The salt-and-pepper pattern in mouse blastocysts is compatible with signalling beyond the nearest neighbours.

Embryos develop in a concerted sequence of spatio-temporal arrangements of cells. In the preimplantation mouse embryo, the distribution of the cells in the inner cell mass evolves from a salt-and-pepper pattern to spatial segregation of two distinct cell types. The exact properties of the salt-and-pepper pattern have not been analysed so far. We investigate the spatio-temporal distribution of NANOG and GATA6 expressing cells in the ICM of the mouse blastocysts with quantitative three-dimensional single cell-based neighbourhood analyses. A combination of spatial statistics and agent-based modelling reveals that the cell fate distribution follows a local clustering pattern. Using ordinary differential equations modelling, we show that this pattern can be established by a distance-based signalling mechanism enabling cells to integrate information from the whole inner cell mass into their cell fate decision. Our work highlights the importance of longer-range signalling to ensure coordinated decisions in groups of cells to successfully build embryos.