Membrane-bound intranuclear inclusions in the Leydig cell of the Chinese hamster (Cricetulus griseus)

Membrane-bound intranuclear inclusions have been described, for the first time, in the Leydig cell of the Chinese hamster (Cricetulus griseus). The inclusions were not found in the 1-day-old animal, rarely found prior to sexual maturity, and commonly found in the sexually mature animals. The incidence of inclusions increases with aging. Their size and content varies greatly. They are surrounded by a single membrane and completely enclosed by nucleoplasm. Their close association with nuclear invaginations of cytoplasmic material, and their content of cytoplasmic structures along with some exhibiting the presence of trimetaphosphatase reaction product, suggest a cytoplasmic origin. This phenomenon involves the migration of cytoplasmic structures into the nucleus followed by detachment on the nucleoplasmic side. The presence of the inclusions is not an indication of an abnormality of the Leydig cell. The Leydig cell of the Chinese hamster may be an excellent model to study factors that initiate inclusion formation, and to determine the functional role of membrane-bound intranuclear inclusions.