Deficiency of Nbeal2 in mice leads to GPS. (A) Transcript levels of Nbeal2 by qPCR in RNA isolated from in vitro cultured MKs. Results are normalized to levels of GP6 (n = 3). (B) Protein levels of Nbeal2 in platelets and MKs from Nbeal2^−/− and control mice. β-actin included as an internal loading control (n = 3). (C) Platelet count in Nbeal2^−/− and control animals (n = 13). (D) Mean platelet volume in Nbeal2^−/− and control mice (n = 13). (E) Size distribution of the gated platelet population visualized in a representative flow cytometry histogram (forward scatter). (F) Representative May-Grünwald Giemsa stain of blood smears. Arrows indicate the presence of platelets. Platelets are larger and appear gray in Nbeal2^−/− samples. Bars represent 20 μm. (G) Different degrees of splenomegaly were observed in Nbeal2^−/− mice beyond the age of 9 months. Age-matched control mice were used for comparison (n = 4). (H) A representative reticulin staining of bone sections from mice at 9 months of age showing myelofibrosis in Nbeal2^−/− marrow. Bars represent 200 μm. *P < .05.