An anchorage nuclear structure for telomeric DNA repeats in HeLa cells

Using either a biotinylated peptide nucleic acid (PNA) oligomer or a digoxigenin-labeled double-stranded DNA probe, we determined the distribution of the telomeric DNA repeats in HeLa cells by in-situ hybridization at the ultrastructural level. The telomeric DNA was found at the periphery of previously unrecognized roundish nuclear structures, distributed throughout the nucleoplasm. The levels of association of the telomeric DNA with these structures was investigated by exposure of cells to a detergent-containing hypotonic solution which only preserves tightly linked components. The telomeric DNA repeats stayed associated with their anchorage structures following spreading apart of nucleoproteins. Because changes in cellular DNA topology are associated with the intranuclear development of herpes simplex virus type 1 (HSV-1) and adenovirus type 5 (Ad5) in HeLa cells, we examined the distribution of telomeric DNA when cellular DNA is pushed toward the nuclear border. The circular telomeric complexes were morphologically unmodified; however, as a result of the partition of cellular and viral DNA in two concentric compartments, they migrated towards the nuclear border, along with the compressed cellular chromatin. Taken together, our results exemplify the unique organization of the telomeric DNA, which is coiled around a central core of a diameter of 120 nm and can therefore be clearly distinguished from the bulk of the cellular chromatin.