Figure 1.

Metrics of Contractile Architecture to Characterize the Progression of Myofibrillogenesis

(A) Schematic representation of a sarcomere (i) and of the distribution of α-actinin (red) during myofibrillogenesis: in the cytoplasm (ii), along the actin (green) filament in the form of Z-bodies (iii), and incorporated into the Z-disks (iv).

(B) Algorithmic detection of the orientation and periodic registration of α-actinin-positive structures using the image spatial (coordinates x,y) and Fourier (coordinates u,v) domains.

(C) Color-coded orientations (i, from the inset of synthetic image Figure 1Bii) displayed into a histogram (ii) can be fitted to identify orientations belonging to Z-disks (red) and Z-bodies (black). In parallel, the 2D Fourier power spectrum (iii) was integrated into a 1D curve (iv) and fitted to identify the contribution of periodically spaced Z-disks (red) and aperiodic Z-bodies (black).

(D) α-actinin immunostains (white) of mononucleated (DAPI, blue) murine primary (mpCM, i) and murine (miCM, ii) or human (hiCM, iii) induced pluripotent stem cell-derived cardiomyocytes. The color-coded representation of the α-actinin orientation in the inset is reported below the image. The positive semiplane for the Fourier transform is reported on the right of each image.

Scale bar represent 20 μm. See also Figures S2 and S3.