Multiple Genetic Pathways Involving the Caenorhabditis elegans Bloom's Syndrome Genes him-6, rad-51, and top-3 Are Needed To Maintain Genome Stability in the Germ Line

摘要: Mutations in three genes encoding human RecQ helicases BLM, WRN, and RecQ4 are associated with distinct clinical disorders namely, Bloom's syndrome (BS), Werner's (WS), Rothmund-Thomson (RTS) (13, 31, 68), respectively. BS is characterized by an elevated risk for a wide variety of cancers, immunodeficiency, slow growth, male sterility, female subfertility (20). Furthermore, cells exhibit hyperrecombination phenotype greatly enhanced reciprocal exchanges between sister chromatids, as well chromatid gaps breaks. These phenotypes consistent recent evidence from Drosophila melanogaster that BLM might be required synthesis-dependent strand annealing (2). WS RTS both cancer predisposition, premature aging (50, 57). The fact patients suffering these syndromes prone to develop cancers shows the importance role played family maintenance genome stability prevention tumorigenesis. The prototypic helicase Escherichia coli RecQ. component RecF pathway, which recombinational repair, essential nearly all non-double-strand break recombination E. (41, 42, 52). Because its activity can unwind DNA at broken ends, protein, together RecJ 5′-3′ nuclease, was proposed act functional analogs RecBCD helicase/nuclease pathway during repair (21). In budding yeast, unique protein Sgs1p plays key regulating mitotic functions S-phase checkpoint response (15, 60). When expressed WRN proteins able partially suppress defects sgs1 mutants (66), suggesting function counterparts evolutionarily conserved. includes slight reduction growth rate, 10-fold increase chromosome missegregation, frequency, high sensitivity methyl methanesulfonate hydroxyurea (HU) 66), consequence increased number extrachromosomal ribosomal circles cell (17, 51, 60, 61). acts redundantly yeast Srs2p, has been shown inhibit loading Rad51p onto single-stranded (ssDNA) vitro (33, 56). In addition, display some meiotic such delayed prophase defective synapsis (16, 45). vitro, interacts physically Top3p (17), Sgs1p-Top3p, suppresses crossovers double-strand (25). type I topoisomerase catalyzes passage two double strands through each other consecutive rejoining cycles, one single time (58). humans, association IIIα observed somatic cells. this corroborated their interaction (26, 64). fission mutations suppressors slow-growth top3 34). It on substrates created Sgs1p. Similarly Sgs1p, involved levels (17). To better understand vivo gene genetic interactions top-3 rad-51 multicellular system, we undertook comprehensive analysis roles Caenorhabditis elegans ortholog RecQ-like helicase. C. provides several advantages study ortholog. animal circumvents intrinsic complications mammalian systems, including disruptions early embryonic lethality or programmed death stages, confound detailed cytological respective (22, 35, 36, 55, 65, 67). Several features adult germ line make it powerful system dissection damage responses. Within gonad organized highly polarized way. distal end ovotestes contains stem compartment followed different stages prophase. dissected cells, pairing, observed. damage, pathways cause cycle arrest apoptotic pachytene (3, 19, 24, 49). The encodes four helicases. Here show HIM-6 (for incidence males) corresponds worm protein. Homozygous him-6 loss-of-function radiation sensitive ionizing radiation-induced response. decrease crossover altered pattern RAD-51 foci, progression recombination. needed maintain and, contrast situation lead catastrophy division Mitotic top-3(RNAi); worms depends rad-51. itself step after initiation