title: A single double-strand break system reveals repair dynamics and mechanisms in heterochromatin and euchromatin.
abstract: Repair of DNA double-strand breaks (DSBs) must be properly orchestrated in diverse chromatin regions to maintain genome stability. The choice between two main DSB repair pathways, nonhomologous end-joining (NHEJ) and homologous recombination (HR), is regulated by the cell cycle as well as chromatin context.Pericentromeric heterochromatin forms a distinct nuclear domain that is enriched for repetitive DNA sequences that pose significant challenges for genome stability. Heterochromatic DSBs display specialized temporal and spatial dynamics that differ from euchromatic DSBs. Although HR is thought to be the main pathway used to repair heterochromatic DSBs, direct tests of this hypothesis are lacking. Here, we developed an in vivo single DSB system for both heterochromatic and euchromatic loci in Drosophila melanogaster Live imaging of single DSBs in larval imaginal discs recapitulates the spatio-temporal dynamics observed for irradiation (IR)-induced breaks in cell culture. Importantly, live imaging and sequence analysis of repair products reveal that DSBs in euchromatin and heterochromatin are repaired with similar kinetics, employ both NHEJ and HR, and can use homologous chromosomes as an HR template. This direct analysis reveals important insights into heterochromatin DSB repair in animal tissues and provides a foundation for further explorations of repair mechanisms in different chromatin domains.
authors.affiliation: Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA;
authors.forename: Aniek
authors.initials: A
authors.lastname: Janssen
authors.affiliation: Department of Therapeutic Radiology, Yale School of Medicine, New Haven, Connecticut 06510, USA; Department of Experimental Pathology, Yale School of Medicine, New Haven, Connecticut 06510, USA;
authors.forename: Gregory A
authors.initials: GA
authors.lastname: Breuer
authors.affiliation: Division of Gene Regulation, Netherlands Cancer Institute, Amsterdam 1066 CX, the Netherlands;
authors.forename: Eva K
authors.initials: EK
authors.lastname: Brinkman
authors.affiliation: Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA;
authors.forename: Annelot I
authors.initials: AI
authors.lastname: van der Meulen
authors.affiliation: Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA;
authors.forename: Sean V
authors.initials: SV
authors.lastname: Borden
authors.affiliation: Division of Gene Regulation, Netherlands Cancer Institute, Amsterdam 1066 CX, the Netherlands;
authors.forename: Bas
authors.initials: B
authors.lastname: van Steensel
authors.affiliation: Department of Therapeutic Radiology, Yale School of Medicine, New Haven, Connecticut 06510, USA; Department of Experimental Pathology, Yale School of Medicine, New Haven, Connecticut 06510, USA;
authors.forename: Ranjit S
authors.initials: RS
authors.lastname: Bindra
authors.affiliation: Department of Human Science, School of Nursing and Health Studies, Georgetown University Medical Center, Washington, DC 20057, USA;
authors.forename: Jeannine R
authors.initials: JR
authors.lastname: LaRocque
authors.affiliation: Biological Systems and Engineering Division, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA; Department of Molecular and Cell Biology, University of California at Berkeley, Berkeley, California 94720, USA.
authors.forename: Gary H
authors.initials: GH
authors.lastname: Karpen
mesh_terms: D000818:Animals; D003584:Cytological Techniques; D053903:DNA Breaks, Double-Stranded; D004260:DNA Repair / Q000502:physiology*; D004331:Drosophila melanogaster / Q000166:cytology / Q000235:genetics*; D022041:Euchromatin / Q000235:genetics*; D006570:Heterochromatin / Q000235:genetics*; D059765:Homologous Recombination; D007814:Larva
chemical_list: D022041:Euchromatin; D006570:Heterochromatin
keywords: Drosophila; NHEJ; cell cycle; heterochromatin; homolog; recombination repair