Summary
The pigmented epithelium of Rana pipiens tadpole eyes normally develops at least two types of melanosomes: (1) an elongated melanin granule of relatively homogeneous electron density, and (2) a complex melanosome which has an outer electrondense area and one or more less dense cores. Evidence indicates that complex melanosomes are formed by new melanin enclosing preexisting melanosomes. An organized fibrillar premelanosome is demonstrated with the aid of the antimelanogenic compound phenylthiourea (PTU). These premelanosomes are the developing forms of the elongated melanosomes. There is evidence that the premelanosomes originate in the smooth endoplasmic reticulum. Phenylthiourea blocks melanin synthesis in the premelanosomes; however, removal of the PTU allows pigment deposition. This finding of an organized, fibrillar premelanosome in an amphibian marks the lowest phylogenetic group in which these organelles have been described.
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An Oak Ridge Graduate Fellow from Catholic University of America, Washington, D.C., under appointment from Oak Ridge Associated Universities.
The MAN Program is supported by the National Cancer Institute, the National Institute of General Medical Sciences, the National Institute of Allergy and Infectious Diseases, and the U.S. Atomic Energy Commission.
Oak Ridge National Laboratory is operated by Union Carbide Corporation Nuclear Division for the U.S. Atomic Energy Commission.
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Eppig, J.J. Melanogenesis in amphibians. Z. Zellforsch. 103, 238–246 (1970). https://doi.org/10.1007/BF00337315
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DOI: https://doi.org/10.1007/BF00337315