Expression of the fragile (X) chromosome in an interspecific somatic cell hybrid

Interspecific somatic cell hybrids were constructed between a Chinese hamster lung cell line deficient in hypoxanthine phosphoribosyltransferase and two lymphoblastoid cultures (GM 4025 and GM 3200) from unrelated males affected with the fragile (X) syndrome. Thirteen independent colonies survived selection in hypoxanthine-azaserine, while only one colony survived selection in hypoxanthine-aminopterin-thymidine. One hybrid formed from GM 4025 was found to contain a human X chromosome as the only detectable human chromosome in the majority of cells analyzed. Induction of fragile (X) expression in this hybrid at frequencies up to 20% was achieved by treatments with 5-fluoro-2'-deoxyuridine (5 X 10(-8) M or 1 X 10(-7) M) or methotrexate (5 X 10(-6) or 1 X 10(-5) for 12 h. Use of the somatic cell hybrid system may allow study of the fragile (X) from different patients on a homogeneous xenogeneic background and may provide a better system for characterization of the fragile (X) at the biochemical and molecular level.