Jr. Abney et al., CHROMATIN DYNAMICS IN INTERPHASE NUCLEI AND ITS IMPLICATIONS FOR NUCLEAR-STRUCTURE, The Journal of cell biology, 137(7), 1997, pp. 1459-1468
Translational dynamics of chromatin in interphase nuclei of living Swi
ss 3T3 and HeLa cells was studied using fluorescence microscopy and fl
uorescence recovery after photobleaching. Chromatin was fluorescently
labeled using dihydroethidium, a membrane-permeant derivative of ethid
ium bromide. After labeling, a laser was used to bleach small (similar
to 0.4 mu m radius) spots in the heterochromatin and euchromatin of c
ells of both types. These spots were observed to persist for >1 h, imp
lying that interphase chromatin is immobile over distance scales great
er than or equal to 0.4 mu m. Over very short times (<1 s), a partial
fluorescence recovery within the spots was observed. This partial reco
very is attributed to independent dye motion, based on comparison with
results obtained using ethidium homodimer-1, which binds essentially
irreversibly to nucleic acids. The immobility observed here is consist
ent with chromosome confinement to domains in interphase nuclei. This
immobility may reflect motion-impeding steric interactions that arise
in the highly concentrated nuclear milieu or outright attachment of th
e chromatin to underlying nuclear substructures, such as nucleoli, the
nuclear lamina, or the nuclear matrix.