TELOMERE LENGTH, CHROMATIN STRUCTURE AND CHROMOSOME FUSIGENIC POTENTIAL

Telomeres are specialized structures at chromosome ends that are thoug ht to function as buffers against chromosome fusion. Several studies s uggest that telomere shortening may render chromosomes fusigenic. We u sed a novel quantitative fluorescence in situ hybridization procedure to estimate telomere length in individual mammalian chromosomes, and G -banding and chromosome painting techniques to determine chromosome fu sigenic potential. All analysed Chinese hamster and mouse cell lines e xhibited shorter telomeres at short chromosome arms than at long chrom osome arms. However, no clear link between short telomeres and chromos ome fusigenic potential was observed, i.e. frequencies of telomeric as sociations were higher in cell lines exhibiting longer telomeres. We s peculate that chromosome fusigenic potential in mammalian cell lines m ay be determined not only by telomere length but also by the status of telomere chromatin structure. This is supported by the observed prese nce of chromatin filaments linking telomeres in Chinese hamster chromo somes and of multibranched chromosomes oriented end-to-end in the muri ne severe combined immunodeficient (SCID) cell line. Multibranched chr omosomes are the hallmark of the human ICF (Immune deficiency, Centrom eric instability, Facial abnormalities) syndrome, characterized by alt erations in heterochromatin structure.