Ricerc@Sapienza

Human telomeres are synthesized by the ribonucleoprotein telomerase. The abundance of hTR, the telomerase RNA component, is post-transcriptionally regulated by several enzymes and RNA-binding complexes that cooperate to convert longer hTR precursors to the mature form. A complex balance between 3¿ processing and degradation of hTR isoforms ultimately determines the steady-state levels of mature hTR that is incorporated into telomerase. We found that TGS1, the hypermethylase that converts the hTR 5' mono-methylguanosine cap to a tri-methylguanosine cap (TMG), favors nuclear retention of hTR and limits hTR abundance, thus tuning down telomerase activity. This project is aimed at characterizing the role of TGS1 in the regulation of telomerase biogenesis and activity in human cells, using TGS1 mutant cell lines generated by CRISPR-mediated genome editing. We have evidence that chemical inhibition of TGS1 activity affects telomere length in vivo and will explore the hypothesis that TGS1 inhibitors can be exploited as potential therapeutic tools for the treatment of telomerase insufficiency syndromes caused by reductions in the hTR levels.

In Drosophila, telomerase has been lost and telomeres are elongated by targeted transposition of retroelements at the DNA ends, while a specific capping complex, terminin, protects telomeres independently of sequence. Despite these differences, Drosophila melanogaster proved to be an excellent model system for the identification and characterization of proteins implicated in telomere maintenance, as fly telomeres are also protected by conserved non-terminin proteins, most of which have human counterparts involved in telomere maintenance. We will explore whether the fly homologue of TGS1, DTgs1, which physically interacts with terminin, is required for telomere homeostasis, by investigating its role in the biogenesis and expression of the telomeric retrotransposons Het-A and TART.