Fig 5. Tests of signalling mechanisms, juxtacrine and paracrine, in the GFP signals.

Juxtacrine signalling is tested in (a)—(c) with geodesic distance (d_G) in the subset of cell pairs that are within a given Euclidean distances (d_E) range, while paracrine signalling is tested in (e)—(f) with Euclidean distances in the subset of cell pairs that have geodesic distances larger than 1. For both signalling modes, a decline to the right in the median regression line suggests the presence of each mode. From the p-values (S1 Table) we conclude the dominance of juxtacrine signalling. The cell pairs characterised by d_G = 1 in (d) are pairs of cells in direct contact. The clear decline in their trend line suggests that the juxtacrine signalling is stronger when there is a larger contact area assuming that, for these cell pairs, greater contact area is correlated with smaller Euclidean distance (i.e. if two cells, each assumed to have a ball shape of a similar diameter, are in contact, the shorter the inter-centroid distance, the larger the contact area).