Programmed cell death of the prothoracic glands of Manduca sexta during pupal-adult metamorphosis.

The degeneration of the prothoracic glands of Manduca sexta during pupal-adult metamorphosis was analyzed by both light and transmission electron microscopy, and correlated with a functional analysis of the ability of the prothoracic glands to synthesize ecdysteroids in vitro. Apoptosis of degenerating glandular cells was also examined by in situ indirect immunofluorescein detection of digoxigenin-labeled genomic DNA cleavage (the TUNEL method). The ability of the prothoracic gland to synthesize ecdysteroids reached a peak 4 days after pupation, decreased drastically on day 6 and then decreased further to the basal level 2 days later. Prothoracic gland degeneration was initiated on day 6 and was characterized by nuclear condensation, cytoplasmic budding, giant autophagic vacuoles, the disappearance of the smooth endoplasmic reticulum and intercellular channels, and the fragmentation of the cytoplasm into membrane-bound bodies. The cell debris of these degenerating cells was then engulfed by numerous phagocytic hemocytes. The results of the analysis of apoptosis by immunofluorescence detection are in complete accord with the histological, ultrastructural and radioimmunoassay data, suggesting that apoptosis is the basic mechanism for programmed cell death of the cells comprising these vital glands.