Lin- PU.1dim GATA-1- defines haematopoietic stem cells with long-term multilineage reconstitution activity.

Despite extensive characterization of the state and function of haematopoietic stem cells (HSCs), the use of transcription factors to define the HSC population is still limited. We show here that the HSC population in mouse bone marrow can be defined by the distinct expression levels of Spi1 and Gata1. By using a double fluorescence knock-in mouse model, PGdKI, in which the expression levels of PU.1 and GATA-1 are indicated by the expression of GFP and mCherry, respectively, we uncover that the HSCs with lymphoid and myeloid repopulating activity are specifically enriched in a Lin- PU.1dim GATA-1- (LPG) cell subset. In vivo competitive repopulation assays demonstrate that bone marrow cells gated by LPG exhibit haematopoietic reconstitution activity which is comparable to that of classical Lin- Sca1+ c-kit+ (LSK). The integrated analysis of single-cell RNA sequence data from LPG and LSK-gated cells reveals that a transcriptional network governed by core TFs contributes to regulation of HSC multipotency. These discoveries provide new clues for HSC characterization and functional study.

A novel inducible haematopoietic cell-depleting mouse model for chimeric complementation of blood cells.

Haematopoietic stem cell transplantation (HSCT) is widely used in regenerative medicine. HSCT can be used not only to treat certain types of blood cancer and immune disorders but also to induce immune tolerance in organ transplantation. However, the inadequacy of HSCs available for transplantation is still a major hurdle for clinical applications. Here, we established a novel inducible haematopoietic cell-depleting mouse model and tested the feasibility of using chimeric complementation to regenerate HSCs and their progeny cells. Large populations of syngeneic and major histocompatibility-mismatched haematopoietic cells were successfully regenerated by this model. The stable allogeneic chimeric mice maintained a substantial population of donor HSCs and Tregs, which indicated that the donor allogeneic HSCs successfully repopulated the recipient blood system, and the regenerated donor Tregs played essential roles in establishing immune tolerance in the allogeneic recipients. In addition, rat blood cells were detected in this model after xenotransplantation of rat whole bone marrow (BM) or Lin- BM cells. This mouse model holds promise for regenerating xenogeneic blood cells, including human haematopoietic cells.