Chromosomal mutations and chromosome loss measured in a new human–hamster hybrid cell line, A LC: studies with colcemid, ultraviolet irradiation, and 137Cs γ-rays

Abstract

Small mutations, megabase deletions, and aneuploidy are involved in carcinogenesis and genetic defects, so it is important to be able to quantify 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 hamster–human hybrid cell line A L. S1 − mutants have lost expression of 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 cytotoxicity assay in which S1 + cells are killed and S1 − cells survive. 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 entire chromosome 11 die and escape detection. To circumvent this, we fused A L with Chinese hamster ovary (CHO) cells to produce a new hybrid, A LC, 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 studies with colcemid ®, 137Cs γ-radiation and UV 254 nm light. Colcemid induced 1000 more S1 − mutants per unit dose in A LC than in A L; the increase for UV 254 nm light was only two-fold; and the increase for 137Cs γ-rays was 12-fold. The increase in S1 − mutant fraction in A LC cells treated with colcemid and 137Cs γ-rays were largely due to chromosome loss and 11p deletions often containing a breakpoint within the centromeric region.