Enter the text here that is the new abstract information for your application. This section must be no longer than 30 lines of text. Evaluating the extent and dynamics of epigenetic heterogeneity in blood stem cells at the single-cell level Proper control of hematopoietic stem cell (HSC) self-renewal and differentiation is essential for all humans, not only during healthy conditions, but also for the treatment of various hematological disorders through bone marrow transplantations. Understanding the mechanisms of hematopoiesis is therefore vital for understanding healthy physiology and for creating efficient and rational approaches for blood cell regeneration therapies. Intriguingly, prior research has reported substantial heterogeneity in the distributions of final cell fates for the descendants of individual HSCs, even for clonally related cells in identical environments. These differences in lineage potential could result from differences in epigenetic state, however, the study of epigenetic states at the level of individual stem cells has been hindered by limitations in available methodology. To overcome these limitations, we have developed a new microscopy-based assay called SCEPTRE (Single-Cell Evaluation of Post-TRanslational Epigenetic encoding) that can sensitively resolve epigenetic states at single gene loci in single cells (Woodworth et al. 2021). In Aim 1 we will use SCEPTRE to study histone post-translational modifications in HSCs at key gene loci governing lymphomyeloid differentiation. In Aim 2, toward the goal of analyzing epigenetic state dynamics, we will develop a live imaging assay for tracking HSC clones over multiple cell generations that we will then combine with SCEPTRE to probe epigenetic heritance at the clonal level. If successful, this work will open the door for future studies that clarify the origins and consequences of heterogeneity in HSC biology.