Fig. 8.

A model of cell-pair rotation in vivo. Overview of cell-pair inversion process summarizing the key elements of the inversions in wild type on the left, and stating major differences occurring in the notch1a^−/− and emx2^−/− larvae on the right. The precision of the angular movement in vivo approaches that of cells in vitro. Phase 1 starts immediately after division of the UHCP, is characterized by a coordinated shape of the cells and expansion of the homotypic bond. Phase 2 marks the maximum of circularity of the dyad, the length of the homotypic bond and of angular velocity. Mutant rotations are characterized by significant wobbling, denoted by double-headed arrows. A computational model recapitulates this dynamic difference just by assuming that the minima of energy potentials are either symmetric or asymmetric (green and blue curves represent the Gaussian wells to which minima the respective cells are attracted in our computational model). In Phase 3 the angle between the cells and the A-P axis (blue lines) is 0 with high accuracy and precision but it is misaligned in mutants. The symmetric and asymmetric models can also explain these differences.