THE CONDENSATION OF CHROMATIN IN APOPTOTIC THYMOCYTES SHOWS A SPECIFIC STRUCTURAL-CHANGE

Chromatin condensation and DNA cleavage at internucleosomal sites have been recognized early as hallmarks of apoptosis, and it has been sugg ested that extensive DNA chain scission could directly result in the f ormation of dense chromatin bodies, Here we have shown that no causal relationship exists between DNA degradation and chromatin condensation in glucocorticoid-induced thymocyte apoptosis, The chromatin rearrang ement occurred independent of as well as prior to DNA cleavage and inv olved a specific conformational change at the nucleosome level, in the early stages of the process, the core particles appeared to be tightl y packed face-to-face in smooth 11-nm filaments that progressively fol ded to generate a closely woven network, The network finally collapsed , producing dense apoptotic bodies. Since trypsin digestion relaxed co ndensed chromatin and histone H4 underwent appreciable deacetylation i n the apoptotic cell, we suggest that changes in the DNA-histone inter actions represented a major modulating factor of condensation.