Comparative Studies of the Nucleoli of Morris Hepatomas, Embryonic Liver, and Aflatoxin B1-treated Liver of Rats

The nucleoli of the adult and embryonic liver, Morris 9121, 8995, 7787, and R-7 hepatomas, and the liver after prolonged aflatoxin B1 treatment were compared with respect to size and ultrastructure. Embryonic liver cells had enlarged nucleoli with well-demarcated fibrillar and granular components of the nucleoli. Cells of Morris Hepatoma 7787, 9121, R-7, and 8995 had enlarged nucleoli. The demarcation of fibrillar and granular components in the nucleolonemas was similar to that of normal liver in the Morris Hepatoma 7787 and was progressively less in Hepatomas 9121, R-7, and 8995. The ratios of the area containing fibrillar components to the total nucleolar area of normal liver, embryonic liver, and Morris hepatomas were within the same range despite differences in the sizes of the nucleoli. The morphologic resemblance of the nucleoli of the 7787 hepatoma to that of the normal liver may be related to the greater similarity of the base composition of rapidly labeled nucleolar RNA of this tumor to that of normal liver than that found for other tumors. In liver cells of aflatoxin B1-treated rats, the enlarged nucleoli resembled those of regenerating liver. From these studies, it appears that the Morris hepatomas contain a spectrum of variation of nucleolar morphology ranging from those of the rapidly growing transplantable tumors to that of normal liver. These data support the view (3) that studies on ultrastructure do not provide diagnostic criteria for tumors, at least with the method of fixation and staining employed in this study.