Rescue of marker phenotypes mediated by somatic cell hybridization

The effect of irradiation prior to virus-induced cell fusion on the frequency of hybrid production has been measured as a function of radiation dose. The Chinese hamster line wg3h (HGPRT-) was crossed with the TK- mutants; Chinese hamster A23 or mouse 3T34E, and hybrids were selected in HAT medium. Irradiation of one (marker rescue) or both (mutual rescue) partners before fusion yielded qualitatively different results. After X-irradiation marker rescue curves were of single-hit type, with D0 values about five-fold greater than the irradiated parent cell. Mutual rescue curves were of the multi-hit type, with zero-dose extrapolation value (n) greater than that of the more resistant partner, but no significant alteration in D0. Qualitatively similar results were obtained after U.V.-irradiation, but the probability of rescue per surviving parent cell was higher after U.V. than after X-rays. With both forms of radiation, reciprocal marker rescue curves were not significantly different. Control experiments showed that mutual rescue was not an artefact either of sensitization of parent cells due to TK- or HGPRT- mutations, or of the enhancement of recovery by feeder layers resulting from high-density mutant populations killed with graded radiation doses and HAT selection. Analysis of heterokaryon frequencies within 18 hours of fusion demonstrated that radiation doses up to four lethal hits, given to one or both parents of the cross wg3h x A23, did not increase heterokaryon formation.