title: X-rays induce distinct patterns of somatic mutation in fetal versus adult hematopoietic cells.
abstract: There are a variety of mechanisms and pathways whereby cells safeguard their genomes in the face of environmental insults that damage DNA. Whether each of these pathways is equally robust at specific developmental stages in mammals and whether they are also modulated in a tissue-specific manner, however, are unclear. Here, we report that ionizing radiation (IR) produces different types of somatic mutations in fetal cells compared with adult cells of the same lineage. While 1 Gy of X-ray significantly induced intragenic point mutations in T cells of adult mice, no point mutational effect was observed when applied to fetuses. Fetal exposure to IR, on the other hand, led to a significant elevation of mitotic recombination in T cells, which was not observed in adults. Base excision repair (BER) activity was significantly lower in fetal hematopoietic cells than in adult cells, due to a low level of DNA polymerase beta, the rate-limiting enzyme in BER. In fetal hematopoietic cells, this low BER activity, together with a high rate of proliferation, causes X-ray-induced DNA lesions, such as base damage, single strand breaks and double strand breaks, to be repaired by homologous recombination, which we observe as mitotic recombination. Higher BER activity and a relatively lower rate of cell proliferation likely contribute to the significant induction of DNA point mutations in adults. Thus, the mutational response to IR is at least partly determined by the availability of specific repair pathways and other developmentally regulated phenotypes, such as mitotic index.
authors.affiliation: Department of Genetics, Rutgers, The State University of New Jersey, Piscataway, NJ 08854, United States.
authors.forename: Li
authors.initials: L
authors.lastname: Liang
authors.forename: Li
authors.initials: L
authors.lastname: Deng
authors.forename: Marc S
authors.initials: MS
authors.lastname: Mendonca
authors.forename: Yanping
authors.initials: Y
authors.lastname: Chen
authors.forename: Betty
authors.initials: B
authors.lastname: Zheng
authors.forename: Peter J
authors.initials: PJ
authors.lastname: Stambrook
authors.forename: Changshun
authors.initials: C
authors.lastname: Shao
authors.forename: Jay A
authors.initials: JA
authors.lastname: Tischfield
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage; D019951:DNA Polymerase beta / Q000378:metabolism; D004260:DNA Repair; D005260:Female; D005333:Fetus / Q000528:radiation effects; D006413:Hematopoietic System / Q000378:metabolism* / Q000473:pathology; D008297:Male; D051379:Mice; D008809:Mice, Inbred C3H; D008810:Mice, Inbred C57BL; D009154:Mutation / Q000235:genetics*; D011995:Recombination, Genetic; D014965:X-Rays
chemical_list: D004247:DNA; D019951:DNA Polymerase beta