Macroscopic and microscopic features of the spleen ofmFtz-F1 gene–disrupted mice. (A) Comparison of macroscopic features of wild-type spleens (Wild) and mFtz-F1gene–disrupted (KO) newborn mice. Arrowheads show red spots characteristic of the KO spleen. Photomicrographs of splenic tissues of the wild-type (B) and KO (C and D) mice stained with hematoxylin and eosin. Note the erythrocyte-rich region (encircled by arrowheads in C), probably corresponding to the red regions in (A). (D) Photomicrograph showing megakaryocytes in the spleen of KO mouse (arrowheads). Scale bars: 100 μm in B and C; 25 μm in D.