Figure 5. M308 determines circadian rhythms and heart tube physiology in Drosophila melanogaster.

(A) Representative actograms of WT and CaMKII^M308V flies. Actograms are double plotted with yellow bars representing light exposure. (B) CaMKII^M308V flies have a significantly longer free-running circadian period, as estimated by χ² periodogram (WT n = 99, CaMKII^M308V n = 120). Bars denote mean ± SEM. (C) CaMKII^M308V flies exhibit significantly decreased average daily locomotion during constant darkness, as measured by beam-break counts per day (WT n = 99, CaMKII^M308V n = 120). Bars denote mean ± SEM. (D) Circadian χ² amplitude indicates increased rhythm strength of CaMKII^M308V flies under constant darkness (WT n = 99, CaMKII^M308V n = 120). Bars denote mean ± SEM. (E) Representative M-mode kymograms generated from high-speed videos of beating WT and CaMKII^M308V fly heart tubes. Top panel shows cardiac cycle dynamics and heart wall contraction over time. Bottom panel shows individual systolic intervals of WT and CaMKII^M308V flies. CaMKII^M308V flies exhibit reduced wall movement distance (d) during systole and a prolonged time of shortening (t_s) resulting in significantly diminished shortening speed. (F–I) CaMKII^M308V flies have markedly impaired heart function compared with WT flies. CaMKII^M308V flies at baseline exhibit (F) decreased cardiac output, (G) decreased fractional shortening, (H) decreased shortening speed, and (I) decreased relaxation rate (WT n = 33, CaMKII^M308V n = 30). (J) CaMKII^M308V heart tube diastolic diameter is markedly increased after intracellular Ca²⁺ chelation with EGTA-AM compared with WT heart tubes (WT n = 20, CaMKII^M308V n = 23). *P < 0.05, **P < 0.01, ***P < 0.001 by 2-tailed Student’s t test (B–D and F–I) or 2-tailed Mann-Whitney test (J).