Invecchiamento cellulare e riparazione del danno ossidativo nel ciliato Euplotes raikovi: caratterizzazione dei geni specifici per le metionina-solfossido redattasi

Ciliated protozoa represent excellent material to explore the biology of ageing and rejuvenation, since they are both “complex” organisms and “simple” cells directly exposed at the environment and natural selection. Using Euplotes raikovi (a protistan whose life cycle is well characterized), I investigated the molecular resources that enable cells to repair oxidative damage of their vital macromolecules. A complex of six distinct genes that encode two forms, A and B, of methionine sulphoxide redutase (Msr, the enzyme that reduces a residue of methionine sulphoxide to methionine) was identified. The complete structure of two of these genes (designated Er-msrB and Er-msrA/B) was determined including both coding and non-coding regions; the structural analysis of the other four genes (Er-msrA1, Er-msrA2-A, Er-msrA2-B, e Er-msrA2-C) was incomplete. Er-MsrB2 (specified by one of the two open reading frames of the Er-msrA/B gene), Er-MsrB1, and Er-MsrA1 are closely related to Msr’s of other protozoa. In contrast, Er-msrA3 (specified by the second open reading frame of the Er-msrA/B gene) and Er-MsrA2 are phylogenetically related to Msr’s of prokaryotic origin. A further divergence between the Er-msr genes was detected at the functional level. Transcription of the Er-msrB gene is apparently not induced by oxidative stress, whereas transcription of the genes encoding the Msr A forms is specifically enhanced in cells subjected to oxidative stress