RESEARCH SUMMARY Hematopoiesis is now recognized as the integrated activity of multiple, largely progenitor clones with heterogeneous behavior. Clonal complexity is thought to diminish with age and human studies suggest that oligoclonal hematopoiesis with disease associated mutations is common. The presence of such clones incurs a substantial risk of hematologic neoplasia and all cause mortality. The overall goal of this proposal is to understand the molecular drivers of clonal behavior under stress conditions and to test whether modifying those drivers is capable of changing the relative competitive balance of normal and abnormal, risk bearing clones in animal models. We will use techniques of fluouresence clonal tracking in the mouse developed by us and compare these with retrotransposon clonal marking techniques in the mouse of Carmago and fluorescence clonal tracking techniques in the zebrafish developed by Zon. Further, we will characterize genetic characteristics of clones at single cell resolution using techniques of Tenen and define ncRNA candidate molecular drivers with Tenen. Finally, we will target epigenetic modifiers defined by Orkin, Tenen and Zon to test the impact on clonal competition between normal and mutant clones in vivo. Combined these complementary and collaborative approaches will point to methods for altering competitive relationships in hematopoiesis in favor of normal cells.