Molecular organization of the GBM and the SD. (A) Highly stratified assembly of GBM components. Laminin LM-521 and agrin are bimodally distributed, whereas collagen IV complexes are concentrated at the core of the GBM. The minor α1α1α2 collagen (Col) is notably biased toward the glomerular endothelium. Both the predominant α3α4α5 and the less abundant α1α1α2 type IV collagens are normally too distant from β1–integrin receptor (IR) complexes on the podocyte side. This suggests that LM-521 and agrin but not type IV collagens are the normal physiological ligands of IR complexes expressed by podocytes. (B) Simplified representation of major adhesion receptors (nephrin, Neph1, and Fat1) found in the SD. Lipid-raft localization of the SD is dependent on the cholesterol-binding podocin. The SD is coupled to both F-actin regulatory (Nck–N-WASP–Arp2/3 and CD2AP–Arp2/3) and cell polarity (Par6–aPKCλ/ι–Cdc42) complexes.