Human ocular melanocytes and retinal pigment epithelial cells differ in their melanogenic properties in vivo and in vitro

Purpose. The vertebrate eye contains both melanocytes and retinal pigment epithelial (RPE) cells. Little is known of the pigmentary behaviour of these embryologically dissimilar cells. The aim of this study was to examine aspects of the pigmentary properties of both cell types in vitro and ex vivo to learn more of the function of these cells.Methods. Sections of normal adult human eye were stained for tyrosinase related protein 1(TRP1), and cultures of RPE cells and choroidal melanocytes were examined immunocytochemi-cally for TRP1 and 2 and enzymatically for tyrosinase activity (by assaying dopa oxidase activity).Results. Over half of the choroidal melanocytes expressed TRP1 ex vivo; in contrast, a very small percentage of RPE cells were TRP1 positive. In vitro, passage 1 to 3 ocular melanocytes expressed TRP1 and TRP2 and had tyrosinase activity, which was influenced by the choice of substrate on which the cells were grown. Tyrosinase activity was highest when cells were grown on fibronectin and plastic...