title: Effects of exogenous MSH on the transformation from phaeo- to eumelanogenesis within C57BL/6J-Ay/a hairbulb melanocytes.
abstract: The extent to which alpha melanocyte-stimulating hormone (MSH) is a true in vivo regulator of melanogenesis in mice is unknown. The objective of this study was to determine if MSH-induced eumelanogenesis in hairbulb melanocytes of yellow (Ay/a) mice mimics the natural program of eumelanogenesis occurring in genetically black (a/a) hairbulb melanocytes. We conducted quantitative transmission electron microscopy on melanosome differentiation within MSH-treated regenerating 9-d hairbulbs of Ay/a and a/a mice. Results of exogenous alpha-MSH injections (5 d at 0.15 mM MSH) showed that the striking visual darkening of hair was accompanied by an incomplete transformation of phaeo- to eumelanogenesis. Ontogenetic data on developmental stages I-IV of 3678 melanosomes based on geometric considerations (length, width, shape, and area) showed that MSH did not induce a complete transformation from spherical phaeomelanosomes to elliptical eumelanosomes. Also, observations on the number of vesiculoglobular bodies and matrix organization reveled that MSH-treated Ay/a melanosomes retained distinct features of phaeomelanogenesis even after 5 d of MSH treatment. Thus, MSH induced a partial but incomplete pattern of eumelanogenesis in regenerating hairbulb melanocytes of Ay/a mice. The continued investigation of the dynamics of melanin synthesis in MSH-induced Ay/a mice melanocytes possessing "mosaic" melanosomes could be productive in understanding fundamental relationships between tyrosinase activity, matrix function, matrix structure, and regulation of melanin (phaeo- and/or eumelanin) synthesis.
authors.affiliation: Department of Biology & Microbiology, South Dakota State University, Brookings 57007.
authors.forename: N H
authors.initials: NH
authors.lastname: Granholm
authors.forename: A W
authors.initials: AW
authors.lastname: Van Amerongen
mesh_terms: D000818:Animals; D005804:Genes, Lethal; D006056:Golgi Apparatus / Q000187:drug effects / Q000648:ultrastructure; D009074:Melanocyte-Stimulating Hormones / Q000494:pharmacology*; D008544:Melanocytes / Q000166:cytology* / Q000187:drug effects / Q000648:ultrastructure; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D008854:Microscopy, Electron; D012038:Regeneration; D012879:Skin Physiological Phenomena
chemical_list: D009074:Melanocyte-Stimulating Hormones