JEB desktop wallpaper calendar 2016

JEB desktop wallpaper calendar 2016

Alternative splicing, muscle contraction and intraspecific variation: associations between troponin T transcripts, Ca2+ sensitivity and the force and power output of dragonfly flight muscles during oscillatory contraction
James H. Marden, Gail H. Fitzhugh, Mahasweta Girgenrath, Melisande R. Wolf, Stefan Girgenrath
  1. Fig. 1.

    (A) The basalar muscle (BM) of the mesothorax exposed by removal of a portion of the cuticle and underlying air sacs. The viewpoint is looking posteriorly from the rear margin of the head and slightly above the dragonfly; the base of the left forewing is visible near the upper right. White arrows show the lateral edges of the humeral plate, around which incisions were made to isolate the basalar muscle mechanically for studies of contractile performance. (B) Sample trace of wing position and velocity from a recording made using a laser distance sensor on the base of the forewing. (C) Photograph showing a dragonfly attached by its ventral thorax to a narrow glass beam (not visible) that extends from a strain gauge. A fine-gauge thermocouple and EMG electrodes are inserted into the thorax. The laser distance sensor is shown at the upper right. We have drawn a red line to depict the laser beam striking a white spot painted at the base of the right forewing. (D) Diagram showing the geometry of the basalar muscle attachment to the base of the forewing, an approximation of the EMG recording electrodes (these are differential electrodes referenced to a third electrode in the abdomen that is not shown) and the method used to calculate wing position from the laser distance sensor.

  2. Fig. 2.

    (A) Simultaneous recordings from EMG signals and wing position during tethered flight (see Fig. 1C,D). Note the slow time course and variable amplitude of EMG events. The first burst of neural events had a frequency (44 Hz; this is presumably an artifact of tethered flight) that resulted in relatively little wing motion. The second burst is at a lower frequency, which resulted in a higher wingbeat amplitude and an average vertical force that was 1.87 times body weight (measured simultaneously from a strain gauge; that trace is not shown here). (B) Examples of recordings made by Simmons (Simmons, 1977b), which have been reproduced here to match the relative amplitude and time scale of the EMG traces shown in A. Simmons’ data are (i) from intracellular electrodes in a flight muscle motor neuron during low-frequency wing flapping, (ii) from intracellular electrodes in a motor neuron caused to fire by peripheral electrical stimulation at the muscle and (iii) from an extracellular suction electrode attached to a small group of muscle fibers during tethered flight. Both intra- and extracellular recordings show variability in the time course and amplitude of spikes. The time base shown in A applies also to B.

  3. Fig. 3.

    Work loops at a contraction frequency of 37 Hz for a muscle preparation stimulated at seven different points on the strain cycle. Net work output was maximized in the green trace, which was produced by stimulation at 44 % of the lengthening cycle. The phase (percentage of the lengthening cycle) for the other stimulus phase relationships tested are shown.

  4. Fig. 4.

    (A) Work loop from a basalar muscle contracting at 37 Hz and an illustration of the variables measured for work-loop analyses. (B,C) Work loops at various contraction frequencies for two basalar muscles that represent the range of variation in specific work and power output. Force is plotted as a function of changes in muscle length. Arrowheads indicate the direction of progression around the loop. The muscle in B was larger (16.7 mg), yet generated less tension and power (maximum power at any frequency was 66 W kg–1) than the muscle in C (14.8 mg; 156 W kg–1). Both series were obtained at a tissue temperature of 32°C and a constant phase between electrical stimulation and muscle lengthening. Net work is as follows: B, 0.9 J kg–1 for 20 Hz, 2.1 J kg–1 for 30 Hz and 1.3 J kg–1 for 40 Hz; C, 3.7 J kg–1 for 20 Hz, 5.0 J kg–1 for 20 Hz and 2.3 J kg–1 for 20 Hz.

  5. Fig. 5.

    Examples of the Ca2+ concentration/tension relationship measured from different skinned muscle fiber preparations. Tension is expressed as a percentage of maximum tension. (A) Muscle fibers with different Ca2+ sensitivity (pCa50) and similar Hill coefficients (nH). (B) Muscle fibers with similar Ca2+ sensitivity but different Hill coefficients.

  6. Fig. 6.

    Ca2+ sensitivity (pCa50) as a function of the sum of the relative abundance of two troponin transcripts, troponin T (TnT) 261 and TnT 267 (see Table 1). Open symbols represent individuals from Ten Acre Pond and filled symbols represent individuals from Mothersbaugh Pond. Circles represent the early-emerging morph; squares represent the late-emerging morph. The point at the far left side of the plot was excluded from the statistical analysis and the curve fit because it does not conform to either linear or curvilinear models. It does, however, support the association between low levels of particular TnT transcripts and low Ca2+ sensitivity.

  7. Fig. 7.

    Ca2+ sensitivity (pCa50) as a function of relative maturity, measured as residuals of the regression of the cube root of body mass on forewing length. (A) Data representing the early-emerging morph. (B) Data representing the late-emerging morph. In both panels, open symbols represent individuals from Ten Acre Pond; filled symbols represent individuals from Mothersbaugh Pond.

  8. Fig. 8.

    Specific work (J kg–1) during work-loop contractions at 37 Hz in relation to the relative abundance of troponin T (TnT) 267. Symbols are as in Fig. 6.

  9. Fig. 9.

    Onset of active tension (shown as a percentage of the total length cycle, where 50 % is the transition from lengthening to shortening; onset was judged by comparing passive with active loops for each muscle) during contraction at 37 Hz in relation to Ca2+ sensitivity (pCa50).

  10. Fig. 10.

    Peak force produced during contraction cycles at 37 Hz in relation to the sum of the relative abundance of troponin T (TnT) transcripts 261 and 267. Symbols are as in Fig. 6. The point at the far left of the plot was excluded from the statistical analysis and the curve fit because it does not conform to either linear or curvilinear models. It does, however, support the association between low levels of particular TnT transcripts and force output.

  11. Fig. 11.

    Force halfway through the shortening cycle during contractions at 37 Hz in relation to the relative abundance of troponin T (TnT) transcript 267. Symbols are as in Fig. 6.

  12. Fig. 12.

    Representative traces of specific power output over integer contraction frequencies between 20 and 45 Hz for five basalar muscle preparations.

  13. Fig. 13.

    (A) Maximum power output at any contraction frequency in relation to the relative abundance of troponin T (TnT) transcripts 261 and 267. (B) Maximum power output at any contraction frequency in relation to Ca2+ sensitivity (pCa50). Symbols are as in Fig. 6.

  14. Fig. 14.

    cDNA sequence of the 5′ ends of a sample of troponin T (TnT) transcripts that do not contain alternative exon 5. cDNA was amplified from three individuals from Ten Acre Pond (TenA.148, TenA.133 and TenA.156) and two from Mothersbaugh Pond (MbB.11 and Mb.16) using primers against the 5′ untranslated region and constitutive exon 8. Products from polymerase chain reactions were subcloned and sequenced. The bar at the top of the plot shows the exon structure, below which is the consensus sequence. Only the coding region through a portion of exon 7 is shown here.