SLX4/HIM-18 is a scaffold protein that interacts with the structure specific endonucleases, SLX1, MUS81-EME1 and XPF-ERCC1 [1,2,3,4,5,6]. These nucleases coordinately cut branched DNA structures such as flaps, replication forks and Holliday junctions [1,2,3,4,5,6,7]. Mutations in SLX4 were found in patients with Fanconi anemia, breast cancer, and leukemia [8,9,10,11]. During meiotic recombination, the final step of crossover formation is thought to be the resolution of Holliday junctions. We previously reported that crossover formation in
him-18 single and
slx-1 mus-81;
xpf-1;
gen-1 quadruple mutants exhibited a 50-70% compared to wild type, resulting in approximately 80% embryonic lethality [6,12]. These results suggested that as of yet unidentified Holliday junction resolvases contribute to the resolution of of the remaining Holliday junctions in the
him-18 and
slx-1 mus-81;
xpf-1;
gen-1 quadruple mutants. To identify new Holliday junction resolvases, we performed an EMS mutagenesis screen in a
him-18 null mutant background in C. elegans. We isolated 11 strains exhibiting >95% maternal effect embryonic lethality (5 of them show 100% embryonic lethality). We are investigating whether these strains exhibit defects in Holliday junction resolution during meiotic recombination by observing the delay of bivalent maturation and measuring crossover frequency. F1 survivors are not fertile in the
him-18 mutant background. Interestingly, we obtained 2 suppressor lines, which can produce fertile animals. The proteins encoded by these genes can be potential drug targets for SLX4/him-18 deficient diseases such as breast cancer, leukemia and Fanconi anemia. We are currently identifying the mutations for both the enhancers and suppressors by whole genome sequencing. The relationship between these mutations and crossover formation will be discussed. [1] Fricke and Brill. Genes Dev. 2003; 17(14):1768-78. [2] Yildiz et al., Mol Cell. 2002; 10(6):1503-9. [3] Munoz et al., Mol Cell. 2009; 35(1):116-27. [4] Fekairi et al., Cell. 2009; 138(1):78-89. [5] Svendsen et al., Cell. 2009; 138(1):63-77. [6] Saito et al., PLoS Genet. 2009; 5(11):
e1000735. [7] Saito et al., PLoS Genet. 2012; 8(8):
e1002888. [8] Stoepker et al., Nat Genet. 2011; 43(2):138-41. [9] Kim et al.,Nat Genet. 2011; 43(2):142-6. [10] Kurian et al., J Clin Oncol. 2014; 32(19):2001-9. [11] Spinella et al.,BMC Cancer. 2015; 15:539. [12] Saito et al., PLoS Genet. 9(7):
e1003586.