U2AF1 and myelodysplastic syndrome: Conditional knock-in murine models of the common SF mutations (Sf3b1-K700E, Srsf2-P95H, U2af1-S34F) all display some features of MDS, including a macrocytic anemia, with a more pronounced MDS phenotype observed in transplantation experiments using the murine SF-mutant bone marrow cells.17