The Micromorphology of a Salivary-Gland Tumor of a Mouse Infected with Polyoma Virus2

Abstract

A salivary-gland tumor from a mouse infected at birth with polyoma virus was studied with the electron microscope. Intranuclear, intracytoplasmic, and intercellular particles were observed. Intranuclear particles average 30 mµ and appear to be associated with fine filamentous material. Viruses of 80 mµ similar in structure to leukemia viruses were seen at the cell borders. Both plasma membrane and filamentous material in the cortical cytoplasm appear involved in their formation. Cytoplasmic virus particles associated with mitochondria and inclusion bodies are of size and structure similar to the intranuclear particles. Crystalline aggregates may occur in the inclusion body. Intercellular virus particles include dense forms of 30 mµ identified as polyoma virus, double-membraned forms of 80 or more mµ containing a nucleoid and tentatively identified as leukemia virus, single-membraned forms of 60 to 70 mµ containing an eccentric nucleoid such as the mammary-tumor agent contains, although smaller than the latter, and single-membraned forms of 65 to 70 mµ containing unidentified particles and vesicles. Smaller vesicles of 33 to 52 mµ also occur in the peripheral cytoplasm and intercellular spaces. Their relation to the tumor viruses is undetermined.