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Updated: Jul 31, 2026
Optical Cross-Sectional Muscle Area Determination of Drosophila Melanogaster Adult Indirect Flight Muscles
Published on: March 31, 2018
Paramyosin phosphorylation site disruption affects indirect flight muscle stiffness and power generation in
Hongjun Liu1, Mark S Miller, Douglas M Swank
1Department of Biology and Molecular Biology Institute, San Diego State University, 5500 Campanile Drive, San Diego, CA 92182-4614, USA.
Abstract:
The phosphoprotein paramyosin is a major structural component of invertebrate muscle thick filaments. To investigate the importance of paramyosin phosphorylation, we produced transgenic Drosophila melanogaster in which one, three, or four phosphorylatable serine residues in the N-terminal nonhelical domain were replaced by alanines. Depending on the residues mutated, transgenic lines were either unaffected or severely flight impaired. Flight-impaired strains had decreases in the most acidic paramyosin isoforms, with a corresponding increase in more basic isoforms. Surprisingly, ultrastructure of indirect flight muscle myofibrils was normal, indicating N-terminal phosphorylation is not important for myofibril assembly. However, mechanical studies of active indirect flight muscle fibers revealed that phosphorylation site mutations reduced elastic and viscous moduli by 21-59% and maximum power output by up to 42%. Significant reductions also occurred under relaxed and rigor conditions, indicating that the phosphorylation-dependent changes are independent of strong crossbridge attachment and likely arise from alterations in thick filament backbone properties. Further, normal crossbridge kinetics were observed, demonstrating that myosin motor function is unaffected in the mutants. We conclude that N-terminal phosphorylation of Drosophila paramyosin is essential for optimal force and oscillatory power transduction within the muscle fiber and is key to the high passive stiffness of asynchronous insect flight muscles. Phosphorylation may reinforce interactions between myosin rod domains, enhance thick filament connections to the central M-line of the sarcomere and/or stabilize thick filament interactions with proteins that contribute to fiber stiffness.
Insights
Phosphorylation of paramyosin in Drosophila flight muscles is crucial for generating force and power. Mutations affecting this process impair muscle function without altering myofibril structure.
Area of Science:
- Muscle physiology
- Molecular biology
- Biochemistry
Background:
- Paramyosin is a key structural protein in invertebrate muscle thick filaments.
- Phosphorylation of paramyosin is a potential regulatory mechanism for muscle function.
Purpose of the Study:
- To investigate the role of N-terminal paramyosin phosphorylation in Drosophila melanogaster flight muscle.
- To determine the impact of altered phosphorylation sites on muscle structure, mechanics, and function.
Main Methods:
- Generated transgenic Drosophila melanogaster with mutations in paramyosin phosphorylation sites.
- Assessed flight ability, protein isoform expression, myofibril ultrastructure, and muscle fiber mechanics.
- Performed mechanical studies on active and relaxed muscle fibers.
Main Results:
- Mutations in phosphorylation sites led to flight impairment and altered paramyosin isoform distribution.
- Muscle fiber mechanics were significantly reduced, including elastic and viscous moduli and power output.
- Ultrastructure of myofibrils remained normal, and crossbridge kinetics were unaffected.
- Reduced mechanical properties were observed independent of strong crossbridge attachment.
Conclusions:
- N-terminal paramyosin phosphorylation is essential for optimal force and power transduction in insect flight muscles.
- Phosphorylation influences thick filament properties, contributing to passive stiffness.
- This phosphorylation is critical for the unique mechanical demands of asynchronous insect flight muscles.
