Number of glomeruli is increased in the kidney of transgenic mice expressing the truncated type II activin receptor

Histological analyses of the kidney were performed in transgenic mice expressing the truncated type II activin receptor. In these mice, signaling through the activin receptor was attenuated. Size and wet weight of the kidneys were identical to those of normal mice. Histologically, the number of glomeruli was approximately 180% of that in normal mice. The sizes and shapes of the glomeruli were variable, but many of them were smaller than those in normal mice. Morphometrically, the total glomerular area was 130% of that of the normal mice. Abnormality of the epithelia in Bowman's capsule was observed and the number of tubular epithelial cells was increased in the transgenic mice. The serum levels of blood urea nitrogen, creatinine, and creatinine clearance were identical to those in normal mice. These results suggest that the action of activin or related ligands is critical for determination of the nephron number.