Programmed cell death (PCD) is an essential developmental process in all multicellular organisms. It serves multiple functions including selected removal of unneeded and/or deleterious cells, and regulation of cell numbers (reviewed in Milligan and Schwartz, 1996). The intersegmental muscles (ISMs) of the hawkmoth Manduca sexta provide an ideal model for studying PCD (reviewed in Schwartz, 1992). In response to a decline in the circulating titer of the steroid hormone 20-hydroxyecdysone (20-HE), these cells initiate a death program which includes both the up- and down-regulation of specific genes. Following eclosion, the ISMs undergo PCD that results in the complete destruction of the muscles during the subsequent 30 hours (Finlayson, 1956). This dissertation examines in detail the repression of actin and myosin heavy chain expression that occurs when the muscles become committed to die. At the protein level, actin expression was reduced by 84% at the time the muscles were committed to die, which presumably plays a role in the rapid dissolution of the muscles. When the ISMs became committed to die, there were dramatic increases in proteolytic activity that are correlated with an approximately eightfold increase in the absolute amounts of multicatalytic proteinase (MCP). At the time of commitment, four new MCP subunits were observed to be associated with the complex. Correlated with the addition of these new subunits was a dramatic increase in the levels of immunodetectable MCP throughout the cytoplasm and within the nuclei of dying muscles. These changes in MCP were regulated by the same hormonal signals that mediate cell death. Cells dying by PCD often display a characteristic set of features termed apoptosis. These features include chromatin condensation, DNA fragmentation, membrane blebbing and phagocytic removal of the dying cells. However, dying ISMs display few characteristics of apoptosis. Interestingly, apoptotic cell death does occur in Manduca embryogenesis. Evidently Manduca possesses the necessary biochemical machinery to undergo apoptosis and does so in specific developmental circumstances. These data suggest that more than one cell death mechanism is used during development.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7551 |
| Date | 01 January 1996 |
| Creators | Jones, Margaret Elizabeth |
| Publisher | ScholarWorks@UMass Amherst |
| Source Sets | University of Massachusetts, Amherst |
| Language | English |
| Detected Language | English |
| Type | text |
| Source | Doctoral Dissertations Available from Proquest |
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