The area trend and myosin minima trends are shown in orange.
Amnioserosa cell area measurements can be decomposed into two parts, a long-timescale area trend around which oscillations occur and which decreases over time due to net area contraction, and the oscillatory part (Fig. 1 e).
Apical area strain was defined as cell area relative to a cell area trend computed using a moving window of 6 min. High-frequency noise, residual low-frequency and neighbour effects in both area and rescaled myosin signals were removed via a bandpass filter in the range 1 mHz≤ ν≤12.5 mHz.
Since we are interested in area and myosin dynamics at the timescales of the oscillations, we extracted the oscillatory contribution from individual cell areas by computing the area trend via a moving boxcar average and subtracting this from the raw area measurements.
Normalising the oscillatory contribution by the area trend and applying a bandpass filter to remove high-frequency noise and low-frequency residuals, we obtained an apical cell area strain, which provides a measure of relative cell area deformation (Fig. 1 f).
