Enhanced stress erythropoiesis in ROCK1^−/− mice is cell autonomous. PHZ was administered intraperitoneally (80 mg/kg) to WT recipient mice transplanted with WT or ROCK1^−/− BM. Recipient mice were harvested 4 days after PHZ injection, PB (20 μL/mouse) was collected from the tail vein in an EDTA-coated capillary tube from recipient mice. (A) Bar graph represents the mean value ± SD of RBCs (M/μL) in each genotype (n = 3 mice per genotype, *P < .05). (B) Bar graph represents the mean value ± SD of HCT (%) in each genotype (n = 3 mice per genotype, *P < .05). (C) Bar graph represents the mean value ± SD of Hb (g/dL), in each genotype (n = 3 mice per genotype, *P < .05). (D) BM was harvested from transplanted mice 4 days after PHZ treatment. Whole BM cells were washed and resuspended in prewarmed PBS and loaded with 10μM 5-(and 6-)-chloromethyl-2′,7′-dichlorodihydrofluorescein diacetate (CM-H₂DCFDA) in the dark for 30 minutes at 37°C. Bar graph representing the mean ± SEM of ROS levels in the WT and ROCK1^−/− erythrocytes (n = 3 mice for each genotype, *P < .05). (E) Bar graph represents the mean ± SEM of Ter119/CD71-positive cells in the BM of WT and ROCK1^−/− BM recipient mice after PHZ injection. (F) Spleen was harvested from transplanted mice 4 days after PHZ treatment. Splenocytes were washed and resuspended in prewarmed PBS and loaded with 10μM CM-H₂DCFDA in the dark for 30 minutes at 37°C. Bar graph represents the mean ± SEM of ROS levels in the WT and ROCK1^−/− BM recipient mice (n = 3 mice for each genotype, *P < .05). (G) Bar graph representing the mean ± SEM of Ter119/CD71 double-positive cells in the spleen of WT and ROCK1^−/− recipient mice after PHZ injection (n = 3 mice for each genotype, *P < .05).