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Tyrosinase mRNA, synthesis and activity were measured in the skin during the first 2 weeks of life of C₃H-HeA^vy mice. Tyrosinase mRNA levels were found to peak on days 3–4 and were followed by increases in tyrosinase synthesis and activity which peaked on days 6–7 and 7–8 respectively. These changes in tyrosinase expression were presumably associated with the growth of the first coat of hair that in neonatal C₃H-HeA^vy mice is yellow in colour as a result of the increased proportion of phaeomelanin. By the time hair growth had ceased there was no expression of tyrosinase at both mRNA and protein levels. Daily administration of -melanocyte stimulating hormone (-MSH) enhanced the expression of tyrosinase mRNA transcripts, tyrosinase synthesis and activity. The increase in tyrosinase activity paralleled the change in the amount of tyrosinase, suggesting that the primary action of -MSH is to stimulate new synthesis of the enzyme. This induction of tyrosinase was associated with the growth of hair that was darker in colour than that of the controls and contained an increased proportion of eumelanin. This increase in eumelanin reflected a decrease in phaeomelanin content. It was concluded that, through its actions on the enzyme tyrosinase, -MSH is able to switch the synthesis of phaeomelanin to that of eumelanin in hair follicular melanocytes.

Journal of Endocrinology (1993) 137, 189–195

This article has been cited by other articles:

				G Hunt, C Todd, J. Cresswell, and A. Thody Alpha-melanocyte stimulating hormone and its analogue Nle4DPhe7 alpha-MSH affect morphology, tyrosinase activity and melanogenesis in cultured human melanocytes J. Cell Sci., January 1, 1994; 107(1): 205 - 211. [Abstract] [PDF]