PROGRAMMED CELL-DEATH IN DICTYOSTELIUM

Programmed cell death (PCD) of Dictyostelium discoideum cells was trig gered precisely and studied quantitatively in an in vitro system invol ving differentiation without morphogenesis. In temporal succession aft er the triggering of differentiation, PCD included first an irreversib le step leading to the inability to regrow at 8 hours. At 12 hours, ma ssive vacuolisation was best evidenced by confocal microscopy, and pro minent cytoplasmic condensation and focal chromatin condensation could be observed by electron microscopy. Membrane permeabilization occurre d only very late (at 40-60 hours) as judged by propidium iodide staini ng. No early DNA fragmentation could be detected by standard or pulsed field gel electrophoresis. These traits exhibit some similarity to th ose of previously described non-apoptotic and apoptotic PCD, suggestin g the hypothesis of a single core molecular mechanism of PCD emerging in evolution before the postulated multiple emergences of multicellula rity. A single core mechanism would underly phenotypic, variations of PCD resulting in various cells from differences in enzymatic equipment and mechanical constraints. A prediction is that some of the molecule s involved in the core PCD mechanism of even phylogenetically very dis tant organisms, e.g. Dictyostelium and vertebrates, should he related.