WWP2 ubiquitylates RNA polymerase II for DNA-PK-dependent transcription arrest and repair at DNA breaks.

DNA double-strand breaks (DSBs) at RNA polymerase II (RNAPII) transcribed genes lead to inhibition of transcription. The DNA-dependent protein kinase (DNA-PK) complex plays a pivotal role in transcription inhibition at DSBs by stimulating proteasome-dependent eviction of RNAPII at these lesions. How DNA-PK triggers RNAPII eviction to inhibit transcription at DSBs remains unclear.

Poly(ADP-ribosyl)ation links the chromatin remodeler SMARCA5/SNF2H to RNF168-dependent DNA damage signaling.

Ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) arising in native chromatin elicit an RNF8/RNF168-dependent ubiquitylation response, which triggers the recruitment of various repair factors. Precisely how this response is regulated in the context of chromatin remains largely unexplored. Here, we show that SMARCA5/SNF2H, the catalytic subunit of ISWI chromatin remodeling complexes, is recruited to DSBs in a poly(ADP-ribose) polymerase 1 (PARP1)-dependent manner.

Meiosis in mice without a synaptonemal complex.

The synaptonemal complex (SC) promotes fusion of the homologous chromosomes (synapsis) and crossover recombination events during meiosis. The SC displays an extensive structural conservation between species; however, a few organisms lack SC and execute meiotic process in a SC-independent manner. To clarify the SC function in mammals, we have generated a mutant mouse strain (Sycp1(-/-)Sycp3(-/-), here called SC-null) in which all known SC proteins have been displaced from meiotic chromosomes.

The NuRD chromatin-remodeling complex regulates signaling and repair of DNA damage.

Cells respond to ionizing radiation (IR)-induced DNA double-strand breaks (DSBs) by orchestrating events that coordinate cell cycle progression and DNA repair. How cells signal and repair DSBs is not yet fully understood. A genome-wide RNA interference screen in Caenorhabditis elegans identified egr-1 as a factor that protects worm cells against IR.

Rad51C is essential for embryonic development and haploinsufficiency causes increased DNA damage sensitivity and genomic instability.

Homologous recombination is essential for repair of DNA interstrand cross-links and double-strand breaks. The Rad51C protein is one of the five Rad51 paralogs in vertebrates implicated in homologous recombination. A previously described hamster cell mutant defective in Rad51C (CL-V4B) showed increased sensitivity to DNA damaging agents and displayed genomic instability.

A novel radiosensitive SCID patient with a pronounced G(2)/M sensitivity.

V(D)J rearrangement in lymphoid cells involves repair of double-strand breaks (DSBs) through non-homologous end joining (NHEJ). Defects in this process lead to increased radiosensitivity and severe combined immunodeficiency (RS-SCID). Here, a SCID patient, M3, is described with a T(-)B(+)NK(+) phenotype but without causative mutations in CD3delta, epsilon, zeta or IL7Ralpha, genes specifically involved in T cell development.

Increased DNA damage sensitivity of Cornelia de Lange syndrome cells: evidence for impaired recombinational repair.

Cornelia de Lange syndrome (CdLS) is a rare dominantly inherited multisystem disorder affecting both physical and mental development. Heterozygous mutations in the NIPBL gene were found in about half of CdLS cases. Scc2, the fungal ortholog of the NIPBL gene product, is essential for establishing sister chromatid cohesion.

Schizosaccharomyces pombe Rad22A and Rad22B have similar biochemical properties and form multimeric structures.

The Saccharomyces cerevisiae Rad52 protein has a crucial role in the repair of DNA double-strand breaks by homologous recombination. In vitro, Rad52 displays DNA binding and strand annealing activities and promotes Rad51-mediated strand exchange. Schizosaccharomyces pombe has two Rad52 homologues, Rad22A and Rad22B.

Identification of conserved pathways of DNA-damage response and radiation protection by genome-wide RNAi.

Ionizing radiation is extremely harmful for human cells, and DNA double-strand breaks (DSBs) are considered to be the main cytotoxic lesions induced. Improper processing of DSBs contributes to tumorigenesis, and mutations in DSB response genes underlie several inherited disorders characterized by cancer predisposition. Here, we performed a comprehensive screen for genes that protect animal cells against ionizing radiation.

Two levels of interference in mouse meiotic recombination.

During meiosis, homologous chromosomes (homologs) undergo recombinational interactions, which can yield crossovers (COs) or noncrossovers. COs exhibit interference; they are more evenly spaced along the chromosomes than would be expected if they were placed randomly. The protein complexes involved in recombination can be visualized as immunofluorescent foci.

Inactivation of RAD52 aggravates RAD54 defects in mice but not in Schizosaccharomyces pombe.

RAD52 and RAD54 genes from Saccharomyces cerevisiae are required for double-strand break repair through homologous recombination and show epistatic interactions i.e., single and double mutant strains are equally sensitive to DNA damaging agents.

Mouse Sycp1 functions in synaptonemal complex assembly, meiotic recombination, and XY body formation.

In meiotic prophase, synaptonemal complexes (SCs) closely appose homologous chromosomes (homologs) along their length. SCs are assembled from two axial elements (AEs), one along each homolog, which are connected by numerous transverse filaments (TFs). We disrupted the mouse gene encoding TF protein Sycp1 to analyze the role of TFs in meiotic chromosome behavior and recombination.

Ionizing radiation-induced foci formation of mammalian Rad51 and Rad54 depends on the Rad51 paralogs, but not on Rad52.

Homologous recombination is of major importance for the prevention of genomic instability during chromosome duplication and repair of DNA damage, especially double-strand breaks. Biochemical experiments have revealed that during the process of homologous recombination the RAD52 group proteins, including Rad51, Rad52 and Rad54, are involved in an essential step: formation of a joint molecule between the broken DNA and the intact repair template. Accessory proteins for this reaction include the Rad51 paralogs and BRCA2.

Lig4 and rad54 are required for repair of DNA double-strand breaks induced by P-element excision in Drosophila.

Site-specific double-strand breaks (DSBs) were generated in the white gene located on the X chromosome of Drosophila by excision of the w(hd) P-element. To investigate the role of nonhomologous end joining (NHEJ) and homologous recombination (HR) in the repair of these breaks, the w(hd) P-element was mobilized in flies carrying mutant alleles of either lig4 or rad54. The survival of both lig4- and rad54-deficient males was reduced to 25% in comparison to the wild type, indicating that both NHEJ and HR are involved in the repair P-induced gaps in males.

Genetic steps of mammalian homologous repair with distinct mutagenic consequences.

Repair of chromosomal breaks is essential for cellular viability, but misrepair generates mutations and gross chromosomal rearrangements. We investigated the interrelationship between two homologous-repair pathways, i.e.

Disruption of Drosophila Rad50 causes pupal lethality, the accumulation of DNA double-strand breaks and the induction of apoptosis in third instar larvae.

The Rad50/Mre11/Nbs1 protein complex has a crucial role in DNA metabolism, in particular in double-strand break (DSB) repair through homologous recombination (HR). To elucidate the role of the Rad50 protein complex in DSB repair in a multicellular eukaryote, we generated a Rad50 deficient Drosophila strain by P-element mediated mutagenesis. Disruption of Rad50 causes retarded development and pupal lethality.

The Drosophila melanogaster DNA Ligase IV gene plays a crucial role in the repair of radiation-induced DNA double-strand breaks and acts synergistically with Rad54.

DNA Ligase IV has a crucial role in double-strand break (DSB) repair through nonhomologous end joining (NHEJ). Most notably, its inactivation leads to embryonic lethality in mammals. To elucidate the role of DNA Ligase IV (Lig4) in DSB repair in a multicellular lower eukaryote, we generated viable Lig4-deficient Drosophila strains by P-element-mediated mutagenesis.

CTG repeat instability and size variation timing in DNA repair-deficient mice.

Type 1 myotonic dystrophy is caused by the expansion of an unstable CTG repeat in the DMPK gene. We have investigated the molecular mechanisms underlying the CTG repeat instability by crossing transgenic mice carrying >300 unstable CTG repeats in their human chromatin environment with mice knockout for genes involved in various DNA repair pathways: Msh2 (mismatch repair), Rad52 and Rad54 (homologous recombination) and DNA-PKcs (non-homologous end-joining). Genes of the non-homologous end-joining and homologous recombination pathways did not seem to affect repeat instability.

Induction of epithelial tumors in Drosophila melanogaster heterozygous for the tumor suppressor gene wts.

The imaginal disk cells of Drosophila have a cell cycle that is very similar to that of mammalian cells. Data concerning factors inducing tumors in these cells may directly relate to the risk of these factors for inducing cancer in humans. One of the genes involved in the regulation of cell cycle control is wts (warts), the Drosophila homolog of the mammalian tumor suppressor gene LATS1.

DNA double-strand break repair by homologous recombination.

The induction of double-strand breaks (DSBs) in DNA by exposure to DNA damaging agents, or as intermediates in normal cellular processes, constitutes a severe threat for the integrity of the genome. If not properly repaired, DSBs may result in chromosomal aberrations, which, in turn, can lead to cell death or to uncontrolled cell growth. To maintain the integrity of the genome, multiple pathways for the repair of DSBs have evolved during evolution: homologous recombination (HR), non-homologous end joining (NHEJ) and single-strand annealing (SSA).

Nuclear dynamics of RAD52 group homologous recombination proteins in response to DNA damage.

Recombination between homologous DNA molecules is essential for the proper maintenance and duplication of the genome, and for the repair of exogenously induced DNA damage such as double-strand breaks. Homologous recombination requires the RAD52 group proteins, including Rad51, Rad52 and Rad54. Upon treatment of mammalian cells with ionizing radiation, these proteins accumulate into foci at sites of DNA damage induction.

Differential expression and requirements for Schizosaccharomyces pombe RAD52 homologs in DNA repair and recombination.

In fission yeast two RAD52 homologs have been identified, rad22A(+) and rad22B(+). Two-hybrid experiments and GST pull-down assays revealed physical interaction between Rad22A and Rad22B, which is dependent on the N-terminal regions. Interaction with Rhp51 is dependent on the C-terminal parts of either protein.