PROGRAMMED CELL-DEATH - EARLY CHANGES IN METAMORPHOSING CELLS

Programmed cell death in intersegmental muscles and labial glands of M anduca sexta is a type II form of active cell death, in which lysosoma l destruction of cytoplasm is a prominent and early feature, and the c ollapse of the nucleus is late and relatively modest until the bulk of the cytoplasm has been eroded. The prominent features of this collaps e include an early expansion of the lysosomal compartment and a decrea se in overall protein synthesis, while a small number of mRNAs persist or are upregulated. Energy resources appear to be adequate during the early stages of degeneration, and changes in levels of second message s likewise do not seem to be sufficiently dramatic to explain the fail ure of the tissue. There is some suggestion that DNA may not be comple tely intact long before the labial gland finally collapses, suggesting that it may fail under heavy load. Otherwise, we do not yet have an e xplanation for the precipitous drop in overall protein synthesis.