NUCLEAR-PORE CLUSTERING IS A CONSISTENT FEATURE OF APOPTOSIS IN-VITRO

Two cell lines which show different patterns of DNA fragmentation have been examined for variations of their nuclear morphology during apopt osis. FDCP-Mix, a pluripotent murine haemopoietic stem cell line which undergoes typical internucleosomal cleavage of DNA when induced to ap optosis either by drugs or withdrawal of growth factor (IL-3) was comp ared with the human lymphoid leukemia cell line MOLT-4, a cell line wh ich undergoes apoptosis without production of a typical DNA 'ladder'. The nuclear morphology of FDCP-Mix cells was consistent after apoptoti c induction by drug or by growth factor withdrawal. Apoptotic nuclear morphology for MOLT-4 and FDCP-Mix showed variations in the distributi on, density and texture of the electron dense nuclear marginations. De spite these differences, clustering of nuclear pore complexes (NPCs) a fter treatment with the topoisomerase II inhibitor etoposide was a com mon phenomenon for both cell lines. Moreover, pore clustering for FDCP -Mix nuclei occurred independently from the way in which apoptosis was induced, either by growth factor withdrawal or etoposide treatment. I n a novel approach, we visualised the clustering of NPCs three-dimensi onally by field emission in-lens scanning electron microscopy (FEISEM) .