Fig. 3.

Notch1a/Emx2 asymmetry is dispensable for cell-pair rotations. (A) Illustration of the cell-cell interfaces, shapes of which are classified as curved (C), linear (I), S or Ƨ shaped. Because an Ƨ cannot be rotated into an S, a distinction is made of the rotation direction. (B) The frequency of distinct interface shapes during inversion. The most common shape is a straight interface (63.41%), followed by curved (21.31%) and then S-shaped curves (S: 6.57% and Ƨ: 8.7%). No shape consistently correlated with the chirality of rotation. (C) Scheme of the topological interactions between all epithelial cells during the inversion of a cell pair (representing one empirical example). Each circle is an individual cell. The area of each circle is proportional to the area of real cells from microscopy images. Straight lines (edges) represent a physical contact between any two cells. Cells are considered neighbors if there is an edge connecting them. A pair of hair cells is colored blue and orange. Neighboring cells are colored light blue if they connect only to the blue sibling in a given frame; yellow if they only connect to the other sibling; or green if they are connected to both. (D) Absolute cumulative difference in the number of neighbors for each cell of inverting (blue) and non-inverting (red) pairs. The difference of neighbors at a given time is the number of neighbors of Cell A minus the number of neighbors of Cell B. The cumulative difference at any given time T is the sum of the neighbor differences from time 1 to time N. Therefore, if there is no cell with a constantly higher number of neighbors over time, the cumulative difference remains close to zero. However, if either one of the cells constantly has more neighbors, over time the absolute cumulative difference will go up. Vertical dashed line and gray shaded areas mark the median and standard deviation of the Phase 2I for the inverting cells in this sample. Shown is the LOESS smoothing of inverting and non-inverting trajectories. (E) Fraction of hair-cell pairs that invert in wild type, emx2 mutant and notch1a mutant larvae. n (number of cell pairs)=71 from wild type, 42 from emx2 mutant, 22 from notch1a mutant larvae.