Genetic control of signal transduction in mouse melanocytes

At the final step of melanocyte differentiation in mouse hair follicles, the cells produce melanin. The type of melanin they produce is, however, determined by the tissue environment of hair follicles. In wild-type mice, melanocytes located in hair bulbs synthesize eumelanin at the beginning of hair growth. They subsequently produce pheomelanin and finally produce eumelanin again. Therefore, the hair is characterized by a subterminal band of yellow, with the rest of it displaying black. This characteristic is called the agouti pattern and is known to be determined by the wild-type allele, A at the a (agouti) locus, which is considered to function in the follicular cells. Expression of the agouti pattern is altered by genetic substitutions at the a locus and the e (extension) locus. Animals heterozygous for the Ay (lethal yellow) allele exhibit yellow coat color; those homozygous for the e (recessive yellow) also produce yellow hair exclusively. By using an organ culture method, we demonstrated that alpha-MSH and cholera toxin, as well as forskolin, induced eumelanin synthesis in explants from lethal yellow mice (Ay/a). On the other hand, these reagents did not induce eumelanogenesis in the hair follicles of recessive yellow (e/e) mice. Therefore, we assume that the product of the a locus, which probably functions in follicle cells, interacts with alpha-MSH at the alpha-MSH receptor and that the e locus controls the functionality of adenylate cyclase in the membrane of mouse melanocytes.