Increased frequency of CD41 expressing Mk-biased HSCs in mutant JAK2-expressing mice. (A) Frequencies (left) and percentages (right) of CD41^hi and CD41^lo HSCs within the phenotypic HSC compartment in BM in the indicated genotypes (n = 7 mice per genotype). Frequencies (left) and percentages (right) of CD41^hi and CD41^lo HSCs in the phenotypic HSC compartment in the spleen of the indicated genotype (n = 7 mice per genotype). (B) Analysis of colonies grown from a FACS-sorted single CD41^hi or CD41^lo HSC in liquid culture showing the percentages of colonies containing Mk (CD41⁺), myeloid (CD16⁺), or mixed (Mk and myeloid, CD41⁺/CD16⁺) cells after 10 days of culture. We plated 48 single HSCs per mouse with 3 mice per genotype in 384-well plates (ie, a total of 144 single cells per genotype) and scored each well separately after 10 days of culture. (C) Setup of transplantations with purified CD41^hi and CD41^lo HSC subsets into lethally irradiated recipients (n = 6 mice per cell type and genotype). Data show peripheral blood counts in recipients of CD41^hi or CD41^lo HSCs (top row) and donor chimerism determined as a percentage of GFP⁺ cells in PB (bottom row). Spleen weights of CD41^hi and CD41^lo HSC transplant-recipient mice at 24 weeks after transplantation are shown (top right graph). Group size: n = 6 mice per cell type and genotype. (D) Analysis of donor chimerism (percentage of GFP⁺ cells) in progenitor and stem cells in BM and spleen in CD41^hi and CD41^lo HSC transplant recipients at 24 weeks after transplantation (n = 6 mice per cell type and genotype). (E) Analysis of recipients of CD41^lo HSC transplants. Stacked bar graph shows percentages of CD41^lo and CD41^hi HSCs in the GFP⁺ subset of LT-HSCs. One- or 2-way analyses of variance followed by Tukey’s multiple-comparisons test were used for multiple-group comparisons. All data are means ± standard error of the mean. *P < .05; **P < .01; ***P < .001; ****P < .0001.