Neogenin-1 distinguishes between myeloid-biased and balanced Hoxb5+ mouse long-term hematopoietic stem cells

Hematopoietic stem cells (HSCs) self-renew and generate all blood cells. Recent studies with single-cell transplants and lineage tracing suggest that adult HSCs are diverse in their reconstitution and lineage potentials. However, prospective isolation of these subpopulations has remained challenging. Here, we identify Neogenin-1 (NEO1) as a unique surface marker on a fraction of mouse HSCs labeled with Hoxb5, a specific reporter of long-term HSCs (LT-HSCs). We show that NEO1+Hoxb5+ LT-HSCs expand with age and respond to myeloablative stress in young mice, while NEO1–Hoxb5+ LT-HSCs exhibit no significant change in number. Furthermore, NEO1+Hoxb5+ LT-HSCs are more often in the G2/S cell cycle phase compared to NEO1–Hoxb5+ LT-HSCs in both young and old bone marrow. Upon serial transplantation, NEO1+Hoxb5+ LT-HSCs exhibit myeloid-biased differentiation and reduced reconstitution, while NEO1–Hoxb5+ LT-HSCs are lineage-balanced and stably reconstitute recipients. Gene expression analysis reveals erythroid and myeloid priming in the NEO1+ fraction and association of quiescence and self-renewal-related transcription factors with NEO1− LT-HSCs. Finally, transplanted NEO1+Hoxb5+ LT-HSCs rarely generate NEO1–Hoxb5+ LT-HSCs, while NEO1–Hoxb5+ LT-HSCs repopulate both LT-HSC fractions. This supports a model in which dormant, balanced, NEO1–Hoxb5+ LT-HSCs can hierarchically precede active, myeloid-biased NEO1+Hoxb5+ LT-HSCs. Bulk RNA-sequencing profiles of NEO1+Hoxb5+ (n = 5) and NEO1–Hoxb5+ (n = 5) LT-HSCs from the bone marrow of 2- to 3-month-old Hoxb5­-mCherry mice.