Title :

Electron Tomography of Metaphase Nucleolar Organizer Regions: Evidence for a Twisted-Loop Organization

Author(s) :

Héliot, Laurent [Auteur]
Laboratoire de Physique des Lasers, Atomes et Molécules - UMR 8523 [PhLAM]
Kaplan, Hervé [Auteur]
Lucas, Laurent [Auteur]
Centre de Recherche en Sciences et Technologies de l'Information et de la Communication - EA 3804 [CRESTIC]
Klein, Christophe [Auteur]
Beorchia, Adrien [Auteur]
Doco-Fenzy, Martine [Auteur]
Menager, Monique [Auteur]
Thiry, Marc [Auteur]
Centre Hospitalier Universitaire Sart Tilman [CHU Sart Tilman]
Ploton, Dominique [Auteur]
O'Donohue, Marie-Françoise [Auteur]

Journal title :

Molecular Biology of the Cell

Pages :

2199-2216

Publisher :

American Society for Cell Biology

Publication date :

1997-11

HAL domain(s) :

Sciences du Vivant [q-bio]
Sciences du Vivant [q-bio]/Biologie cellulaire

English abstract : [en]

Metaphase nucleolar organizer regions (NORs), one of four types of chromosome bands, are located on human acrocentric chromosomes. They contain r-chromatin, i.e., ribosomal genes complexed with proteins such as upstream ...
Show more >Metaphase nucleolar organizer regions (NORs), one of four types of chromosome bands, are located on human acrocentric chromosomes. They contain r-chromatin, i.e., ribosomal genes complexed with proteins such as upstream binding factor and RNA polymerase I, which are argyrophilic NOR proteins. Immunocytochemical and cytochemical labelings of these proteins were used to reveal r-chromatin in situ and to investigate its spatial organization within NORs by confocal microscopy and by electron tomography. For each labeling, confocal microscopy revealed small and large double-spotted NORs and crescent-shaped NORs. Their internal three-dimensional (3D) organization was studied by using electron tomography on specifically silver-stained NORs. The 3D reconstructions allow us to conclude that the argyrophilic NOR proteins are grouped as a fiber of 60-80 nm in diameter that constitutes either one part of a turn or two or three turns of a helix within small and large double-spotted NORs, respectively. Within crescent-shaped NORs, virtual slices reveal that the fiber constitutes several longitudinally twisted loops, grouped as two helical 250- to 300-nm coils, each centered on a nonargyrophilic axis of condensed chromatin. We propose a model of the 3D organization of r-chromatin within elongated NORs, in which loops are twisted and bent to constitute one basic chromatid coil.Show less >

Language :

Anglais

Peer reviewed article :

Oui

Audience :

Internationale

Popular science :

Non

Collections :

• Laboratoire de Physique des Lasers, Atomes et Molécules (PhLAM) - UMR 8523

Source :

Harvested from HAL