title: Melanogenesis and evidence for melanosome transport to the plasma membrane in a CD83 teleost leukocyte cell line.
abstract: Visceral organs of ectothermic vertebrates harbour melanin-containing leukocytes termed melanomacrophages. These cells are thought to participate in immune reactions and free-radical trapping. In teleosts, the melanin-producing ability of melanomacrophages has hitherto not been confirmed by molecular techniques. Here, a leukocyte marker and the apparatus for melanosome production and transport were investigated in an Atlantic salmon (Salmo salar) pronephros-derived mononuclear leukocyte (SHK-1) cell line. The SHK-1 cells expressed transcripts specific for a mammalian CD83 homologue, a standard surface marker for activated or differentiated dendritic cells, and dopachrome tautomerase/tyrosinase-related protein-2, a melanocyte specific enzyme essential for melanin production. Reduction potential of melanin or its precursors was demonstrated histochemically after prolonged cultivation. Ultrastructural investigations revealed tyrosinase and acid phosphate activity in identical organelles and BSA-gold co-localized with multilamellar melanosomes after 2 h internalization. Apparently, melanosomes were transported and released through periodically occurring tubules fusing with the plasma membrane. Video monitoring revealed filopodia and macropinocytosis. These results showed that the SHK-1 cell line is capable of melanogenesis and melanosome secretion. Melanin-producing cells in teleost pronephros may represent a distinct CD83(+) leukocyte population consisting of phylogenetically relict multifunctional cells. This is the first report of a melanin-producing leukocyte cell-line.
authors.affiliation: Institute of Basic Sciences and Aquatic Medicine, Norwegian School of Veterinary Science, Oslo. erlend.haugarvoll@veths.no
authors.forename: Erlend
authors.initials: E
authors.lastname: Haugarvoll
authors.forename: Jim
authors.initials: J
authors.lastname: Thorsen
authors.forename: Morten
authors.initials: M
authors.lastname: Laane
authors.forename: Qirong
authors.initials: Q
authors.lastname: Huang
authors.forename: Erling Olaf
authors.initials: EO
authors.lastname: Koppang
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000235:genetics / Q000378:metabolism*; D001483:Base Sequence; D001692:Biological Transport; D002460:Cell Line; D002462:Cell Membrane / Q000502:physiology*; D007136:Immunoglobulins / Q000235:genetics / Q000378:metabolism*; D019746:Intramolecular Oxidoreductases / Q000378:metabolism; D007962:Leukocytes / Q000166:cytology* / Q000502:physiology; D008543:Melanins / Q000096:biosynthesis* / Q000502:physiology; D020460:Melanosomes / Q000502:physiology* / Q000648:ultrastructure; D008562:Membrane Glycoproteins / Q000235:genetics / Q000378:metabolism*; D008870:Microtubules; D008969:Molecular Sequence Data; D014442:Monophenol Monooxygenase / Q000378:metabolism; D012474:Salmon / Q000502:physiology; D022161:Transport Vesicles / Q000502:physiology / Q000648:ultrastructure; D000097802:CD83 Antigen
chemical_list: D015703:Antigens, CD; D007136:Immunoglobulins; D019746:Intramolecular Oxidoreductases; D008543:Melanins; D008562:Membrane Glycoproteins; D014442:Monophenol Monooxygenase; D000097802:CD83 Antigen; C042501:dopachrome isomerase