FVIIIKO and PAR1 KO mice exhibit impaired interaction between stroma cells and hematopoietic niche. (A) A scheme depicting the procedure in the assay used to distinguish between the roles of PAR1 on stromal cells vs PAR1 on HSCs. Host mice were lethally irradiated by split-dose total body irradiation (total of 10 Gy on day 3 and 4 Gy on day 1) and transplanted (day 0) with 5 × 10⁶ donor cells. One month later, mice were mobilized by G-CSF for 7 days. (B) Spleen weight was examined for the 3 different chimeras tested as indicated. Bars represent average values ± SD.