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Tyrosinase: a developmentally specific major determinant of peripheral dopamine

GRAEME EISENHOFER^*,1, HUA TIAN, COURTNEY HOLMES^*, JUN MATSUNAGA, SUZANNE ROFFLER-TARLOV and VINCENT J. HEARING

Sections on
^* Clinical Neurocardiology and
Neural Development, National Institute of Neurological Disorders and Stroke and
Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland, USA; and
Departments of Neuroscience, Anatomy, and Cell Biology, Tufts University Medical School, Boston, Massachusetts, USA

¹Correspondence: Building 10, Room 6N252, National Institutes of Health, 10 Center Dr. MSC 1620, Bethesda, MD 20892-1620, USA. E-mail: ge{at}box-g.nih.gov

L-3,4-dihydroxyphenylalanine, the immediate precursor of dopamine, can be formed by two enzymes: tyrosine hydroxylase (TH) in catecholamine-producing neurons and chromaffin cells and tyrosinase in melanocytes. In this study we examined whether tyrosinase contributes to production of dopamine. Deficiency of TH caused marked reductions in norepinephrine in albino and pigmented 15-day-old mice. In contrast, peripheral levels of dopamine were reduced only in albino TH-deficient mice and were higher in pigmented than in albino mice, regardless of the presence or absence of TH. We next examined age-related changes in dopamine and cutaneous expression of tyrosinase and melanin in albino and pigmented TH wild-type mice. We found that the differences in peripheral dopamine between pigmented and albino mice disappeared with advancing age following changes in expression and function of tyrosinase. In young animals, tyrosinase was present in epidermis but did not produce detectable melanin. With advancing age, tyrosinase was localized only around hair follicles, melanin synthesis became more pronounced, and dopamine synthesis decreased. The data reveal a previously unrecognized TH-independent major pathway of peripheral dopamine synthesis in young, but not adult, mice. The transient nature of this source of dopamine reflects a developmental switch in tyrosinase-dependent production of dopamine to production of melanin.—Eisenhofer, G., Tian, H., Holmes, C., Matsunaga, J., Roffler-Tarlov, S., Hearing, V. J. Tyrosinase: a developmentally specific major determinant of peripheral dopamine.

Key Words: L-dopa • tyrosine hydroxylase • sympathetic nervous system • melanocyte • melanin

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