Telomere length and chromosomal instability in mammalian cells exposed to Low- and High-LET radiations.

Telomeres are specialized nucleoprotein complexes that serve as protective caps of linear eukaryotic chromosomes. The loss of the ends chromosomes due to these un-rejoined DSBs may not be lethal to the cell, but may instead result in the loss of functional telomeres, chromosome fusion, and initiation of breakage/fusion/bridge cycle-induced chromosome instability.The telomeres also partecipate in process of chromosomal repair, as evidenced by “de novo” synthesis of telomere repeats at DSBs and by the capacity of telomeres to bound the essential components of the DNA repair machinery.Based on the observation that high-LET radiations efficientely induce chromosome aberrations, we tested whether low energy protons were able to affect telomere structure. Human primary fibroblasts (HFFF2) and mouse embryonic fibroblasts (MEFs) were irradiated with 4 Gy of 31 keV/um of protons at the radiobiology facility at the 7 MV Van de Graaff CN of the INFN-LNL. Experiments with X-rays were also carried out. Cells were fixed after either 24 hrs or 15 days from treatment. Before harvesting, chromosomes were allowed to condense throught 30’ incubation with Calyculin-A, an agent able to induce premature chromosome condensation. To evaluate radiation-induced alterations of telomere length, Q-FISH staining was performed on condensed chromosomes and interphase nuclei with fluorescent PNA telomeric probe and telomere size was analysed with TFL-TELO software. Preliminary results will be presented and discussed.