Dense chromatin plates in metaphase chromosomes
| Autor: | Juan Manuel Caravaca, Pablo Castro-Hartmann, Silvia Caño, Isaac Gállego, Joan-Ramon Daban |
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| Rok vydání: | 2009 |
| Předmět: |
Erythrocytes
Microscope Materials science Surface Properties Scanning electron microscope Biophysics Microscopy Atomic Force DNA condensation Chromosomes law.invention Protein filament Microscopy Electron Transmission law Microscopy Animals Chromosomes Human Humans Nucleosome Magnesium Lymphocytes Metaphase Cryoelectron Microscopy General Medicine Chromatin Elasticity Nucleosomes Crystallography Microscopy Electron Scanning Chickens HeLa Cells |
| Zdroj: | European Biophysics Journal. 38:503-522 |
| ISSN: | 1432-1017 0175-7571 |
| DOI: | 10.1007/s00249-008-0401-1 |
| Popis: | In a previous work we observed multilayered plate-like structures surrounding partially denatured HeLa chromosomes at metaphase ionic conditions. This unexpected finding has led us to carry out an extensive investigation of these structures. Our results show that plates can also be found in metaphase chromosomes from chicken lymphocytes. We have used atomic force microscopy (AFM) to image and investigate the mechanical properties of plates in aqueous solution. Plates are thin (approximately 6.5 nm each layer) but compact and resistant to penetration by the AFM tip: their Young's modulus is approximately 0.2 GPa and the stress required for surface penetration is approximately 0.03 GPa in the presence of Mg(2+) (5-20 mM). Low-ionic strength conditions produce emanation of chromatin fibers from the edges of uncrosslinked plates. These observations and AFM results obtained applying high forces indicate that the chromatin filament is tightly tethered inside the plates. Images of metal-shadowed plates and cryo-electron microscopy images of frozen-hydrated plates suggest that nucleosomes are tilted with respect to the plate surface to allow an interdigitation between the successive layers and a thickness reduction compatible with the observed plate height. The similarities between denatured plates from chicken chromosomes and aggregates of purified chromatin from chicken erythrocytes suggest that chromatin has intrinsic structural properties leading to plate formation. Scanning electron micrographs and images obtained with the 200-kV transmission microscope show that plates are the dominant component of compact chromatids. We propose that metaphase chromosomes are formed by many stacked plates perpendicular to the chromatid axis. |
| Databáze: | OpenAIRE |
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