Loss of S1pr1 does not change platelet life span, serum TPO levels, and MK development. (A) Platelet life span assays in the indicated genotypes. n = 3–5 per genotype. (B) Serum TPO levels. n = 3–5 per genotype. (C) Quantification of CFU-MK numbers in FL cells. Data are representative of three independent experiments with triplication. (D) Number of mature MKs in cultured FL cells. Data are representative of four independent experiments with triplication. (E) Representative immunostaining of MKs in mouse femoral BM. MKs were detected by the MK-specific marker CD41 (green). DAPI is stained blue. Bars, 10 µm. (F) Quantification of MK numbers per 20× high-power field in femoral BM. n = 3 mice per genotype. All error bars represent SEM.