Morphological process of podocyte development revealed by block-face scanning electron microscopy.

Koichiro Ichimura,Shigeo Arai,Tatsuo Sakai,Tomoyo Nakao,Sakiko Enomoto,Takahiro Nonami,Masato Koike,Takayuki Miyaki,Kazuyoshi Murata,Naoyuki Miyazaki,Yuto Kawasaki,Soichiro Kakuta

doi:10.1242/jcs.187815

Abstract

Podocytes present a unique 3D architecture specialized for glomerular filtration. However, several 3D morphological aspects on podocyte development remain partially understood because they are difficult to reveal using conventional scanning electron microscopy (SEM). Here, we adopted serial block-face SEM imaging, a powerful tool for analyzing the 3D cellular ultrastructure, to precisely reveal the morphological process of podocyte development, such as the formation of foot processes. Development of foot processes gives rise to three morphological states: the primitive, immature and mature foot processes. Immature podocytes were columnar in shape and connected to each other by the junctional complex, which migrated toward the basal side of the cell. When the junctional complex was close to the basement membrane, immature podocytes started to interdigitate with primitive foot processes under the level of junctional complex. As primitive foot processes lengthened, the junctional complex moved between primitive foot processes to form immature foot processes. Finally, the junctional complex was gradually replaced by the slit diaphragm, resulting in the maturation of immature foot processes into mature foot processes. In conclusion, the developmental process of podocytes is now clearly visualized by block-face SEM imaging.

Highlights

Podocytes are highly complex epithelial cells that are specialized for glomerular ultrafiltration
Immature podocytes were columnar in shape and connected to each other by the junctional complex (JC), which migrated toward the basal side of the cell
When the JC was close to the basement membrane, immature podocytes started to interdigitate with primitive foot processes (FPs) under the level of JC

Summary

Introduction

Podocytes are highly complex epithelial cells that are specialized for glomerular ultrafiltration. Podocytes are said to be composed of three kinds of subcellular compartments, the cell body, primary process, and foot process (Fig. S1A1) (Kriz and Kaissling, 2000; Ichimura and Sakai, 2016). The cell body of the podocyte projects five to ten primary processes, and each primary process protrudes numerous foot processes. Podocytes interdigitate with each other and adhere to the glomerular basement membrane (GBM) via the foot processes to form a glomerular epithelium (Fig. S1D1-2). The intercellular junction of podocytes, which is called the “slit diaphragm” spans between the foot processes. The slit diaphragm and the GBM mainly prevent the leakage of plasma protein into the primary urine

Methods

Results

Discussion

Conclusion