Telomeric structure in cells with chromosome end associations

End-to-end associations of metaphase chromosomes have been observed in a variety of human tumors, ageing cells, and several chromosome instability syndromes. Since telomeres of tumor cells and ageing tissues are often reduced in length, it has been suggested that chromosome end associations may be due to loss of telomeric repeats. We report the molecular structure of telomeres of two human tumor cell lines with frequent end-to-end associations of metaphase chromosomes. These telomeres were shown to be severely reduced compared with most other human cells with functional telomeres. However, we also describe two cell lines with severely shortened telomeres that are not detectably compromised in their function. We suggest that telomeric length is not the only determinant of the fusigenic behavior of human telomeres in tumor cells.