Ultrastructure of the interphase nucleoli of pig embryonic kidney cells during their compensatory hypertrophy and degradation due to local UV microirradiation
Zatsepina, O.V.; Voronkova, L.N.; Sakharov, V.N.; Chentsov, I.S.
Tsitologiia 30(7): 787-794
1988
ISSN/ISBN: 0041-3771 PMID: 3188226 Document Number: 316820
As shown elsewhere, the ultraviolet (UV) irradiation of one of the two nucleoli of the interphase cell nucleus results in inactivation and degradation of the irradiated nucleus and in the compensatory growth and activation of the nonirradiated one. In the present work we studied the ultrastructure of degraded and hypertrophied nucleoli in PK-cells with the aid of serial ultrathin sections. The compensatory hypertrophy of the nucleoli was shown to be accompanied by a significant increase in the number of fibrillar centers (FC) and a decrease in their linear size compared with the control ones; in the degraded nucleoli, the FCs number went down, while the size of FCs increased. Overall, the structural changes of the degraded nucleoli upon their UV microirradiation corresponded to those caused by the action of other known inhibitors of rRNA. The capacity of nucleoli for compensatory hypertrophy indicates that apart from the operating ribosomal genes, the cell also contains latent r-genes which may be activated under extreme conditions so as to sustain the required level of rRNA synthesis. It is suggested that such an activation is accompanied by a "fragmentation" of the original FCs into smaller and more numerous ones.