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Insect muscle as a model for programmed cell death
1Department of Biology, Morrill Science Center, University of Massachusetts, Amherst 01003.
Abstract:
Programmed cell death (PCD) is a fundamental component of development in virtually all animals. Despite the ubiquity of this phenomenon, little is known about what tells a cell to die, and less still about the physiological and molecular mechanisms that bring about death. One system that has proven to be very amenable for the study of PCD is the intersegmental muscle (ISM) of the tobacco hawkmoth Manduca sexta. These giant muscle cells are used during the eclosion (emergence) behavior of the adult moth, and then die during the subsequent 30 h. This review uses the ISMs as a model system to address questions that are basic to any cell death system, including the following: (1) how do cells know when to die; (2) what physiological changes accompany death; (3) what are the molecular mechanisms that mediate death; and (4) do all cells die by the same process? For the ISMs, the trigger for PCD is a decline in the circulating titer of the insect molting hormone, 20-hydroxyecdysone (20-HE). During cell death there are rapid decreases in both the myofibrillar sensitivity to intracellular calcium and the resulting force of fiber contraction. The ability of the ISMs to undergo PCD requires the repression and activation of specific genes. Two of the repressed genes encode actin and myosin. One of the upregulated presumptive cell-death genes encodes polyubiquitin, which appears to play a critical role in the rapid proteolysis that accompanies ISM death.(ABSTRACT TRUNCATED AT 250 WORDS)
Insights
Programmed cell death (PCD) in animals is triggered by hormonal decline, as seen in Manduca sexta intersegmental muscles. This process involves gene regulation and physiological changes leading to cell death.
Area of Science:
- Developmental Biology
- Cell Biology
- Insect Physiology
Background:
- Programmed cell death (PCD) is crucial for animal development, yet triggers and mechanisms remain unclear.
- The intersegmental muscles (ISMs) of Manduca sexta offer a tractable model for studying PCD.
- ISMs undergo PCD post-eclosion over 30 hours.
Purpose of the Study:
- To investigate the triggers, physiological changes, and molecular mechanisms of PCD using ISMs.
- To determine how cells recognize the signal to die.
- To explore whether PCD mechanisms are conserved across different cell types.
Main Methods:
- Utilizing the Manduca sexta ISM system as a model for PCD research.
- Analyzing physiological changes during ISM cell death.
- Investigating gene expression patterns (repression and activation) during PCD.
Main Results:
- PCD in ISMs is triggered by a decrease in the insect molting hormone 20-hydroxyecdysone (20-HE).
- Cell death involves reduced myofibrillar sensitivity to calcium and decreased contraction force.
- Gene regulation is essential for PCD, with actin and myosin repressed, and polyubiquitin upregulated.
Conclusions:
- The decline of 20-HE acts as a critical trigger for ISM PCD.
- PCD involves significant physiological alterations and specific gene expression changes.
- Polyubiquitin plays a key role in the proteolysis observed during ISM death, highlighting molecular mechanisms of cell demise.