Conceptual representation of fur coloration pattern emergence and implementation. First, a differential distribution of molecular activators (green) and inhibitors (blue) establishes an initial condition that constrains pattern outputs. R-D mechanisms then give rise to spatially distributed patterns of activator and inhibitor molecules. During the early implementation stage, collective cellular behaviors stabilize molecular prepattern information: (i) the latter can become stably retained within cells as epigenetic memory, (ii) initially patterned cells can hand over information to another cell type for safekeeping, and (iii) local morphogenesis can advance tissue to a new stable morpho-functional state. Lastly, late implementation occurs through differential cell activities in molecularly patterned tissue units. Images for Figure 1D were kindly provided with permission by Kelly McGowan and Gregory Barsh.
