Characterization of the Vps33b^fl/fl-ER^T2 mice. (A) Analysis of Vps33b messenger RNA in BM-derived MKs of Vps33b^fl/fl and Vps33b^fl/fl-ER^T2 mice. (B) Spleen to body weight ratio was analyzed in 11-week-old mice 5 weeks post-induction (n = 12 to 16 mice per genotype). (C) Extramedullary hematopoiesis in Vps33b^fl/fl-ER^T2 mice. Representative images of hematoxylin and eosin-stained spleen (top panels) and femur BM (bottom panels) sections from littermate controls (left top and bottom panels) and Vps33b^fl/fl-ER^T2 mice (right top and bottom panels). MKs are indicated by yellow arrowheads (n = 3 mice per genotype). Bright field images were obtained using a Zeiss Axiovert 200 inverted high-end microscope with a 20× objective. Scale bar, 50 μm. (D-E) Determination of MK numbers per visual field (294 × 221 μm, 36 fields of view from 3 mice per genotype) in hematoxylin and eosin-stained spleen (D) and BM (E) sections of Vps33b^fl/fl vs Vps33b^fl/fl-ER^T2 mice. Mean ± SEM. All values are mean ± standard deviation (SD) unless otherwise indicated. ***P < .001.