| Abstract: | New quantitative insights on the native high order chromatin-DNA structure existing within interphase nuclei are obtained
by monitoring the effects of two common well-characterized fixatives, glutaraldehyde and ethanol/acetic acid mixture, at the
level of the intranuclear DNA distribution and structures. Reproducible distinct levels of DNA fluorescence intensity and
their intranuclear distribution are apparent in unfixed and fixed thymocytes by using DAPI and quantitative optical microscopy
based on a charge coupled device. The fluorescent histograms correlated with the calorimetric thermograms on the very same
thymocytes fixed and unfixed, establish an unequivocal baseline for the different levels of structural organization of the
chromatin within the intact nucleus; namely their number, DNA packing ratio and fiber diameter. A systematic comparison among
all the numerous models, being so far proposed for the quinternary and quaternary levels of DNA folding, to identifies the
rope or ribbon-like and the chromonema as the ones that best fit with the in situ distribution.
This revised version was published online in June 2006 with corrections to the Cover Date. |
