Determinants of epigenetic inheritance in human stem cell fate decisions

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Project summary In hematopoietic stem cells (HSCs), the epigenome confers self-renewal and differentiation functions wherein inheritance of HSC chromatin states is persistent across cell cycles. My postdoctoral studies focused on a fundamental epigenetic feature involving the local recycling of pre-existing, parental nucleosomes, which showed that repressed, but not active, chromatin domains are inherited across DNA replication. While identifying the histone chaperone(s) that facilitate the inheritance of repressed chromatin domains in mouse embryonic stem cells, I discovered that nucleophosmin, NPM1, plays an essential role in this process. NPM1 is a histone chaperone whose genetic mutation and rearrangement are found in ~30% of all adult AML, however its function in normal hematopoiesis remains unknown. Furthermore, key questions persist on the inheritance of H3K27me chromatin domains, such as what brings NPM1 and the polycomb repressive complex 2 (PRC2) to the DNA replication fork during S-phase, how are polycomb chromatin domains inherited in the developing immune system, and whether parental nucleosome segregation has a role in the precise balancing between self-renewal and differentiation capacities that shape a hematopoietic cascade. In this proposal, my group will identify the molecular basis for constructing the heritable human epigenome of HSCs and discover the chromatin dynamics that provide HSCs the ability to both self-renew and differentiate. We will use in vitro human induced pluripotent stem cells and differentiate them to derive a hematopoietic progenitor cell fate. Using this system, we will conduct cutting age genome engineering, proteomics, and imaging technologies to discover the function of histone chaperones and polycomb in constructing the heritable epigenome of HSCs.