The production of pigment involves several signaling molecules essential for the proper development and function of melanocytes. Lethal yellow mice (Ay) have a non-functional MC1R pathway leading to the production of pheomelanin in the hair. Doxycycline (dox) inducible transgenic mice that express Edn3 under the keratin 5 promoter Tg(KRT5-Edn3)#Kosl showed hyperpigmentation of the skin and coat. Tg(KRT5-Edn3)#Kosl darkened the coat color of Ay mice. We hypothesize that EDN3 compensates for the absence of MC1R signaling by upregulating melanogenic genes. To test if continuous transgenic Edn3 expression is required to maintain a dark pigmentation phenotype in Ay mice, dox was administered to newborn pups, deactivating transgenic Edn3 expression. After 6 weeks of dox treatment, the coat color of Ay Tg(KRT5-Edn3)#Kosl mice was similar to those of Ay littermates. The comparative analysis of dorsal hairs from Ay and Ay Tg(KRT5-Edn3)#Kosl mice using high performance liquid chromatography showed that transgenic Edn3 expression significantly increased both eumelanin and pheomelanin in Ay mice. The number of melanocytes in hair follicles of Tg(KRT5-Edn3)#Kosl mice as evidenced by immunofluorescence with an antibody against tyrosinase related protein 1 was similar to that of non-transgenic littermates. Gene expression analysis of the hair bulbs of Ay Tg(KRT5-Edn3)#Kosl mice showed that EDN3 up regulates the expression of melanogenic genes such as tyrosinase. Our results indicate that the paracrine expression of Edn3 from keratinocytes is capable of generating and maintaining a dark coat color in the absence of a functional MC1R pathway by the regulation of melanogenic genes.
J. P. was supported by NIH/NIGMS R25 GM061347. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.