title: Involvement of illegitimate V(D)J recombination or microhomology-mediated nonhomologous end-joining in the formation of intragenic deletions of the Notch1 gene in mouse thymic lymphomas.
abstract: Deregulated V(D)J recombination-mediated chromosomal rearrangements are implicated in the etiology of B- and T-cell lymphomagenesis. We describe three pathways for the formation of 5'-deletions of the Notch1 gene in thymic lymphomas of wild-type or V(D)J recombination-defective severe combined immune deficiency (scid) mice. A pair of recombination signal sequence-like sequences composed of heptamer- and nonamer-like motifs separated by 12- or 23-bp spacers (12- and 23-recombination signal sequence) were present in the vicinity of the deletion breakpoints in wild-type thymic lymphomas, accompanied by palindromic or nontemplated nucleotides at the junctions. In scid thymic lymphomas, the deletions at the recombination signal sequence-like sequences occurred at a significantly lower frequency than in wild-type mice, whereas the deletions did not occur in Rag2(-/-) thymocytes. These results show that the 5'-deletions are formed by Rag-mediated V(D)J recombination machinery at cryptic recombination signal sequences in the Notch1 locus. In contrast, one third of the deletions in radiation-induced scid thymic lymphomas had microhomology at both ends, indicating that in the absence of DNA-dependent protein kinase-dependent nonhomologous end-joining, the microhomology-mediated nonhomologous end-joining pathway functions as the main mechanism to produce deletions. Furthermore, the deletions were induced via a coupled pathway between Rag-mediated cleavage at a cryptic recombination signal sequence and microhomology-mediated end-joining in radiation-induced scid thymic lymphomas. As the deletions at cryptic recombination signal sequences occur spontaneously, microhomology-mediated pathways might participate mainly in radiation-induced lymphomagenesis. Recombination signal sequence-mediated deletions were present clonally in the thymocyte population, suggesting that thymocytes with a 5'-deletion of the Notch1 gene have a growth advantage and are involved in lymphomagenesis.
authors.affiliation: Low Dose Radiation Effects Research Project Group, Radiation Hazards Research Group, and Environmental and Toxicological Science Research Group, National Institute of Radiological Sciences, Chiba, Japan. tsujihid@nirs.go.jp
authors.forename: Hideo
authors.initials: H
authors.lastname: Tsuji
authors.forename: Hiroko
authors.initials: H
authors.lastname: Ishii-Ohba
authors.forename: Takanori
authors.initials: T
authors.lastname: Katsube
authors.forename: Hideki
authors.initials: H
authors.lastname: Ukai
authors.forename: Shiro
authors.initials: S
authors.lastname: Aizawa
authors.forename: Masahiro
authors.initials: M
authors.lastname: Doi
authors.forename: Kyoji
authors.initials: K
authors.lastname: Hioki
authors.forename: Toshiaki
authors.initials: T
authors.lastname: Ogiu
mesh_terms: D000818:Animals; D001483:Base Sequence; D045744:Cell Line, Tumor; D019457:Chromosome Breakage; D051747:DNA-Activated Protein Kinase; D004268:DNA-Binding Proteins / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D017353:Gene Deletion; D015321:Gene Rearrangement; D008223:Lymphoma / Q000209:etiology / Q000235:genetics*; D051379:Mice; D008807:Mice, Inbred BALB C; D016513:Mice, SCID; D009381:Neoplasms, Radiation-Induced / Q000209:etiology / Q000235:genetics*; D017346:Protein Serine-Threonine Kinases / Q000172:deficiency / Q000235:genetics / Q000378:metabolism; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface / Q000235:genetics*; D011995:Recombination, Genetic / Q000235:genetics; D015398:Signal Transduction; D013950:Thymus Gland / Q000528:radiation effects; D013953:Thymus Neoplasms / Q000209:etiology / Q000235:genetics*; D014157:Transcription Factors / Q000235:genetics*; D045567:VDJ Recombinases; D014965:X-Rays
chemical_list: D004268:DNA-Binding Proteins; C497762:Notch1 protein, mouse; C499308:Rag2 protein, mouse; D051881:Receptor, Notch1; D011956:Receptors, Cell Surface; D014157:Transcription Factors; C064655:V(D)J recombination activating protein 2; D051747:DNA-Activated Protein Kinase; D017346:Protein Serine-Threonine Kinases; D045567:VDJ Recombinases