Figure 2. Ratcheting of contractile pulses correlates with persistent myosin structures.

(a) Unconstricting pulses are enriched in low-amplitude myosin pulses. Distributions of pulse amplitude-bin for each pulse behaviour class are shown. (b) Schematic for the myosin persistence measurement. Myosin persistence is defined as the difference between the before-peak and after-peak myosin intensity minima (ΔI) normalized by the average intensity (I_mean) during the pulse. (c) Ratcheted pulses display more persistent myosin after the pulse measured for wild-type cells. Myosin persistence measured for wild-type ratcheted and unratcheted pulses reveal the lack of persistent myosin intensity in unratcheted pulses (P<10⁻⁷, unpaired t-test). Red bars represent sample medians and boxes demarcate the 25th and 75th percentiles. (d,e) Myosin persistence is associated with pulse-ratcheting. The degree of membership in the ratcheted class (d) correlates with myosin persistence (R=0.101, P>0.05), while the degree of membership in the unratcheted class (e) significantly anticorrelates with myosin persistence (R=−0.301, P<10⁻⁴). Lines represent best-fit lines. (f,g) Representative images of a ratcheted pulse (f, arrowhead) show persistent myosin structures (f, arrow), while an unratcheted pulse (g, arrowhead) does not. Scale bars, 5 μm.