Acute Myeloid Leukemia (AML) and myelodysplastic syndrome (MDS) are characterized by increased cell proliferation and a block in differentiation preventing young cells from becoming mature useful blood cells. Transcription factors which govern the development and function of blood cells are frequently mutated in AML. We and others recently found mutations in the transcriptional co-repressor BCOR in AML and MDS. This study will use tissue culture studies and a murine model system to explore the function of BCOR in normal blood cell development and malignant transformation. These studies will broaden our understanding of AML/MDS and may lead to the development of novel therapeutics for these diseases.