A study by transmission electron microscopy of the developing glomerular filtration membrane in mouse kidney

Objective To study the ultrastructural changes of the developing glomerular filtration membrane in mice. Methods The glomerular filtration membrane of embryonic and postnatal mice was observed by transmission electron microscope. Results The analysis of filtration membrane components showed that during the development of the renal corpuscle, the height of maturing podocytes became remarkably reduced. The number of their foot processes steadily increased, and they became slimmer and filtration slit diaphragms began to appear between them. Subepithelial basement membrane appeared firstly, and then subendothelial basement membrane came in its wake, and the fusion of both led to the formation of a thick basement membrane. As the tuft of the capillary glomerulus grew, newly formed fragments of the basement membrane in the form of loops and outpockets started to be evident beneath epithelial podocytes. Endothelial cells became greatly flattened, and numerous fenestrae through the cells appeared. Conclusion During the development of the renal corpuscle, podocytes and endothelial cells differentiate to maturity gradually, podocytes are the earliest source of the basement membrane, then endothelial cells participate in its formation, from then on, the basement membrane is synthesized and renewed mostly by epithelial podocytes.