engleski

Telomeres in genomicaly unstable cell line Mia Paca-2

Telomeres are specialized structures found at the ends of eukaryotic chromosomes whose primary structure is the same for all vertebrates (TTAGGG)n. They typically shorten at each cell division, due to the inability of conventional DNA polymerases to replicate the very ends of linear chromosomes. Under normal conditions, cells unable to maintain their telomeres stop dividing as soon as their length fall below critical trashold. Immortal cells undergoing multiple divisions must find an efficient mechanism to maintain telomere length above critical length. Usually this involves activation of expression of TERT, the catalytic subunit of the telomerase complex, which elongates the 3'-ends of linear chromosomes. Following this concept, all immortal cell lines that express telomerase should have detectable telomere sequences at the ends of their chromosomes. Using PNA-FISH method, we analyzed telomeres of MIAPaca-2, human origin immortal cell line that express telomerase. We found that this cell line has very unstable genome with high frequency of chromosome aberrations, so that we could not find two karyograms alike. Accompany to this, we found that 39% of their telomeres do not have detectable telomere repeats. These "undetectable" telomeres were even found on chromatids whose sister chromatids were strongly labeled. Because of high chromosome aberrations we could not follow this phenomena on each particular chromosome, so we used internal PNA probe specific for one chromosome X present in these cells, and analyze its telomere signals. We found high heterogeneity in telomere signals among chromosomes X as well as their sister chromatids. We consider few molecular models by which these cells successfully restore their (almost) lost telomeres in order to continue proliferation.

genome stability; MiaPaca-2

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