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.