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Electron Microscopic Study of Methylcholanthrene-induced Epidermal Carcinogenesis in Mice: Mitochondrial Dense Bodies and Intracisternal A-Particles¹

Division of Neurosciences, City of Hope Medical Center, Duarte, California 91010 [T. K., E. R.] and Department of Anatomy, Washington University, School of Medicine, St. Louis, Missouri 63110

Electron microscopic observations were made of mouse epidermis during successive stages of methylcholanthrene carcinogenesis through the formation of papillomas and squamous cell carcinomas, and the pertinent changes are discussed. Numerous intramitochondrial dense bodies were found in the papillomas resulting from treatment with methylcholanthrene. A consideration of the results of our own studies and of the reports in the literature suggested that the latter bodies do not have a specific relationship to treatment with the carcinogen or to the carcinogenic process itself, but rather that they may be related to intracellular keratinization and/or keratin synthesis. Intracisternal A-particles were found in large amounts in the squamous cell carcinomas, but were not shown to be oncogenic per se in our experiments. Tumors were produced when cell-free particulates from the squamous cell tumors were injected into newborn mice; these were almost exclusively mammary carcinomas, and the morphology of the virus-like particles contained in them did not resemble that of the intracisternal A-particles. A consideration of the data available did not make it possible to assign to the changes in arginase activity during epidermal carcinogenesis more than a correlative association with the malignant transformation.

¹ Supported in part by Research Grant CA-2568 from the National Cancer Institute, NIH; an NIH General Research Support Award given to the City of Hope Medical Center; and a supporting fund established in the name of Robert F. Kennedy.

² Present address: Chemistry Branch, National Cancer Institute, NIH, Bethesda, Md.

Received 6/27/69. Accepted 10/ 2/69.