PROJECT SUMMARY Since 2002 when my laboratory discovered GATA1 mutations in all cases acute megakaryocytic leukemia in children with Down syndrome, I have been at the forefront of defining the specific genetic events that promote leukemia. I have extensively studied the role of GATA1 in normal and malignant hematopoiesis and gained many insights into the contributions of several chromosome 21 genes, including DYRK1A, ERG and CHAF1B, in leukemia. My laboratory is also well established in the field of the myeloproliferative neoplasms (MPNs), especially in the role of megakaryocytes in the pathogenesis of myelofibrosis and the development of new therapies for this disease. In this R35 application, I propose to focus my laboratory over the next 7 years (and beyond) on understanding the mechanisms of leukemia progression from clonal hematopoietic disorders. Specifically, we will identify and compare the ways that pediatric and adult disorders progress to acute myeloid leukemia. We will leverage large scale CRISPR/Cas9 screening, animal models and primary patient samples to deeply characterize the mechanisms of transformation and focus on answering three questions: 1) What are the similar and disparate events that promote malignant progression of pediatric versus adult blood disorders? 2) How does dysregulation of pathways downstream of identified tumor suppressor genes promote malignant progression? 3) Which investigational or approved therapies can prevent progression or treat the tumors? The answers to these questions will increase our basic understanding of cancer, reveal new therapeutic targets and possibly shed light on chemoprevention strategies.