GENOMICS 2,257-262 (1988) SHORT COMMUNICATION Genes on Chromosomes 1 and 4 in the Mouse Are Associated with Repair of Radiation-Induced Chromatin Damage MICHAEL POTTER,* KATHERINE K. SArwoRD,t RAM PARSHAD,* ROBERT E. TARONE,!~ FLOYD M. PRIcE,t BEVERLY MOCK,* AND KONRAD HUPPI* *Laboratory of Genetics, Wboratory of Cellular and Molecular Biology, and SBiostatistics Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892; and *Department of Pathology, Howard University College of Medicine, Washington, D.C. 20059 Received November 1, 1987; revised March 30, 1988 Early-passage skin fibroblasts from different inbred and congenic strains of mice were X-irradiated (1 Gy), and the number of chromatid breaks was de- termined at 2.0 h after irradiation. The cells from DBAISN, C3H/HeN, STWA, CS’IBLIBN, BALBlcJ, and AKR/N had 25 to 42 chromatid breaks per 100 metaphase cells (e5cient repair phenotype). NZB/NJ had >78 and BALBlcAn had 87 to 110 chromatid breaks per 100 cells (ine5cient repair phenotype). Differences between BALB/cAn and BALBlc.DBAI2 congenic strains which carry less than 1% of the DBA/2 genome indicate that two genes, one on chro- mosome 1 linked to bcl-2-Pep-3 and the other on chromosome 4 closely linked to h-2, affect the e5- ciency with which the cells repair radiation-induced chromatin damage. O1BBSAcademic Prees,Inc. Radiations associated with intracellular hydroxyl radical (DH) formation, like X-rays and visible light, induce an array of lesions in chromatin including DNA strand breaks, purine and pyrimidine base mod- ifications, and DNA-protein crosslinks (Friedberg, 1985). This damage must be repaired to maintain chromosomal and genetic integrity. A large number of different genes and their products participate in these recovery processes (Cleaver, 1986). The spontaneous development of chromosomal breaks and aberrations is associated with several au- tosomal recessive diseases in man such as ataxia tel- angiectasia, Bloom syndrome, and Fanconi’s anemia (see Friedberg, 1985) and also in certain strains or stocks of mice such as sublines of inbred NZB/Bl (Fialkow et al., 1973; Emerit et al., 1980a,b), the wasted mutant mouse (Shulz et aZ., 1982; Inoue et aZ., 1986), and mice from Rimac Valley, Peru (Wallace, 1971, 1985). The genes responsible for these condi- tions may be mutant forms of genes whose products normally participate in the maintenance of chromo- somal integrity. Because inbred mice are homoxygous at virtually all autosomal loci, they may fortuitously carry recessive alleles of genes whose products are less efficient in restoring chromosomal integrity after exposure to DNA-damaging agents. In previous studies on both mouse and human cells, we have shown that the number of chromatid gaps or breaks per cell at 1.5 h after X-irradiation is an indi- cator of the efficiency of DNA repair (Parshad et al., 1980, 1982a,b, 1983, 1985; Sanford et aZ., 1985; Gantt et al., 1986, 1987). Lesions found in chromatids at metaphase following X-irradiation reflect damage in- curred during the Gz period of the cell cycle (Hittle- man, 1982). In the present study we have examined the responses of cells from different inbred strains of mice to X-rays (1 Gy) and have found two phenotypes based on the number of chromatid breaks observed 2.0 h after irradiation, one reflecting efficient and the other inefficient repair. Two skin fibroblast lines, each from a different mouse, were established for each mouse strain except STS/A, NZB/NJ, and DBAIBN. In these only a single line was established. Cells were predominantly diploid and were tested in the second passage with three ex- ceptions. The DBA/ON cell line was tested twice at the 2nd and 6th passages. Prior to irradiation, the cells were grown for at least 1 week in Pyrex T-flasks to adapt them to glass substrate. Leighton tubes, each containing a 9 X 50-mm cover- slip (No. 1 thickness; Bellco Glass Co., Vineland, NJ), were inoculated with 10’ cells in 2 ml of culture me- dium, Dulbecco’s modified MEM with 10% fetal bo- vine serum. Culture medium was renewed 24 h later. After 48 h incubation, cultures were irradiated by means of two Phillips RT250 opposing therapeutic 257 oa00-7643188$3.00 Copyright 0 1988 by Academic Press, Inc. All rights of reproduction in any form reserved.