Telomere associations in interphase nuclei: possible role in maintenance of interphase chromosome topology

The relative sizes of individual telomeres in cultured human cells under co nditions of cell cycling, replicative quiescence, cell transformation and i mmortalization were determined using quantitative fluorescence in situ hybr idization (Q-FISH) with a telomere-specific peptide nucleic acid (PNA) prob e. Results obtained from analysis of telomere length profiles (TLPs), which display the distribution of relative telomere lengths for individual cells , confirmed telomere length heterogeneity at the single cell level and prop ortional shortening of telomere length during replicative aging of virus-tr ansformed cells, TLPs also revealed that some telomeric ends of chromosomes are so closely juxtaposed within interphase nuclei that their fluorescent signals appear as a single spot. These telomeric associations (TAs) were fa r more prevalent in interphase nuclei of noncycling normal and virus-transf ormed cells than in their cycling counterparts. The number of interphase TA s per nucleus observed in late-passage E6/E7-transformed cells did not incr ease during progression to crisis, suggesting that telomere shortening does not increase the frequency of interphase TAs, Furthermore, interphase TAs were rarely observed in rapidly cycling, telomerase-positive, immortalized cells that exhibit somewhat shortened, but stabilized, telomere length thro ugh the activity of telomerase, Our overall results suggest that the number of interphase TAs is dependent more on whether or not cells are cycling th an on telomere length, with TAs being most prominent in the nuclei of repli catively quiescent cells in which nonrandom (even preferred) chromosome spa tial arrangements have been observed. We propose that interphase TAs may pl ay a role in the generation and/or maintenance of nuclear architecture and chromosome positional stability in interphase nuclei, especially in cells w ith a prolonged G(1)/G(0) phase and possibly in terminally differentiated c ells.