Analysis of restriction enzyme-induced chromosome aberrations in the interstitial telomeric repeat sequences of CHO and CHE cells by FISH.

The interstitial telomeric sequences have been suggested to be more susceptible to chromosome breakage and rejoining. In the present study, we tested this possibility by analysing the behavior of intra-chromosomal telomeric sequences in restriction enzyme-treated CHO and CHE cells. These cell lines show large blocks of internal telomeric repeats adjacent to the centromeric regions of the chromosomes. In CHO cells, (TTAGGG)n repeats are localised only near the centromeric regions of many of the chromosomes while in CHE cells the telomeric repeat sequences are found at both the terminal and centromeric regions of the chromosomes. In CHO cells, 26% of the total aberrations induced by AluI and 22% of those induced by HinfI were found to be involved with internal telomeric repeat sequences. In CHE cells, which possess telomeric repeats at both the terminal and interstitial regions, 39% of the aberrations induced by AluI and PvuII showed telomeric repeat signals. The proportion of acentric fragments with a telomeric repeat signal was higher in CHE than in CHO cells. Some of the damaged cells displayed an intense signal indicating the possible amplification of these repeats by telomerase. These results are in accordance with the suggestion that non-telomeric locations of telomeric repeat sequences are more prone to chromosome breakage and misrepair.