Figure 3.

Schematic diagram of junctional rearrangements, cell division, and cell removal in vertex models. (a) A T1 transition, in which two vertices sharing a short edge merge into a single vertex, which then decomposes into two new vertices such that the local network topology is changed. (b) A T2 transition, in which a cell shrinks to zero area and is removed, corresponding to delamination and/or apoptosis. (c) Example of a T3 transition, in a vertex/edge intersection is avoided by replacing the approaching vertex with two new vertices that are associated with the element. (d) Cell division, in which a parent cell is divided (in this case through its short axis) through the addition of two new vertices, resulting in two daughter cells. (e) Formation and resolution of multicellular rosettes, a generalization of T1 transitions involving a larger number of cells. (a–e) Edges or vertices that are removed (red); edges or vertices that are created (green).