Figure 2.

The pigment-recipient phenotype. The illustration represents the pigment-recipient phenotype conceptually with epithelial cells appearing cubic and a migrating melanocyte appearing star-shaped. Upon acquiring the phenotype, an epithelial cell defines itself as a melanocyte target cell (indicated by a bull’s-eye; for simplicity, a single target cell is shown). The target cell then emits two types of signals: diffusible signals (green gradient; candidates listed), which induce the melanocyte to migrate towards the target and to extend dendrites, and cell-bound signals (candidates listed on the target cell; some candidates have diffusible forms as well), which distinguish the target from its neighbors, allow pigmentary connections to become hard-wired, and accordingly prompt the melanocyte to “hit the bull’seye.” As indicated by a fence, the melanocyte is prevented from connecting to the target cell’s neighbors, as the neighbors fail to emit pigment-recipient signals and may instead produce anti-pigment-donation signals, which block or repel pigmentary connections. With proper connections in place, the recipient’s signals induce melanogenesis and pigment transfer.