Electron microscopy study of Nphs2−/− mice. (a to e) Mixed B6/129 genetic background. (a) Normal differentiation of foot processes (arrow) in a mature glomerulus of a 1-day-old wild-type mouse. (b) As a comparison, diffuse effacement of foot processes (arrow) in a 1-day-old Nphs2−/− mouse with podocyte microvilli formation is shown. (c) At high magnification, the SD (arrows) between regularly spaced foot processes is clearly visible in a 1-day-old wild-type mouse. (d) One-day-old Nphs2−/− mouse. Focally, foot processes are present in Nphs2−/− mice, but they are irregular in size and shape; the SD is replaced by irregular adhesions between adjacent cells (arrows). (e) Focal mesangiolysis (arrows) in a 7-day-old mouse. (f) 129 genetic background. Diffuse effacement of foot processes, collapse of the vascular tuft (arrow), and presence of large podocyte vacuoles (V) in a 24-day-old Nphs2−/− mouse. Magnifications: panels a and f, ×3,250; panels b and e, ×7,350; panels c and d, ×18,000.