title: Filopodia are conduits for melanosome transfer to keratinocytes.
abstract: Melanosomes are specialized melanin-synthesizing organelles critical for photoprotection in the skin. Melanosome transfer to keratinocytes, which involves whole organelle donation to another cell, is a unique biological process and is poorly understood. Time-lapse digital movies and electron microscopy show that filopodia from melanocyte dendrites serve as conduits for melanosome transfer to keratinocytes. Cdc42, a small GTP-binding protein, is known to mediate filopodia formation. Melanosome-enriched fractions isolated from human melanocytes expressed the Cdc42 effector proteins PAK1 and N-WASP by western blotting. Expression of constitutively active Cdc42 (Cdc42(V12)) in melanocytes co-cultured with keratinocytes induced a highly dendritic phenotype with extensive contacts between melanocytes and keratinocytes through filopodia, many of which contained melanosomes. These results suggest a unique role for filopodia in organelle transport and, in combination with our previous work showing the presence of SNARE proteins and rab3a on melanosomes, suggest a novel model system for melanosome transfer to keratinocytes.
authors.affiliation: Department of Dermatology, University of Rochester School of Medicine and Dentistry, Rochester, NY, USA. Glynis_Scott@urmc.rochester.edu
authors.forename: Glynis
authors.initials: G
authors.lastname: Scott
authors.forename: Sonya
authors.initials: S
authors.lastname: Leopardi
authors.forename: Stacey
authors.initials: S
authors.lastname: Printup
authors.forename: Brian C
authors.initials: BC
authors.lastname: Madden
mesh_terms: D001692:Biological Transport; D002478:Cells, Cultured; D006801:Humans; D007091:Image Processing, Computer-Assisted; D015603:Keratinocytes / Q000378:metabolism* / Q000648:ultrastructure; D020460:Melanosomes / Q000378:metabolism* / Q000648:ultrastructure; D009419:Nerve Tissue Proteins / Q000096:biosynthesis / Q000378:metabolism; D011494:Protein Kinases / Q000096:biosynthesis / Q000378:metabolism; D011554:Pseudopodia / Q000502:physiology* / Q000648:ultrastructure; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal; D020764:cdc42 GTP-Binding Protein / Q000378:metabolism
chemical_list: D009419:Nerve Tissue Proteins; C495771:WASL protein, human; D051317:Wiskott-Aldrich Syndrome Protein, Neuronal; D011494:Protein Kinases; C036447:protease activated kinase I; D020764:cdc42 GTP-Binding Protein