Disruption of mouse Slx4, a regulator of structure-specific nucleases, phenocopies Fanconi anemia

The evolutionarily conserved SLX4 protein, a key regulator of nucleases, is critical for DNA damage response. SLX4 nuclease complexes mediate repair during replication and can also resolve Holliday junctions formed during homologous recombination. Here we describe the phenotype of the Btbd12 knockout mouse, the mouse ortholog of SLX4, which recapitulates many key features of the human genetic illness Fanconi anemia. Btbd12-deficient animals are born at sub-Mendelian ratios, have greatly reduced fertility, are developmentally compromised and are prone to blood cytopenias. Btbd12(-/-) cells prematurely senesce, spontaneously accumulate damaged chromosomes and are particularly sensitive to DNA crosslinking agents. Genetic complementation reveals a crucial requirement for Btbd12 (also known as Slx4) to interact with the structure-specific endonuclease Xpf-Ercc1 to promote crosslink repair. The Btbd12 knockout mouse therefore establishes a disease model for Fanconi anemia and genetically links a regulator of nuclease incision complexes to the Fanconi anemia DNA crosslink repair pathway.     

Fancd2 counteracts the toxic effects of naturally produced aldehydes in mice

Reactive aldehydes are common carcinogens. They are also by-products of several metabolic pathways and, without enzymatic catabolism, may accumulate and cause DNA damage. Ethanol, which is metabolised to acetaldehyde, is both carcinogenic and teratogenic in humans. Here we find that the Fanconi anaemia DNA repair pathway counteracts acetaldehyde-induced genotoxicity in mice. Our results show that the acetaldehyde-catabolising enzyme Aldh2 is essential for the development of Fancd2(-/-) embryos. Nevertheless, acetaldehyde-catabolism-competent mothers (Aldh2(+/-)) can support the development of double-mutant (Aldh2(-/-)Fancd2(-/-)) mice. However, these embryos are unusually sensitive to ethanol exposure in utero, and ethanol consumption by postnatal double-deficient mice rapidly precipitates bone marrow failure. Lastly, Aldh2(-/-)Fancd2(-/-) mice spontaneously develop acute leukaemia. Acetaldehyde-mediated DNA damage may critically contribute to the genesis of fetal alcohol syndrome in fetuses, as well as to abnormal development, haematopoietic failure and cancer predisposition in Fanconi anaemia patients.     

Insertional mutagenesis identifies multiple networks of cooperating genes driving intestinal tumorigenesis

The evolution of colorectal cancer suggests the involvement of many genes. To identify new drivers of intestinal cancer, we performed insertional mutagenesis using the Sleeping Beauty transposon system in mice carrying germline or somatic Apc mutations. By analyzing common insertion sites (CISs) isolated from 446 tumors, we identified many hundreds of candidate cancer drivers. Comparison to human data sets suggested that 234 CIS-targeted genes are also dysregulated in human colorectal cancers. In addition, we found 183 CIS-containing genes that are candidate Wnt targets and showed that 20 CISs-containing genes are newly discovered modifiers of canonical Wnt signaling. We also identified mutations associated with a subset of tumors containing an expanded number of Paneth cells, a hallmark of deregulated Wnt signaling, and genes associated with more severe dysplasia included those encoding members of the FGF signaling cascade. Some 70 genes had co-occurrence of CIS pairs, clustering into 38 sub-networks that may regulate tumor development.