title: The topology of early- and late-replicating chromatin in differentially decondensed chromosomes.
abstract: In this study we used a novel technique to reveal both longitudinal and transverse differentiation within mammalian mitotic chromosomes. Structural changes in chromosomes that we term 'differential decondensation' were produced in cells that were first incubated in hypotonic medium (15% Hanks' solution), then adapted to normotonic conditions and thereafter exposed to a second short hypotonic shock. Such a double hypotonic treatment (DHT) is not critical for cell viability, but considerably elongates the G2 phase of the cell cycle. Giemsa staining of differentially decondensed chromosomes corresponds to standard G-banding, but does not need the standard post-fixation treatment. Using 'dynamic' BrdU banding, we show that such 'differential' staining is a result of differential resistance of the R- and G-bands to DHT. Thus, early-replicating foci, markers of R-bands, are localized in the peripheral chromatin halo, whereas late-replicating foci, corresponding to G-bands, remain associated with the axial regions of chromatids. Remarkably, despite these major changes in the structure of the chromosomal bands, the replication foci still preserve their discrete structure.
authors.affiliation: Department of Electron Microscopy, A.N.Belozersky Institute of Physico-Chemical Biology, Moscow State University, 199992, Moscow, Russia.
authors.forename: Ioulia
authors.initials: I
authors.lastname: Kobliakova
authors.forename: Olga
authors.initials: O
authors.lastname: Zatsepina
authors.forename: Vera
authors.initials: V
authors.lastname: Stefanova
authors.forename: Vladimir
authors.initials: V
authors.lastname: Polyakov
authors.forename: Igor
authors.initials: I
authors.lastname: Kireev
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D002843:Chromatin / Q000502:physiology*; D002871:Chromosome Banding / Q000379:methods; D033481:Chromosomes, Mammalian / Q000187:drug effects / Q000235:genetics*; D019084:Fluorescent Antibody Technique, Indirect; D007038:Hypotonic Solutions / Q000494:pharmacology; D007668:Kidney / Q000166:cytology; D008677:Metaphase / Q000502:physiology; D008938:Mitosis / Q000502:physiology; D008957:Models, Genetic; D013552:Swine
chemical_list: D002843:Chromatin; D007038:Hypotonic Solutions