Nucleolar segregation during apoptosis of haemopoietic stem cell line FDCP-Mix

The programmed elimination of cells during apoptosis is distinct from necro sis both morphologically and biochemically, Currently, the morphological de scription of apoptosis discriminates between the segregation of the nucleol us and the so called 'chromatin condensation', The latter originates from o bservations of electron dense material adjacent to the nuclear envelope of apoptotic nuclei, Although there is ample evidence for an involvement of DN A in electron dense marginations, their true nature is still unknown. By st udying apoptosis in FDCP-Mix, a pluripotent murine haemopoietic stem cell l ine, we found morphological and histochemical evidence that electron dense material at the nuclear envelope (NE) has emerged as a result of the segreg ation of nucleoli in association with the nuclear membrane. The remaining e lectron dense and homogenous bulk of the nucleolus labels for RNAse-gold, b ut even more intensely for DNAse-gold, and therefore could possibly be mist aken as 'condensed chromatin' in the light microscope. The labelling of the electron dense material for DNase gold in FDCP-Mix could be explained by a migration of DNA into the bulk of the nucleoli at an early stage of cell d eath.