Related Experiment Videos
Coordinated induction of the ubiquitin conjugation pathway accompanies the developmentally programmed death of insect
A L Haas1, O Baboshina, B Williams
1Department of Biochemistry, Medical College of Wisconsin, Milwaukee 53226, USA.
Abstract:
The developmentally programmed cell death of abdominal intersegmental muscles in the tobacco hawk-moth Manduca sexta is coincident with a 10-fold induction of the polyubiquitin gene as a hormonally regulated event (Schwartz, L. M., Myer, A., Kosz, L., Engelstein, M., and Maier, C. (1990) Neuron 5, 411-419). Solid phase immunochemical assays measuring intersegmental muscle pools of free and conjugated ubiquitin reveal that the induction of polyubiquitin mRNA is accompanied by a proportional increase in total ubiquitin polypeptide. Ubiquitin conjugate pools increase 10-fold at eclosion, during which loss of muscle protein mass is maximum. A smaller but measurable increase in ubiquitin conjugates is observed earlier in pupal development coincident with a modest enhanced degradation of myofibrillar proteins. Accumulation of ubiquitin conjugates is accompanied by induction in the pathway for polypeptide ligation, including the activating enzyme (E1), several carrier protein (E2) isoforms, and ubiquitin:protein isopeptide ligase (E3). Both accumulation of ubiquitin polypeptide and the enzymes of the conjugation pathway are subject to regulation by declining titers of the insect molting hormone 20-hydroxyecdysone, which signals onset of programmed cell death in the intersegmental muscles. Thus, programmed cell death within the intersegmental muscles is accomplished in part by stimulation of the ubiquitin-mediated degradative pathway through a coordinated induction of ubiquitin and the enzymes responsible for its conjugation to yield proteolytic intermediates. This suggests enzymes required for ubiquitin conjugation may represent additional genes recruited for developmentally programmed death.
Insights
Programmed cell death in Manduca sexta muscles involves a 10-fold increase in ubiquitin, a protein essential for degradation. This process is regulated by the insect molting hormone 20-hydroxyecdysone.
Area of Science:
- Developmental Biology
- Molecular Biology
- Cell Death Research
Background:
- The tobacco hawk-moth Manduca sexta undergoes developmentally programmed cell death of abdominal intersegmental muscles.
- This process is hormonally regulated and involves significant changes in gene expression and protein degradation.
Purpose of the Study:
- To investigate the role of the ubiquitin-mediated protein degradation pathway in the programmed cell death of Manduca sexta intersegmental muscles.
- To determine the hormonal regulation of ubiquitin and its conjugation enzymes during this developmental event.
Main Methods:
- Solid phase immunochemical assays were used to measure ubiquitin pools (free and conjugated) in intersegmental muscles.
- Polyubiquitin mRNA levels and the expression of ubiquitin conjugation enzymes (E1, E2, E3) were assessed.
Main Results:
- A 10-fold induction of polyubiquitin mRNA and a proportional increase in total ubiquitin polypeptide were observed.
- Ubiquitin conjugate pools increased 10-fold at eclosion, coinciding with maximum muscle protein loss.
- The enzymes involved in ubiquitin conjugation (E1, E2, E3) also showed increased expression.
- Both ubiquitin accumulation and conjugation enzyme induction were linked to declining levels of 20-hydroxyecdysone.
Conclusions:
- Programmed cell death in Manduca sexta intersegmental muscles is partly mediated by the ubiquitin-degradative pathway.
- This pathway is activated through coordinated induction of ubiquitin and its conjugation enzymes.
- Enzymes for ubiquitin conjugation may be recruited genes for developmentally programmed cell death.