Elsevier

Developmental Biology

Volume 18, Issue 4, October 1968, Pages 375-390
Developmental Biology

Ultrastructural differences between forming eumelanin and pheomelanin as revealed by the pink-eye mutation in the fowl

https://doi.org/10.1016/0012-1606(68)90047-XGet rights and content

Abstract

The ultrastructural events occurring during melanin formation in the fowl were studied. Melanin precursors are apparently “packaged” in Golgi vesicles. Several of these small vesicles seem to coalesce, forming a large vesicle in which globular bodies become visible. The internal contents of these “multivesiculated bodies” probably contain melanin granule precursors. As longitudinal strands form in the vesicles, they become folded in a zigzag fashion. Melanin is then deposited upon this premelanosome matrix. When eumelanin is synthesized, crosslinks form between the longitudinal strands during the early stages of melanin deposition. Melanin is deposited until a melanosome is formed which shows no internal structure.

The pink-eye (pk) mutation retards melanin deposition so that the matrix structure is visible. Premelanosome formation in retinal melanocytes from both normal and pink-eyed embryos was very similar, suggesting that the mutation does not alter matrix structure. The longitudinal strands of the rod-shaped eumelanin premelanosome are coupled by crosslinks that occur every 200 Å. The resulting network is a matting of connected components showing a repeating hexagonal configuration. Each side of a hexagon is 115 Å long. This matting appears rolled up inside the premelanosome membrane when viewed in cross section.

In the ovoid or spherical pheomelanin premelanosomes the zigzag longitudinal strands form but crosslinks are few or absent, resulting in a disorganized matrix. Lighter-than-normal pheomelanin granules show even shorter longitudinal strands and less organization.

References (22)

  • A.S. Breathnach et al.

    Ultrastructure of retinal pigment epithelium of the human fetus

    J. Ultrastruct. Res

    (1966)
  • G. Cleffmann

    Function-specific changes in the metabolism of agouti pigment cells

    Exptl. Cell Res

    (1964)
  • M. Foster

    Mammalian pigment genetics

    Genetics

    (1965)
  • M.S.C. Birbeck

    Electron microscopy of melanocytes: The fine structure of hair bulb premelanosomes

    Ann. N. Y. Acad. Sci

    (1963)
  • J.A. Brumbaugh

    Differentiation of black-red melanin in the fowl: Interaction of pattern genes and feather follicle milieu

    J. Exptl. Zool

    (1967)
  • J.A. Brumbaugh et al.

    A further study of the E pattern locus in the fowl

    Iowa State J. Sci

    (1965)
  • J.G. Carr

    Internal structure of avian melanin granules: An electron microscope study

    Quart. J. Microscop. Sci

    (1957)
  • P. Drochmans

    The fine structure of melanin granules (the early, mature and compound forms)

  • T.B. Fitzpatrick et al.

    Terminology of vertebrate melanin-containing cells, their precursors, and related cells

  • K.M. Halprin et al.

    Human pigmentation: The role of glutathione

  • F.B. Hutt

    Genetics of the Fowl

    (1949)
  • Cited by (39)

    • New insight into melanin for food packaging and biotechnology applications

      2022, Critical Reviews in Food Science and Nutrition
    View all citing articles on Scopus

    Contribution number 394 of the Department of Zoology and Physiology of the University of Nebraska.

    View full text