Fig. 4: MSG and morphological variability.

a, Illustration of the concept of mean shape for staging group 8 (i) and workflow for obtaining a mean shape and local variability estimation for each staging group (ii). In ii, the left shows the process of surface map computation. The blue shape represents the mesh of the reference specimen of the group. The arrows represent the surface mapping from the reference specimen mesh to all others in the staging group. The right shows the working principle of the surface map computation. The landmarks (lm) identify corresponding locations in the reference and target mesh. Shapes of the group after rigid registration to the reference mesh are also shown (iii). Every vertex in the reference mesh (blue dot) has a corresponding point on the other shapes (red dots). b, Calculated myocardium mean shapes for every staging group. The two top rows show the mean shapes from ventral (left) and dorsal (right) views. The two bottom rows show the same mean shapes color coded according to the morphological variability calculated for each vertex. The shape in gray indicates that the low number of specimens at this stage precludes variability calculation. The yellow dotted line and arrows represent the cut trajectory to achieve genus 0 topology in dorsally closed hearts (Methods). Arrowheads indicate the regions of higher variability in medial ventricular regions (solid) and lateral ventricular regions (open). c, Representative specimens of each group. Top, ventral and dorsal view of the myocardium shape. Bottom, ventral and dorsal views of the pericardial tissues of the representative embryos.