Experimental pineocytoma of the Syrian hamster induced by a human papovavirus (JC). A light and electron microscopic study.

The gross, light and electron microscopic features of a pineocytoma of the Syrian hamster (mesocricetus auratus) which had been induced by a human oncogenic virus (JC papovavirus) have been defined. For comparison, adult hamster pineal tissue was studied, and the literature was consulted in regard to other pineal parenchymal tumors, and to pineal cell differentiation during ontogeny and phylogeny. Many differentiated tumor cells contained organelles, such as vesicle-crowned lamellae (synaptic ribbons) and microtubular sheaves, as consistent with adult hamster pineocytes. Some cells showed rudimentary photoreceptor-like differentiation as consistent with fetal hamster pineocytes and with cells seen in the pineal systems of some lower vertebrate species. Such tumor cells had lumen-directed specialized cytoplasmic extensions which, by their richness in mitochondria and presence of centrioles and striated rootlets, resembled inner segments. Extending 9+0 cilia were accompanied by occasional lamellar whorls. Oncogenesis seems to have simulated different stages of hamster pineal ontogeny. This observation would support the theory that the secretory mammalian pineocyte derived phylogenetically from the true photoreceptor cell of the pineal system of fishes and amphibians. The possible influences of host and of virus in the accomplishment of tumor morphology were discussed. This tumor differed considerably in pattern and cell detail from the only other pineocytoma studied previously by electron microscopy. It is the first experimentally induced pineocytoma.