U. Schraermeyer et H. Stieve, A NEWLY DISCOVERED PATHWAY OF MELANIN FORMATION IN CULTURED RETINAL-PIGMENT EPITHELIUM OF CATTLE, Cell and tissue research, 276(2), 1994, pp. 273-279
According to a recent hypothesis the melanin granules in the retinal p
igment epithelium of mammals originate from photosensory membrane degr
adation. To test this hypothesis the retinal pigment epithelium of cat
tle was kept in tissue culture and exposed to gold-labelled rod outer
segments. Gold granules were later detected inside phagosomes, melanos
omes and mature melanin granules. Tyrosinase, the key enzyme in melano
genesis, was additionally localized inside phagosomes. These results i
ndicate that in cultured retinal pigment epithelium the matrix of the
melanosome can originate from phagosomes. Therefore, the melanosome is
a specialized lysosome.