CHROMOSOMAL MUTATIONS AND CHROMOSOME LOSS MEASURED IN A NEW HUMAN-HAMSTER HYBRID CELL-LINE, A(L)C - STUDIES WITH COLCEMID, ULTRAVIOLET-IRRADIATION, AND CS-137 GAMMA-RAYS

Small mutations, megabase deletions, and aneuploidy are involved in ca rcinogenesis and genetic defects, so it is important to be able to qua ntify these mutations and understand mechanisms of their creation. We have previously quantified a spectrum of mutations, including megabase deletions, in human chromosome 11, the sole human chromosome in a ham ster-human hybrid cell line A(L). S1(-) mutants have lost expression o f a human cell surface antigen, S1, which is encoded by the M1C1 gene at 11p13 so that mutants can be detected via a complement-mediated cyt otoxicity assay in which S1(+) cells are killed and S1(-) cells surviv e, But loss of genes located on the tip of the short arm of 11 (11p15. 5) is lethal to the A(L) hybrid, so that mutants that have lost the en tire chromosome 11 die and escape detection. To circumvent this, we fu sed A(L) with Chinese hamster ovary (CHO) cells to produce a new hybri d, A(L)C, in which the requirement for maintaining 11p15.5 is relieved , allowing us to detect mutation events involving loss of 11p15.5. We evaluated the usefulness of this hybrid by conducting mutagenesis stud ies with colcemid(R) Cs-137 gamma-radiation and UV 254 nm light. Colce mid induced 1000 more S1(-) mutants per unit dose in A(L)C than in A(L ); the increase for UV 254 nm light was only two-fold; and the increas e for Cs-137 gamma-rays was 12-fold. The increase in S1(-) mutant frac tion in A(L)C cells treated with colcemid and Cs-137 gamma-rays were l argely due to chromosome loss and 11p deletions often containing a bre akpoint within the centromeric region. (C) 1997 Elsevier Science B.V.