AN IONIZING RADIATION-SENSITIVE CHO MUTANT-CELL LINE - IRS-20 .4. GENETIC COMPLEMENTATION, V(D)J RECOMBINATION AND THE SCID PHENOTYPE

The genetic defect responsible for hypersensitivity of Chinese hamster ovary (CHO) irs-20 cells to ionizing radiation was found to be recess ive in nature and could be complemented to produce wild-type radiosens itivity in irs-20/human hybrids. The radiosensitivities of six hybrid clones were determined based on their colony-forming ability under con tinuous irradiation at 6 cGy/h, A parallel cytogenetic analysis reveal ed a concordance between the presence or absence of human chromosome 8 and the resistant or sensitive phenotype, Confirming evidence was obt ained using human chromosome 8-specific PCR primers, Positive amplific ation was obtained in hybrids with wild-type radiosensitivity, while n o amplification was obtained in sensitive hybrids, Complementation ana lysis between radiosensitive CHO irs-20 and murine scid cell lines was carried out to determine whether the defects leading to their ionizin g radiation hypersensitivity could be corrected by genetic complementa tion in the hybrids. Complementation did not occur, A transient V(D)J recombination assay after the introduction of the RAG1 and RAG2 genes indicated that the V(D)J recombination ability of the CHO irs-20 cells was about 10% of that for the CHO wild-type cells for signal join for mation with an 80% joining fidelity and only 3% of the parental level for coding join formation. These data show that murine scid and irs-2O mutant hamster cells fall into the same complementation group and sho w similar defects in V(D)J recombination. (C) 1997 by Radiation Resear ch Society.