Stem cell phenotype of HSCs from Thpo^−/− mice is reversible. (A) PB platelet count fold change in Thpo^+/+, Thpo^−/−, Thpo^+/+ Ro, and Thpo^−/− Ro mice (n > 5). (B) Fold change in HSC number in BM (2 femurs and 2 tibias) of Thpo^+/+, Thpo^−/− with romiplostim treatment. (C) Representative flow cytometric plot of cell cycle analysis Thpo^+/+ Ro and Thpo^−/− Ro HSCs and percentage of HSCs in the G₀ stage in Thpo^+/+, Thpo^−/−, Thpo^+/+ Ro, and Thpo^−/− Ro HSCs. (D-F) Primary competitive BM transplantation of 500 HSCs isolated from Thpo^+/+, Thpo^−/−, Thpo^+/+ Ro, or Thpo^−/− Ro mice (n = 5). (D) PB chimerism of total mononuclear cells. (E) PB chimerism of GM cells (Mac1⁺ Gr1⁺), B cells (B220⁺), and T cells (CD4⁺ CD8⁺). (F) BM chimerism of HSCs (Lin⁻ cKit⁺ Sca1⁺ CD48^- CD150⁺ CD34⁻). (G-I) Secondary competitive BM transplantation of 2 × 10⁶ BM mononuclear cells isolated from recipients of primary BM transplantation. (G) PB chimerism of total mononuclear cells (n = 5). (H) PB chimerism of GM cells, B cells, and T cells (n = 5). (I) BM chimerism of HSCs (n = 5). *P < .05, **P < .01, Student t test (A-B), Fisher’s least significant difference test (C), Tukey test (D-I).