Analysis of cell movements with respect to the long and short axis.

A: Scheme showing how cell positions were projected on the long axis of the gastruloid. An ellipse was fitted to the outline of the gastruloid. The angle θ between the long axis of the ellipse and the nearest orthogonal axis when rotating counter-clockwise was determined for each time point (top panel). Positions of cells were rotated by the angle θ to project them on the long axis of the gastruloid. Here, the new x coordinate of each cell corresponds to the cell’s position on the long axis, and the new y coordinate to the cell’s position on the short axis. For each cell, the movement along the long axis vl (xend − xstart) or along the short axis vs (yend − ystart) was determined, and normalized by the length of the long axis L or the short axis S, respectively. The resulting vl/L was plotted against the end position of each cell projected on the long axis (mid panel). The resulting vs/S was plotted against the end position of each cell projected on the short axis (bottom panel). B: Distance each cell has moved along the short axis plotted against the end position of each cell projected on the short axis. Large, pink circles represent measured cells. Small, black circles represent cells in the simulated gastruloid. C, top panel: Same plot as in B with data points colored by the direction of movement with respect to the short axis. Orange: cells are moving inwards, towards the long axis; dark blue: cells are moving outwards, away from the long axis; light blue: cells that cross the long axis, thus first move inwards, then outwards. Bottom panel: distance each cell has moved along the short axis plotted against the end position of each cell projected on the long axis. Cells are colored in the same way as in the top panel. Large circles represent measured cells. Small circles represent cells in the simulated gastruloid. (EPS)