. Quantitative fluorescence recovery after photobleaching (FRAP) analysis demonstrates that PcG binding has a higher plasticity in stem cells than in more determined cells and identifies a fraction of PcG proteins that binds mitotic chromatin with up to 300-fold longer residence times than in interphase. Mathematical modeling examines which parameters best distinguish stem cells from differentiated cells. We identify phosphorylation of histone H3 at Ser 28 as a potential mechanism governing the extent and rate of mitotic PC dissociation in different lineages. We propose that regulation of the kinetic properties of PcG-chromatin binding is an essential factor in the choice between stability and flexibility in the establishment of cell identities.
authors.affiliation: Institute of Molecular Biotechnology, Vienna, Austria.
authors.forename: João Pedro
authors.initials: JP
authors.lastname: Fonseca
authors.forename: Philipp A
authors.initials: PA
authors.lastname: Steffen
authors.forename: Stefan
authors.initials: S
authors.lastname: Müller
authors.forename: James
authors.initials: J
authors.lastname: Lu
authors.forename: Anna
authors.initials: A
authors.lastname: Sawicka
authors.forename: Christian
authors.initials: C
authors.lastname: Seiser
authors.forename: Leonie
authors.initials: L
authors.lastname: Ringrose
mesh_terms: D000818:Animals; D002454:Cell Differentiation; D002843:Chromatin / Q000378:metabolism*; D029721:Drosophila Proteins / Q000378:metabolism; D004331:Drosophila melanogaster / Q000166:cytology; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000378:metabolism; D006657:Histones / Q000378:metabolism; D008938:Mitosis; D008954:Models, Biological; D010766:Phosphorylation; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology* / Q000378:metabolism
chemical_list: D002843:Chromatin; D029721:Drosophila Proteins; D006657:Histones; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; D049452:Green Fluorescent Proteins; D012694:Serine