title: Interhomolog recombination and loss of heterozygosity in wild-type and Bloom syndrome helicase (BLM)-deficient mammalian cells.
abstract: Genomic integrity often is compromised in tumor cells, as illustrated by genetic alterations leading to loss of heterozygosity (LOH). One mechanism of LOH is mitotic crossover recombination between homologous chromosomes, potentially initiated by a double-strand break (DSB). To examine LOH associated with DSB-induced interhomolog recombination, we analyzed recombination events using a reporter in mouse embryonic stem cells derived from F1 hybrid embryos. In this study, we were able to identify LOH events although they occur only rarely in wild-type cells (≤2.5%). The low frequency of LOH during interhomolog recombination suggests that crossing over is rare in wild-type cells. Candidate factors that may suppress crossovers include the RecQ helicase deficient in Bloom syndrome cells (BLM), which is part of a complex that dissolves recombination intermediates. We analyzed interhomolog recombination in BLM-deficient cells and found that, although interhomolog recombination is slightly decreased in the absence of BLM, LOH is increased by fivefold or more, implying significantly increased interhomolog crossing over. These events frequently are associated with a second homologous recombination event, which may be related to the mitotic bivalent structure and/or the cell-cycle stage at which the initiating DSB occurs.
authors: Developmental Biology Program, Memorial Sloan-Kettering Cancer Center, New York, NY 10065, USA.
authors: Jeannine R
authors: JR
authors: LaRocque
authors: Jeremy M
authors: JM
authors: Stark
authors: Jin
authors: J
authors: Oh
authors: Ekaterina
authors: E
authors: Bojilova
authors: Kosuke
authors: K
authors: Yusa
authors: Kyoji
authors: K
authors: Horie
authors: Junji
authors: J
authors: Takeda
authors: Maria
authors: M
authors: Jasin
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D033481:Chromosomes, Mammalian / Q000235:genetics*; D003434:Crossing Over, Genetic / Q000235:genetics; D020732:Cytogenetic Analysis; D053903:DNA Breaks, Double-Stranded; D017931:DNA Primers / Q000235:genetics; D018274:Electroporation; D005785:Gene Conversion / Q000235:genetics*; D005822:Genetic Vectors / Q000235:genetics; D019656:Loss of Heterozygosity / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D008969:Molecular Sequence Data; D020641:Polymorphism, Single Nucleotide / Q000235:genetics; D053484:RecQ Helicases / Q000235:genetics*; D017422:Sequence Analysis, DNA
chemical_list: D017931:DNA Primers; C097151:Bloom syndrome protein; D053484:RecQ Helicases