Programmed cell death (PCD) is an essential component of animal development and serves a variety of functions. The intersegmental muscles (ISMs) of the tobacco hawkmoth Manduco sexta provide a useful model system to study the molecular mechanisms that mediate PCD. The ISMs participate in the emergence behavior of the adult moth at the end of metamorphosis and then die during the subsequent 30 hours. In addition, several populations of interneurons and uniquely identified motor neurons also die following adult emergence. The trigger for this death is a decline in the circulating titer of the molting hormone 20-hydroxyecdysone. Previous work has demonstrated that the ability of the ISMs to die is dependent on new gene expression. Using a differential hybridization cloning strategy, a cDNA library generated from condemned ISMs was screened, and four up-regulated clones were isolated. One of these recombinants was found to encode apolipophorin III (apoLp-III), a component of lipophorin. The expression of apoLp-III was dramatically elevated with the death of the ISMs, some interneurons and identified motor neurons. ApoLp-III was not detectably associated with apolipophorin I and II, required components of lipophorin, or with other molecules in the dying cells, suggesting that apoLp-III has activities independent of lipid transport that may play a role in programmed cell death. Another clone, 18-56, encodes a phylogenetically conserved ATPase domain-containing (CAD) family member related to putative proteasomal subunits and transcriptional regulators. While clone 18-56 was expressed in all tissues examined and during every stage of ISM development, there was a dramatic increase in its expression at both mRNA and protein levels when the ISMs became committed to die. Furthermore, the mouse homolog of 18-56, m56, was cloned and its expression pattern was examined in the mouse. No correlation was detected between enhanced m56 expression and apoptosis in mammalian cells, suggesting that the molecular pathway used by the ISM death may be distinct from that of apoptosis. Rat-1 fibroblast cell lines that over or under express m56 were generated, thus providing tools for further functional study of m56 in mammalian cells.
| Identifer | oai:union.ndltd.org:UMASS/oai:scholarworks.umass.edu:dissertations-7636 |
| Date | 01 January 1996 |
| Creators | Sun, Danhui |
| 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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