Impaired hematopoiesis and leukemia development in mice with a conditional knock-in allele of a mutant splicing factor gene .

Mutations affecting the spliceosomal protein U2AF1 are commonly found in myelodysplastic syndromes (MDS) and secondary acute myeloid leukemia (sAML). We have generated mice that carry Cre-dependent knock-in alleles of (S34F), the murine version of the most common mutant allele of encountered in human cancers. Cre-mediated recombination in murine hematopoietic lineages caused changes in RNA splicing, as well as multilineage cytopenia, macrocytic anemia, decreased hematopoietic stem and progenitor cells, low-grade dysplasias, and impaired transplantability, but without lifespan shortening or leukemia development. In an attempt to identify (S34F)-cooperating changes that promote leukemogenesis, we combined (S34F) with deficiency in mice and further treated the mice with a mutagen, -ethyl--nitrosourea (ENU). Overall, 3 of 16 ENU-treated compound transgenic mice developed AML. However, AML did not arise in mice with other genotypes or without ENU treatment. Sequencing DNA from the three AMLs revealed somatic mutations homologous to those considered to be drivers of human AML, including predicted loss- or gain-of-function mutations in , , , and However, the engineered (S34F) missense mutation reverted to WT in two of the three AML cases, implying that (S34F) is dispensable, or even selected against, once leukemia is established.