Reduced numbers and impaired function of hematopoietic stem and progenitor cells in JAK2^V617F mice. (A-B) Representative FACS plots and histograms summarizing the frequencies of LSK and progenitor cells (lineage⁻Sca-1⁻c-Kit⁺), common myeloid progenitors (lineage⁻c-Kit⁺CD34⁺FcγR⁻), megakaryocyte-erythroid progenitor (lineage⁻c-Kit⁺CD34⁻FcγR⁻), and granulocyte-monocyte progenitor (lineage⁻c-Kit⁺CD34⁺FcγR⁺) at 6 and 26 weeks after pIpC. (C) BM cells from JAK2^V617F mice display reduced repopulating capacity in competitive BM transplantation analysis. BM cells from 2 individual donors (6 weeks after pIpC) for each test genotype (ie, JAK2^V617F or JAK2^wt littermate controls) were injected into recipients F1 C57Bl6/129SvEvBrd (CD45.1/CD45.2). Histograms show the proportion of peripheral blood-nucleated cells derived from test cells (CD45.2⁺) compared with repopulation from total donor cells (ie, test plus competitor; CD45.2⁺ plus CD45.1⁺). (D) Marked HSC repopulation defect in secondary transplantation recipients. BM cells from primary transplantation recipients were injected into secondary recipients F1 C57Bl6/129SvEvBrd (CD45.1/CD45.2), which were analyzed 4 and 16 weeks after transplantation. Histograms represent the proportion of peripheral blood nucleated cells derived from the test cells (CD45.2⁺) compared with repopulation from the test plus competitor cells (CD45.2⁺ plus CD45.1⁺). *P < .05. **P < .01. ***P < .001.