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Electron Microscopic Study of the Mouse Leukemia Virus (Gross) in Organs of Mouse Embryos from Virus-injected and Normal C3Hf Parents¹

From the Cancer Research Unit, Veterans Administration Hospital, Bronx, New York 10468

Ultrathin sections of thymus, spleen, liver, bone marrow, and kidney from embryos of 10 virus-injected and 9 normal noninjected C3Hf female mice were examined in the electron microscope. Leukemia virus particles were present in small numbers in thymus, spleen, liver, and bone marrow of embryos from both virus-injected and normal control parents. They appeared in approximately the same amounts and with similar frequency regardless of whether the embryos were removed from virusinjected or from normal control female mice. Particles were observed budding from lymphocytes, lymphoblasts, and epithelial cells in thymus, from erythroblasts and hemocytoblasts in liver and spleen, and from hemocytoblasts in bone marrow. The virus particles most frequently observed were either budding or of the doughnut-type;² particles containing nucleoids² appeared in only one specimen of embryo thymus from normal noninjected parents. Leukemia virus particles were not observed in kidney tissues from any of the embryos examined.

Examination of embryos from 4 Ak mice and from a normal noninjected BALB/c mouse revealed the presence of virus particles in thymus, spleen, and liver tissues. Thus far, particles were not observed in organs from embryos of 3 virus-injected of 3 normal noninjected Sprague-Dawley rats.

¹ Aided in part by grants from the Damon Runyon Memorial Fund and the American Cancer Society.

² We have preferred using descriptive terms indicating the morphology of observed virus particles rather than arbitrary designation by alphabet letters. According to classification terminology suggested by W. Bernhard (The Detection and Study of Tumor Viruses with the Electron Microscope. Cancer Res, 20: 712–727, 1960), and more recently modified (Classification of Oncogenic RNA Viruses. J. Natl. Cancer Inst., 37: 395–397, 1966), the term "doughnut-type" particle employed in our study corresponds to "A" particle or "immature C" particle, and the term "particlecontaining nucleoid" employed in our study corresponds to "mature C" particle.

Received 2/ 9/67. Accepted 5/29/67.