Gross phenotype of Bmpr2-deficient mice. (A) Massive bleeding in the cecum. Tissues from a WT littermate are shown in comparison. (B) H&E-stained sections (right) of a segment of ileum (left) from a Bmpr2 KD mouse. Arrowheads indicate extravasated erythrocytes in the lamina propria. (C) Vascular lesions in the cutaneous extremities. The lesions appeared as redness under the nail bed and dilated capillaries in the histology sections (arrows). Wild-type tissue is shown in comparison. (D) Enlarged spleen as a result of regenerative response to anemia in Bmpr2 KD mice. The follicles were disorganized, and there were clear signs of extramedullary hematopoiesis. See “Materials and methods, Histopathology, immunohistochemistry, and immunoblotting” for detailed image acquisition information. (E) Survival curves of mice hemizygous (shRNA 1×) or homozygous for the shRNA transgene (shRNA 2×). The bar graph represents the relative Bmpr2 mRNA expression in the lung of mice with either one of 2 copies of the shRNA transgene, as determined by RT-PCR. Values are means plus or minus SD. *P < .01.