Clonal analysis of lineage fate in native haematopoiesis

Abstract

SUMMARY Hematopoiesis, the process of mature blood and immune cell production, is functionally organized as a hierarchy, with self-renewing hematopoietic stem cells (HSCs) and multipotent progenitor (MPP) cells sitting at the very top1,2. Multiple models have been proposed as to what the earliest lineage choices are in these primitive hematopoietic compartments, the cellular intermediates, and the resulting lineage trees that emerge from them3–10. Given that the bulk of studies addressing lineage outcomes have been performed in the context of hematopoietic transplantation, current lineage branching models are more likely to represent roadmaps of lineage potential rather than native fate. Here, we utilize transposon (Tn) tagging to clonally trace the fates of progenitors and stem cells in unperturbed hematopoiesis. Our results describe a distinct clonal roadmap in which the megakaryocyte (Mk) lineage arises largely independently of other hematopoietic fates. Our data, combined with single cell RNAseq, identify a functional hierarchy of uni- and oligolineage producing clones within the MPP population. Finally, our results demonstrate that traditionally defined long-term HSCs (LT-HSCs) are a significant source of Mk-restricted progenitors, suggesting that the Mk-lineage is the predominant native fate of LT-HSCs. Our study provides evidence for a substantially revised roadmap for unperturbed hematopoiesis, and highlights unique properties of MPPs and HSCs in situ.

Lineage tracing of murine adult hematopoietic stem cells reveals active contribution to steady-state hematopoiesis

“…The HPC2 population was not investigated in previous reports, 16,17,20 and labeling of platelets by HSCs were not traced in the studies by Sun et al and Busch et al Recently, it was reported that the megakaryocyte lineage is the predominant fate of HSCs in the native state. 33 Interestingly, HSCs have been shown to produce HPC2/MPP2 after brief in vitro culture without appreciable production of MPPs (termed ST-HSCs in Pietras et al 30 ). Therefore, it is tempting to speculate that the hierarchical order of hematopoiesis is different during native hematopoiesis than after transplantation, but further work is needed to decipher the hierarchical organization of hematopoiesis in the native state.…”

Concise Review: Bipotent Megakaryocytic-Erythroid Progenitors: Concepts and Controversies

“…[37] In a subsequent study, this strategy revealed that half of the Mk lineage appeared to be produced independently from other lineages by the HSC compartment. [38] However, the authors suggested that the MEP stage could be too transient to be detected by their approach. [38]…”

“…[38] However, the authors suggested that the MEP stage could be too transient to be detected by their approach. [38]…”

Metabolism as master of hematopoietic stem cell fate

“…Fluorescence-activated cell sorting (or FACS) greatly facilitated the purification of transplantable HSCs through positive and negative selection, as described in pioneering publications (e.g., [8] from Dr. Irving Weissman’s group). HSCs are widely believed essential to hematopoiesis under recovery or other stress conditions [9–13], and HSC transplantation has, therefore, been a key therapeutic strategy in combatting hematological disorders [14, 15]. Intriguingly, recent advances utilizing single-cell approaches have revealed at the apex of hematopoiesis a rare population of HSCs that can sustain all the hematopoietic lineages throughout the lifetime of the individual, and may be critical to the rapid hematopoietic response required by acute conditions.…”