Drosophila jump muscle myofibrils: A new tool for investigating activation and relaxation

Figures

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  Figure 1. The structure of the S-1 region of the Drosophila IFM myosin. All Drosophila muscle myosin isoforms are produced from a single myosin heavy chain gene (Mhc) via alternative mRNA splicing. The colored alternative exon encoded regions are labeled with the jump muscle version/EMB version. PDB ID: 8EXW. DOI Citation: Caldwell, J.T., Huxford, T., Bernstein, S.I., Stec, B., (2022) Drosophila melanogaster indirect flight muscle myosin II (subfragment-1), doi: https://doi.org/10.2210/pdb8exw/pdb.

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  Figure 2. Drosophila myofibril isolation. (A) Tergal depressor of the trochanter (TDT, aka jump muscle) fibers were dissected from the thoraces of 2- to 3-day-old female Drosophila and chemically permeabilized using Triton X-100. Red lines indicate locations of cuts. (B) An isolated TDT prior to sonication. (C) A single TDT myofibril mounted between a static post (left) and the cantilever force transducer (right).

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  Figure 3. Myofibril tension production. (A) Representative myofibril tension traces were aligned using the digital trigger signals, and resting tension has been subtracted. (B) Maximum active tension is higher for EMB compared with control and w1118 myofibrils. The central line of the violin plot is the mean of the data shown (one-way ANOVA followed by Tukey’s multiple comparisons, n = 27–31 myofibrils per group, p-values shown above brackets).

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  Figure 4. Myofibril activation. (A) The averaged activation phase of the myofibrils normalized to their maximum tension. (B) EMB activation rate is significantly slower than the other two lines. The central line of the violin plot is the mean of the data shown (one-way ANOVA, n = 27–31 myofibrils per group. p-values shown above brackets).

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  Figure 5. Myofibril relaxation. (A) The averaged relaxation phase of the myofibrils normalized to their maximum tension. The small arrow indicates where solution was changed from pCa 4 (activating) to pCa 8 (relaxing). The time between this point and the start of the exponential tension drop is the linear phase of relaxation, and the dotted line indicates the rate of linear relaxation. (B–D) Quantification of relaxation properties. The central line of the violin plot is the mean of the data shown (one-way ANOVA, followed by Tukey’s multiple comparisons, n = 27–31 myofibrils per group. p-values are shown above brackets).

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  Figure 6. Sonication compared with mechanical homogenization. Mouse cardiac myofibril mechanics and kinetics following either mechanical homogenization (10 s ×2, 17,000 rpm) or sonication. The central line of the violin plot is the mean of the data shown. Data were compared using an unpaired Student’s t test, n = 9 myofibrils per group. p-values are shown above brackets.