Extended Fig. 9: H3K9 trimethylated chromatin occupancy peaks in the direction of contraction in nuclei with tensile loading mode.

Embryonic CMs were cultured on soft (13 kPa) PDMS for two days after which image stacks of CM nuclei were recorded during contractions to determine the direction of nuclear translation. Cells were then stained for chromatin markers H3K9me3, H3K27me3 or actively transcribed chromatin (RPIIS2). Chromatin marker occupancy was calculated with respect to the angle of the nuclear center with the angle of nuclear translation set to 0°. Cells with extended major axis during contraction (tensile loading mode, n=20, same as intranuclear analysis) showed a distinct peak of H3K9me3 intensity ±30° around the direction of translation while a decline in H3K9me3 intensity was observed for cells with shortened major axis (compressive loading mode, n=8). Right side provides a graphic illustration of angular analysis showing nuclear outlines during resting phase (doted black) and peak contraction (solid green). The black arrow indicates the direction of translation, which defines the 0° point, and green arrows demonstrate extension or compression of the nuclear major axis used to determine the loading mode of cells; areas=SEM; from 5 exp.