Correlation between Barr body and overall chromatin decondensation in vitro.

Geometric and densitometric properties of the Barr body of early and late phase II confluent human fibroblasts are analysed by the automated image analyser Quantimet 720 D. In cells with the same 2C DNA content, the state of condensation of the Barr body varies proportionally wih the state of condensation of the entire nucleus yielding a correlation between nuclear and Barr body area. In light of these results, indicating the participation of the Barr body in the overall process of chromatin condensation and decondensation, a definitive "'static" separation between dense ("heterochromatic") and dispersed ("euchromatic") regions of chromatin seems to be arbitrary. The implications of these results in terms of a possible attachment of interphase chromatin to the nuclear envelope are briefly discussed.