Epigenomic Dynamics of Clonal Hematopoiesis

PROJECT SUMMARY The human body constantly replenishes blood and immune cells from stem cells in bone marrow through a differentiation process termed hematopoiesis. Disruptions in this process can lead to hematologic malignancies. Classically, hematopoietic fate decisions were modeled as discrete steps, but recent single-cell RNA sequencing studies demonstrate that hematopoiesis is continuous and that fate restriction occurs even within the hematopoietic stem cell population. These early fate decisions and the prevalence of epigenetic regulator mutations in hematologic malignancies highlight the essential role of the epigenome in hematopoietic fate commitment and the necessity of understanding these mechanisms at a fundamental level. Previous studies have demonstrated that epigenetic priming occurs in hematopoietic stem cells, but techniques capable of measuring these states in single cells have only recently become available. Utilizing single-cell measurements of gene expression, chromatin accessibility, and histone post-translational modifications in healthy hematopoiesis, I will develop computational tools to identify regulatory dynamics of cell fate gain and loss unique to single lineages. To characterize dysregulation of regulatory dynamics in disease, I will knock in a clinically relevant nonsense mutation in ASXL1, a regulator of histone H3 lysine 27 trimethylation, in human hematopoietic stem cells, differentiate them in vitro, and assay gene expression, chromatin accessibility, and multiple histone modifications in single-cell experiments to identify how these regulatory programs are disrupted and where in the developmental trajectory this disruption occurs. This research will unravel the complex regulatory landscape of priming and lineage biases in healthy hematopoiesis and improve the mechanistic understanding of hematologic malignancies in need of improved therapies.