title: Double-strand break repair by interchromosomal recombination: an in vivo repair mechanism utilized by multiple somatic tissues in mammals.
abstract: Homologous recombination (HR) is essential for accurate genome duplication and maintenance of genome stability. In eukaryotes, chromosomal double strand breaks (DSBs) are central to HR during specialized developmental programs of meiosis and antigen receptor gene rearrangements, and form at unusual DNA structures and stalled replication forks. DSBs also result from exposure to ionizing radiation, reactive oxygen species, some anti-cancer agents, or inhibitors of topoisomerase II. Literature predicts that repair of such breaks normally will occur by non-homologous end-joining (in G1), intrachromosomal HR (all phases), or sister chromatid HR (in S/G(2)). However, no in vivo model is in place to directly determine the potential for DSB repair in somatic cells of mammals to occur by HR between repeated sequences on heterologs (i.e., interchromosomal HR). To test this, we developed a mouse model with three transgenes-two nonfunctional green fluorescent protein (GFP) transgenes each containing a recognition site for the I-SceI endonuclease, and a tetracycline-inducible I-SceI endonuclease transgene. If interchromosomal HR can be utilized for DSB repair in somatic cells, then I-SceI expression and induction of DSBs within the GFP reporters may result in a functional GFP+ gene. Strikingly, GFP+ recombinant cells were observed in multiple organs with highest numbers in thymus, kidney, and lung. Additionally, bone marrow cultures demonstrated interchromosomal HR within multiple hematopoietic subpopulations including multi-lineage colony forming unit-granulocyte-erythrocyte-monocyte-megakaryocte (CFU-GEMM) colonies. This is a direct demonstration that somatic cells in vivo search genome-wide for homologous sequences suitable for DSB repair, and this type of repair can occur within early developmental populations capable of multi-lineage differentiation.
authors.affiliation: Department of Biology, University of North Carolina-Charlotte, Charlotte, North Carolina, United States of America.
authors.forename: Ryan R
authors.initials: RR
authors.lastname: White
authors.affiliation: Developmental Biology, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, New York, United States of America.
authors.forename: Patricia
authors.initials: P
authors.lastname: Sung
authors.affiliation: Department of Biology, University of North Carolina-Charlotte, Charlotte, North Carolina, United States of America.
authors.forename: C Greer
authors.initials: CG
authors.lastname: Vestal
authors.affiliation: Department of Biology, University of North Carolina-Charlotte, Charlotte, North Carolina, United States of America.
authors.forename: Gregory
authors.initials: G
authors.lastname: Benedetto
authors.affiliation: Department of Biology, University of North Carolina-Charlotte, Charlotte, North Carolina, United States of America.
authors.forename: Noelle
authors.initials: N
authors.lastname: Cornelio
authors.affiliation: Department of Biology, University of North Carolina-Charlotte, Charlotte, North Carolina, United States of America.
authors.forename: Christine
authors.initials: C
authors.lastname: Richardson
mesh_terms: D000818:Animals; D033481:Chromosomes, Mammalian / Q000235:genetics / Q000378:metabolism*; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000502:physiology*; D051379:Mice; D008822:Mice, Transgenic; D009928:Organ Specificity / Q000502:physiology; D011995:Recombination, Genetic / Q000502:physiology*