title: Polycomb group mutants exhibit mitotic defects in syncytial cell cycles of Drosophila embryos.
abstract: The Polycomb Group (PcG) of epigenetic regulators maintains the repressed state of Hox genes during development of Drosophila, thereby maintaining the correct patterning of the anteroposterior axis. PcG-mediated inheritance of gene expression patterns must be stable to mitosis to ensure faithful transmission of repressed Hox states during cell division. Previously, two PcG mutants, polyhomeotic and Enhancer of zeste, were shown to exhibit mitotic segregation defects in embryos, and condensation defects in imaginal discs, respectively. We show that polyhomeotic(proximal) but not polyhomeotic(distal) is necessary for mitosis. To test if other PcG genes have roles in mitosis, we examined embryos derived from heterozygous PcG mutant females for mitotic defects. Severe defects in sister chromatid segregation and nuclear fallout, but not condensation are exhibited by Polycomb, Posterior sex combs and Additional sex combs. By contrast, mutations in Enhancer of zeste (which encodes the histone methyltransferase subunit of the Polycomb Repressive Complex 2) exhibit condensation but not segregation defects. We propose that these mitotic defects in PcG mutants delay cell cycle progression. We discuss possible mitotic roles for PcG proteins, and suggest that delays in cell cycle progression might lead to failure of maintenance.
authors.affiliation: Department of Zoology, University of British Columbia, Life Sciences Centre, 2350 Health Sciences Mall, Vancouver, BC, Canada V6T 1Z3.
authors.forename: Ester
authors.initials: E
authors.lastname: O'Dor
authors.forename: Samantha A
authors.initials: SA
authors.lastname: Beck
authors.forename: Hugh W
authors.initials: HW
authors.lastname: Brock
mesh_terms: D000483:Alleles; D000818:Animals; D002453:Cell Cycle; D002467:Cell Nucleus / Q000378:metabolism; D002843:Chromatin / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D004330:Drosophila / Q000196:embryology*; D029721:Drosophila Proteins / Q000378:metabolism; D004625:Embryo, Nonmammalian / Q000378:metabolism*; D005260:Female; D018507:Gene Expression Regulation, Developmental; D015726:Giant Cells / Q000166:cytology*; D006579:Heterozygote; D007091:Image Processing, Computer-Assisted; D018613:Microscopy, Confocal; D008938:Mitosis; D009154:Mutation; D009687:Nuclear Proteins / Q000378:metabolism; D010641:Phenotype; D063151:Polycomb Repressive Complex 2; D012097:Repressor Proteins / Q000378:metabolism
chemical_list: D002843:Chromatin; D029721:Drosophila Proteins; D009687:Nuclear Proteins; D012097:Repressor Proteins; D004247:DNA; C083329:E(z) protein, Drosophila; D063151:Polycomb Repressive Complex 2