Primary cilium disappearance in podocytes during vertebrate phylogeny revealed by array tomography

Podocytes are a type of epithelial cells that form the kidney nephron and are essential for ultrafiltration in the glomerulus. The majority of nephron constituent cells have primary cilia, which play an important role in the maintenance of normal tubular architecture of nephron. However, whether podocytes have primary cilia was only partially understood. In general, immunohistochemistry with an anti-acetylated α-tubulin antibody is often used to visualize primary cilia. α-Tubulin is highly acetylated throughout podocytes, and this antibody is not suitable to determine the presence or absence of primary cilia in podocytes, which is one reason why the presence of primary cilia in podocytes has remained unclear. In the present study, we determined the presence or absence of primary cilia in mature podocytes of six vertebrate species using a recently reported array tomography workflow optimized for whole glomerulus analysis. The proportion of podocytes with primary cilia tended to decrease with evolution as follows: 89.6% in river lampreys (Agnatha), 42.1% in zebrafish (Osteichthyes), 43.3% in African clawed frogs (Amphibia), 17.3% in Reeves' turtles (Reptilia), 10.4% in common quails (Aves), and 0.0% in Wistar rats (Mammalia). Our previous study has reported that, in rats, primary cilia are present in podocytes during development and disappear in mature podocytes. In other words, primary cilia disappear from podocytes during both phylogeny and ontogeny in vertebrates. We discuss the triggers and significance of primary cilium disappearance from vertebrate podocytes.