BMMCs contain much more subpopulations and are more active (Extended Data Fig. 1g-1j).
HSPCs form a single connected entity on tSNE projectionDue to the limited number of HSPCs in BMMCs (Fig. 1b), CD34+ cells, representing HSPCs, were enriched by fluorescence-activated cell sorting (FACS) for investigating hematopoiesis (Extended Data Fig. 2a). The HSPCs essentially formed a single connected entity extending in several directions on tSNE projection and were clustered into 27 clusters for better understanding of the hematopoietic process ( Fig. 1e). We inferred the cell type of each cluster by checking the expression of hematopoietic lineage specific genes ( Fig. 1e, Extended Data Fig. 2b), such as HSC (EMCN+, THY1+, MEG3+, HES1+, Lin-; cluster 1), megakaryocytic progenitors (MkP) (PF4+, GP9+; clusters 5, 7), early erythroid progenitors (EEP) (APOE+, CD36+, CA1+; clusters 8-11), neutrophil, monocyte and DC progenitors (CSF3R+, MPO+ and LYZ+; clusters 13-20) (Fig. 1f, Extended Data Fig. 2b), lymphoid progenitors (CD79A+, IGHM+, VPREB1+; clusters 21-27) ( Fig. 1F and
Extended Data Fig. 2b)Cluster 12 highly expressed mast cell and basophil specific genes including HDC, TPSAB1 and MS4A2, as well as eosinophil specific genes including PRG2 and CPA3 ( Fig. 1f and Extended Data Fig. 2b), which could be recently reported Basophil/Eosinophil/Mast progenitors (Ba/Eo/MaP) 10,16 . We did not detect any cluster with gene expression patterns similar to common myeloid progenitor (CMP) (CD34+, CD38+, CD123+, CD45RA-, CD10-and Lin-), consistent with recent studies showing that CMP is a heterogeneous mixture of erythroid and myeloid primed progenitors 10,17,18 . Moreover, we observed multiple subpopulations within pre-defined MkP, EEP, GMP, Pro-B II and so on (Fig. 1e).The expression levels of many genes are gradually changing along the three EEP populations, among which the expression levels of HBA1, TFRC, GYPA, ALAS2, PLK1 and MKI67 gradually increased as the distance to HSC increase (Extended Data Fig. 2b, 2i, 2j). Overall, HSPCs contain a substantial higher fraction of cells in active cell cycles and cell states than that of other BMMCs (Extended Data Fig. 2c-2h). Interestingly, major early stem and progenitor cells (HSC, MPP, LMPP) are in resting phase while major later progenitors are in active proliferation (Extended Data Fig. 2e, 2f), potentially indicating the early progenitor constitutes the major cell pool for regulating hematopoiesis while later progenitors are in simple transitional states.
Continuous hematopoietic lineages with hierarchical structureWe implemented Slingshot 19 and SPRING 20 on HSPCs to conduct pseudo-time inference.Pseudo-time ordering of HSPCs exhibits a tree-like structure in which HSC forms the root, from which seven lineages gradually emerged with a hierarchical structure ( Fig. 2a, 2b, 2c), essentially consistent with the cell lineages base on PCA projection (Extended Data Fig. 3a). The results are consistent with recent reports that hematopoiesis is a continuous process 8-10 , but with...