Megakaryocytes and platelet production. (A) Cross-sectioned femurs harvested from WT, RGS18^−/−, RGS10^−/−, and RGS10^−/−18^−/− mice were stained for CD41 (α_IIb integrin) and counterstained with hematoxylin. Large, multinucleate CD41⁺ cells were counted as megakaryocytes. White arrows point to representative examples. (B) Megakaryocyte counts from 5 randomly selected fields per mouse. n = 3; mean ± SEM. (C) Platelet depletion with an anti-GPIbα antibody followed by recovery over the course of 96 hours represented as a percentage of the baseline for each genotype. **P ≤ .05 for WT vs RGS18^−/− and RGS10^−/−18^−/−. n = 6; mean ± SEM.