Neutrophils are increasingly recognized as key players in the tumor immune response and are associated with poor clinical outcomes. Despite recent advances characterizing the diversity of neutrophil states in cancer, common trajectories and mechanisms governing the ontogeny and relationship between these neutrophil states remain undefined. Here, we demonstrate that immature and mature neutrophils that enter tumors undergo irreversible epigenetic, transcriptional, and proteomic modifications to converge into a distinct, terminally differentiated dcTRAIL-R1 ⁺ state. Reprogrammed dcTRAIL-R1 ⁺ neutrophils predominantly localize to a glycolytic and hypoxic niche at the tumor core and exert pro-angiogenic function that favors tumor growth. We found similar trajectories in neutrophils across multiple tumor types and in humans, suggesting that targeting this program may provide a means of enhancing certain cancer immunotherapies.

Ever since hematopoietic stem cells (HSCs) were first identified half a century ago, their differentiation roadmap has been extensively studied. The classical model of hematopoiesis has long held as a dogma that HSCs reside at the top of a hierarchy in which HSCs possess self-renewal capacity and can progressively give rise to all blood lineage cells. However, over the past several years, with advances in single cell technologies, this developmental scheme has been challenged. In this review, we discuss the evidence supporting heterogeneity within HSC and progenitor populations as well as the hierarchical models revised by novel approaches mainly in mouse system. These evolving views provide further understanding of hematopoiesis and highlight the complexity of hematopoietic differentiation.

Emerging evidence has revealed a direct differentiation route from hematopoietic stem cells to megakaryocytes (direct route), in addition to the classical differentiation route through a series of restricted hematopoietic progenitors (stepwise route). This raises the question of the importance of two alternative routes for megakaryopoiesis. Here, we developed fate-mapping systems to distinguish the two routes, comparing their quantitative and functional outputs. We found that megakaryocytes were produced through the two routes with comparable kinetics and quantity under homeostasis. Single-cell RNA sequencing of the fate-mapped megakaryocytes revealed that the direct and stepwise routes contributed to the niche-supporting and immune megakaryocytes, respectively, but contributed to the platelet-producing megakaryocytes together. Megakaryocytes derived from the two routes displayed different activities and were differentially regulated by chemotherapy and inflammation. Our work links differentiation route to the heterogeneity of megakaryocytes. Alternative differentiation routes result in variable combinations of functionally distinct megakaryocyte subpopulations poised for different physiological demands.

Spatiotemporal chromatin reorganization during hematopoietic differentiation has not been comprehensively characterized, mainly because of the large numbers of starting cells required for current chromatin conformation capture approaches. Here, we introduce a low-input tagmentation-based Hi-C (tagHi-C) method to capture the chromatin structures of hundreds of cells. Using tagHi-C, we are able to map the spatiotemporal dynamics of chromatin structure in ten primary hematopoietic stem, progenitor, and differentiated cell populations from mouse bone marrow. Our results reveal that changes in compartment dynamics and the Rabl configuration occur during hematopoietic cell differentiation. We identify gene-body-associating domains (GADs) as general structures for highly expressed genes. Moreover, we extend the body of knowledge regarding genes influenced by genome-wide association study (GWAS) loci through spatial chromatin looping. Our study provides the tagHi-C method for studying the three-dimensional (3D) genome of a small number of cells and maps the comprehensive 3D chromatin landscape of bone marrow hematopoietic cells.

Adenosine-to-inosine RNA editing and the catalyzing enzyme adenosine deaminase are both essential for hematopoietic development and differentiation. However, the RNA editome during hematopoiesis and the underlying mechanisms are poorly defined. Here, we sorted 12 murine adult hematopoietic cell populations at different stages and identified 30 796 editing sites through RNA sequencing. The dynamic landscape of the RNA editome comprises stage- and group-specific and stable editing patterns, but undergoes significant changes during lineage commitment. Notably, we found that antizyme inhibitor 1 (Azin1) was highly edited in hematopoietic stem and progenitor cells (HSPCs). Azin1 editing results in an amino acid change to induce Azin1 protein (AZI) translocation to the nucleus, enhanced AZI binding affinity for DEAD box polypeptide 1 to alter the chromatin distribution of the latter, and altered expression of multiple hematopoietic regulators that ultimately promote HSPC differentiation. Our findings have delineated an essential role for Azin1 RNA editing in hematopoietic cells, and our data set is a valuable resource for studying RNA editing on a more general basis.