[Ultrastructure of induced yolk sac tumor in the pregnant rats].
By the administration of carcinogens to the fetal membrane of pregnant rats, yolk sac tumors producing AFP was induced. The process of production of such tumors and AFP was studied at the ultrastructural level. Electron microscopy revealed that the structure of the tumor induced extended radiately around the tubal cavity, and the cubical cells were arranged in rows. Microvilli were observed on the cellular surface toward the tubal cavity. The adjacent cells were relatively diffused and an interdigitation was partly observed, but formation of incomplete desmosome was also apparence. The nuclei were generally large, some being irregular in shape. Nucleoli with a thread-like nucleolonema were also observed. There was rich organella in the cytoplasm and mitochondria and r-ER was particularly noted. In the r-ER the intracavity was enlarged containing some substances with moderate density. Some granules with the same density as said substance were present in the cytoplasm. This substance was recognized to be AFP. As the source of the material, rich free-ribosome and glycogen granules were observed around the r-ER with an amorphous substance. Due to the effect of functional collaboration, AFP was produced and accumulated in the r-ER according to the same process as protein synthesis.