Physical constraints on early blastomere packings
Fig 1
Schematics and definitions of early embryo dynamics.
A, Schematic representation of the most common 4-cell embryo arrangements in the mouse (tetrahedron), C. elegans (diamond) and sea urchin (square). Blastomeres (small spheres) are confined by the surrounding confining envelope (pink; vitelline envelope, hard chitinous egg shell, or hyaline layer, respectively). B, Abstraction of two cells in contact, depicting the cell radius R, equilibrium distance r* and contact angle θ. C, Cell-cell interaction potential Uc(r). D, Examples of cell configurations for varying contact angles. E, Effective volume correction: the overlapping volume (gray, left) is added to each cell by increasing its radius to match the actual cell volume. F, Examples of interaction potentials, Us(r), of a cell with repulsive (left) and sticky (right) confining shells. Repulsive and attractive regions are shown in orange and blue tones, respectively. G, 3D Voronoi tessellation of neighboring cells (Methods). H, Definition of time between divisions τD and division cycle n. I, Ordered divisions indicate that cells follow specific division rules. In contrast, the cell division axis is randomly oriented for random divisions.