Figure 4. Transmission electron microscopy of mouse kidneys.

(A) Representative cross-sections of glomerular capillaries in the juxtamedullar zone of a wild-type mouse (age P2). Enlarged insets (right panels) show detailed endothelial cells (ec), GBM (arrowheads), and foot processes (fp) of the glomerular epithelial cells (podocytes) with well formed, open filtration slits (asterisks). (B) Representative juxtamedullary glomerular capillaries of a Gne^M712T/M712T mouse (age P2, littermate of the wild-type mouse shown in A), indicating segmental splitting of the lamina densa of the GBM (arrowheads) as well as dramatically flattened and fused podocyte foot processes lining the GBM. The filtration slits are sparse and irregular in shape and position. Insets (right panels) show fused foot process membranes and formation of abnormal tight junction-like structures at the filtration slits (diamonds). (C and D) Representative glomerular capillaries of a Gne^M712T/M712T mouse following ManNAc treatment (age P19). The integrity of the GBM as well as the formation of podocyte foot processes and the number of filtration slits were all improved when compared with the untreated Gne^M712T/M712T mouse in B. Some filtration slits were open, while others still formed tight junctions. The GBM showed occasional small stretches of areas where splitting was apparent (arrowheads). L, capillary lumen; N, nucleus; us, urinary space. Scale bars: 1 μm.