SPHERICAL BODIES AND FIBRILLAR CENTERS IN HEPATIC CELL NUCLEOLI OF RATS TREATED WITH D-GALACTOSAMINE

Inhibition of rDNA transcription leads to segregation of nucleolar com ponents and accumulation of dense material of coarse fibrillogranular structure. Fibrillar centers are not always detectable. In the present study D-galactosamine was used to inhibit transcription in rat liver cells. Small dense microspherules detached from the dense fibrillar co mponent, migrated to the nucleolar periphery, and coalesced into large spherical bodies. The latter represented a compartment of the granula r component although there were some cytochemical differences. The sph erical bodies detached from nucleoli and converted into clusters of in terchromatin granules. The matrix substance of the spherical bodies fo rmed filaments interconnecting the granules within the clusters. Nucle olar perichromatin-like granules were released continually from the pe riphery of spherical bodies before their detachment from nucleoli. The observations suggested that growth-arrested molecules of pre-rRNA syn thesized in the initial stage of D-galactosamine action were stored in the nucleoplasm as interchromatin and perichromatin-like granules. Th e use of antimonate-osmium fixation demonstrated the presence of presu mptive fibrillar centers of rapidly increasing density which coalesced with each other, migrating to the nucleolar periphery. At the final s tage of nucleolar alterations a single presumptive fibrillar center oc cupied one of the poles of the nucleolar remnants. (C) 1994 Academic P ress, Inc.