PERSISTENCE OF INCREASED LEVELS OF RIBOSOMAL GENE ACTIVITY IN CHO-K1 CELLS TREATED IN-VITRO WITH DEMETHYLATING AGENTS

The rate of ribosomal gene activity was evaluated by silver staining o f the Nucleolus Organisers (NOs) in cultured CHO-K1 cells after a 12h pulse with two demethylating agents (L-ethionine and 5-azacytidine). S ilver staining of the NOs was measured every 24h, from 24 up to 110h a fter seeding. The purpose was to test the hypothesis that drug-induced demethylation is associated to heritable modifications of rDNA activi ty. Ribosomal gene activity was shown to be significantly increased by both agents. The increase persisted throughout the experiments, there by suggesting the heritability of this epigenetic modification. The an alysis of heritable DNA damage or modification is an important task in studying the risk of cancer onset and the mechanisms of cancer induct ion. In these studies two main results were obtained: (i) heritable DN A variations can be induced by both mutational and epigenetic changes; (ii) the modified end-point was not negatively selected.