Figure 1.

Overview of the anisotropic subcellular element method. (a) Schematic of the stratified epidermis comprised of a single layer of basal cells and multiple layers of suprabasal cells. The highlighted basal cells depict the division planes for (a) symmetric division. (b) Scaled plot of the intercellular and intracellular forces acting on an element versus element separation. The intracellular force cut-off line is the separation at which we assume cell–cell adhesion no longer operates, so the force between elements in different cells is set to zero. (c) An illustration of the implementation of cell division. Part (i) shows a cell that is ready to divide, (ii) shows the same cell after it has distributed its elements to two daughter cells, but before any cell motion has occurred and (iii) shows the cell after the change from intracellular forces to intercellular forces has pushed the two daughter cells apart. (d) Schematic of forces. The arrows represent the forces acting on the pairs of element types with thicker arrows representing stronger forces. These forces are strongly repulsive at short range and attractive at longer ranges as shown in (c). The dark blue elements are the basal elements of the basal cells and adhere to the basement membrane by way of an external attractive force. The light blue elements are the apical elements of the basal cells and have a very weak repulsion from the basement membrane (not shown). The red elements are the elements destined to be part of suprabasal cells that do not interact with the membrane. When modelling cells with strong polarity the red arrow in (a) only provides a short-range repulsive force and no attractive force. Forces between pairs of element types not shown are strictly repulsive, preventing elements from overlapping. (e) Two cells with an identical number of elements (36) but comprised of one or two element types. The left cell is comprised of only a single element type to a round or cuboidal shape. The right is made up of two distinct element types (e.g. apical and basal). Their interaction rules lead to segregation and the resulting columnar shape.