20-hydroxyecdysone-induced differentiation and apoptosis in the Drosophilacell line, l(2)mbn

20-Hydroxyecdysone has an inhibitory effect on the proliferation of l(2)mbn cells, causes vacuolization and fragmentation of cells, and promotes a str ong phagocytotic activity. From several lines of evidence, it can be conclu ded that 20-hydroxyecdysone induces apoptosis. Long-term video observations following the fate of individual cells, scanning and transmission electron microscopy reveal the typical characteristics of apoptosis: sequestration of small cellular protuberances or larger parts of the cell with nuclear fr agments (apoptotic bodies), chromatin condensation, condensation and vesicu lation of cytoplasm, whereas the mitochondria retain their normal appearanc e, The induction of apoptosis by 20-hydroxyecdysone was confirmed by the TU NEL reaction and quantitatively determined by a method based on this reacti on. Onset of apoptosis precedes phagocytotic activity. JH III alone has no clear-cut effect on l(2)mbn cells. In double treatments, the inhibitory eff ect of 20-hydroxyecdysone on cell proliferation is significantly reduced by the addition of JH III. Whether or not JH III also reduces apoptotic activ ity is not yet clear. It is shown that the l(2)mbn cell line is an advantag eous model system for the exploration of steroid-induced apoptosis. (C) 200 0 Harcourt Publishers Ltd.