Spherical bodies and fibrillar centers in hepatic cell nucleoli of rats treated with D-galactosamine.

Inhibition of rDNA transcription leads to segregation of nucleolar components 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 component, migrated to the nucleolar periphery, and coalesced into large spherical bodies. The latter represented a compartment of the granular component although there were some cytochemical differences. The spherical bodies detached from nucleoli and converted into clusters of interchromatin granules. The matrix substance of the spherical bodies formed filaments interconnecting the granules within the clusters. Nucleolar perichromatin-like granules were released continually from the periphery of spherical bodies before their detachment from nucleoli. The observations suggested that growth-arrested molecules of pre-rRNA synthesized in the initial stage of D-galactosamine action were stored in the nucleoplasm as interchromatin and perichromatin-like granules. The use of antimonate-osmium fixation demonstrated the presence of presumptive fibrillar centers of rapidly increasing density which coalesced with each other, migrating to the nucleolar periphery. At the final stage of nucleolar alterations a single presumptive fibrillar center occupied one of the poles of the nucleolar remnants.