LOCALIZATION OF NUCLEIC-ACIDS IN HEPATOCYTE NUCLEOLI OF RATS UPON D-GALACTOSAMINE-INDUCED BLOCK OF TRANSCRIPTION

The precise localization of DNA and RNA within rat hepatocyte nucleoli during the process of D-galactosamine-induced nucleolar segregation h as been studied by using sensitive methods for their detection: osmium -ammine staining and terminal deoxynucleotidyl transferase reaction fo r DNA, and immunoelectron microscopy with anti-RNA antibodies, RNase-g old, and autoradiography with tritiated erotic acid for RNA. The block ing of transcription was followed by the disappearance of intranucleol ar condensed chromatin. Agglomerates of thin extended DNA filaments we re found to change their location to the nucleolar periphery and to co alesce with each other. At the last stage of nucleolar segregation the y were concentrated at the pole of the nucleolar fibrillar remnant whi le the rest of the nucleolus did not contain any DNA, No DNA was found in the dense fibrillar component of both intact and treated hepatocyt e nucleoli, During the process of nucleolar segregation the bulk of th e nucleolar RNA was found within the so-called spherical bodies. This RNA appeared to be synthesized shortly before or even after drug admin istration. The results obtained are in agreement with the hypothesis t hat the fibrillar centers are the site of nucleolar transcription. The y also show that uncompleted molecules of pre-rRNA whose synthesis has been blocked are segregated from the rest of nucleolar RNA species in to the spherical bodies. (C) 1996 Academic Press, Inc.