Extended Data Figure 1: BM MSC reduction in compound mutant mice and recipients of mutant haematopoietic cells is not due to cell differentiation.

a, b, Blood counts of Nes-gfp;Mx1-cre;JAK2(V617F) and control mice 4-8 weeks after pIpC treatment (a) and Nes-gfp mice 10-12 weeks after transplantation with BM cells from MPN and control mice (b). Note the similar erythrocytosis, neutrophilia and thrombocytosis in compound mutant mice and Nes-gfp mice transplanted with mutant cells. Each dot represents a mouse. c, GFP fluorescence in skull BM of Nes-gfp mice 6–8 weeks after transplantation with MPN and control BM cells (n = 8; scale bar, 100 µm). d, Frequency of CD45⁻CD31⁻Ter119⁻Nes-GFP⁺ BM cells in MPN (n = 9) and control (n = 7) mice 6–8 weeks after pIpC induction. e, Giemsa-stained fibroblastic colony-forming units (CFU-F) from immunomagnetically-enriched BM CD45⁻Ter119⁻ cells 30 weeks after transplantation with MPN and control BM cells. f, FACS analyses of BM CD45⁻CD31⁻Ter119⁻ cells from MPN and control mice 8 weeks after pIpC treatment (n = 3). The specified MSC markers were used. Mean ± s.e.m. g, BM reticulin staining; MPN mice showed incipient fibrosis (arrow) 6 weeks after pIpC treatment (magnification, ×200). h, i, Lineage-tracing studies of BM nestin⁺ cells in MPN. h, Experimental design. Nes-cre^ERT2;RCE:loxP mice were transplanted with MPN and control BM cells and fed with tamoxifen diet. Disease development was monitored over 28 weeks. i, Blood counts showing progressive neutrophilia and thrombocytosis in recipients of MPN BM cells (n = 3). j, Femoral haematoxylin and eosin stainings showing abnormal bone formation in recipients of MPN BM cells (magnification, ×100). *P < 0.05, **P < 0.01, ***P < 0.001 (unpaired two-tailed t test).