An electron microscopic study of the formation of cytosomes in a rat kidney adenoma

Abstract

Tissue from four rat kidney adenomas was studied by electron microscopy. Morphologically the tumors were characterized by prominent Golgi apparatus and numerous cytosomes. The Golgi system consisted of saccules, vacuoles, and vesicles. Some of the vesicles had electron transparent contents, while others contained granular, electron dense materials. Numerous transitional forms between the latter and small cytosomes were seen. Cytochemical demonstration of acid phosphatase activity was performed, using a modification of the Gomori lead phosphate technique. Reaction product was encountered in cytosomes, in small vesicles in the Golgi region, and in vesicles without apparent relationship to the Golgi membranes. Reaction product was also found inside membrane-bounded elements resembling cisternae of smooth endoplasmic reticulum, and occasional pictures were encountered suggesting segregation of a small part of cytoplasm by these membranes. The findings indicate that cytosomes may originate from vesicles in the Golgi region—morphologically identical with Golgi vesicles, from vesicles budding off from smooth endoplasmic reticulum, and directly from cisternae of smooth endoplasmic reticulum.