Expression of Ad4BP/SF-1 in fetal and newborn spleens and structural changes observed in the early stages of splenic development. Immunohistochemical analysis was performed using splenic tissues from wild-type (A) and KO (B) newborn mice and spleen of an E 14.5 mouse fetus. Arrowheads in (C) indicate tubular structure composed of Ad4BP/SF-1 immunoreactive cells. Inset: higher magnification of the tubular structure. Spleens of E16.5 fetuses of wild-type (D) and KO (E) mice were histologically examined with hematoxylin and eosin. Arrowheads in D indicate longitudinal sections of the tubular structures. Scale bars: 100 μm.