The new clt-2 mutant and its interaction with FA/BRC recombination pathway in C. elegans

Fanconi Anaemia (FA) is a cancer predisposition syndrome, also inducing sterility and developmental defects. FA associated gene products were found to be involved in a common pathway, to interact with DNA damage response proteins, such as BRCA1, RAD-51, ATM, and to support homologous recombination. FA cells are hypersensitive to interstrand cross linking (ICL) agents. Genes in the FA/BRC pathway are evolutionary conserved, allowing mechanistic studies in the model system C. elegans [1,2]. The FA pathway is involved in the choice between the high fidelity repair pathway, Homologous-Repair (HR), and the error prone Non-Homologous-End-Joining (NHEJ). Studies in C. elegans, in fact, have demonstrated that FCD-2 (FANCD2 orthologue) suppresses the improper use of NHEJ pathway preventing DNA repair errors and developmental defects in mutant worms. The clt-2 mutant was originally isolated in a screening for suppressors of the inter-strand cross-linking (ICL) hypersensitivity of the fcd-2 mutant. The mutation is not a fcd-2 back-mutation because unlike fcd-2 it maps on the left arm of the II chromosome. Further characterization has shown that the clt-2 mutant rescues most of the fcd-2 meiotic and developmental defects and the double mutant behaves as a wild type. The clt-2 mutation, in a fcd-2 background, restores the NHEJ down-regulation during meiosis and early embryogenesis, although, it does not affect NHEJ after DNA damages in late embryogenesis. The expression of NHEJ genes does not seem to be affected. Developmental defects, observed in fcd-2, disappear in the double mutant. Similarly, clt-2; fcd-2 does not display evident DNA repair delays in gametogenesis nor apoptosis increase. However, the single clt-2 mutant shows a distinct phenotype (including low brood-size and occurrence of developmental defects) not observed in the clt-2; fcd-2 double mutant. Therefore it is the specific interaction of the two mutations in the two genes that leads to the healthy phenotype. 1. Adamo A, Collis SJ, Adelman CA, Silva N, Horejsi Z, Ward JD, Martinez-Perez E, Boulton SJ, La Volpe A. Preventing nonhomologous end joining suppresses DNA repair defects of Fanconi anemia. Mol Cell. 2010 Jul 9;39(1):25-35 2. Adamo A, Montemauri P, Silva N, Ward JD, Boulton SJ, La Volpe A. BRC-1 acts in the inter-sister pathway of meiotic double-strand break repair. EMBO Rep. 2008 Mar;9(3):287-92.