Abstract
Metaphase chromosomes of colchizinized normal human fibroblast cultures were investigated with the electron microscope.
Sections of glutaradehyde fixed and epon embedded chromosomes show 30 Å thick coiled fibrils building up folded thicker fibrils of 100–150 Å diameter.
Isolated total chromosomes pretreated in hypotonic salt solution, fixed in alcohol-acidic acid and air dried, show also 30 Å thick fibrils coiled into thicker fibrils of 200–300 Å diameter. Sections of similarly treated and epon embedded chromosomes show fibrils of similar dimensions but more loosely coiled than in glutaraldehyde fixed sections.
Major coils also seen by light microscopy are noticeable in all preparations. No signs of longitudinal subdivisions of the chromatids are detectable. In whole mount preparations the centromere region appears as less dense and kinetochores cannot be seen.
The question is discussed whether one single continuous fibril coiled to a thicker fibril which in turn is irregular folded to a strand laid into the major coils builds up a chromatid, or if many thin fibrils join together to thicker fibrils which again form thicker strands which are finally twisted together to a chromatid.
Zusammenfassung
Chromosomen von Mitosen im Metaphasestadium nach Colchicinbehandlung normaler menschlicher Fibroblastenkulturen wurden mit dem Elektronenmikroskop untersucht.
Nach Fixierung in Glutaraldehyd und Einbettung in Epon zeigen Schnittpräparate nach Kontrastierung mit Uranylacetat als feinste erkennbare Elemente etwa 30 Å dicke, schraubig gewundene Fibrillen, die dickere, vielfach und unregelmäßig gefaltete Fibrillen von 100–150 Å Durchmesser aufbauen.
Isolierte ganze Chromosomen, die zur Präparation mit hypotoner Salzlösung vorbehandelt, in Alkohol-Essigsäure fixiert und luftgetrocknet wurden, lassen stark gewundene dicke Fibrillen von 200–300 Å durchmesser erkennen, die aus schraubig gewundenen 30 Å dicken Fibrillen bestehen. In Schnittpräparaten von ähnlich vorbehandelten Chromosomen finden sich ebenfalls 200–300 Å dicke Fibrillen, die aus 30 Å dicken feineren Fibrillen in lockerer Anordnung aufgebaut sind. Der größere Durchmesser der dicken Fibrillen in hypoton vorbehandelten Präparaten könnte durch Auflockerung der feinen Fibrillen hervorgerufen sein.
In allen Präparaten sind die auch lichtmikroskopisch sichtbaren primären Windungen der Chromatiden angedeutet. Die dickeren Fibrillen lassen sonst keine regelmäßige Anordnung erkennen. Längsunterteilungen im Sinne von Halb- oder Viertelchromatiden sind nicht zu sehen. In Totalpräparaten erscheint die Region des Zentromers weniger dicht, und Kinetochoren sind nicht erkennbar.
Es wird die Frage diskutiert, ob nur eine kontinuierliche und vielfach gewundene Fibrille oder mehrere miteinander verflochtene Fibrillen und Stränge ein Chromatid aufbauen.
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Schwarzacher, H.G., Schnedl, W. Elektronenmikroskopische Untersuchungen menschlicher Metaphasen-Chromosomen. Hum Genet 4, 153–165 (1967). https://doi.org/10.1007/BF00291260
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DOI: https://doi.org/10.1007/BF00291260