Fig. 3

nephrin and podocin are exclusively expressed in the pronephric glomerulus. Nephrin is expressed in the forming glomerulus starting at 24 hpf (A) and continues to be expressed at 48 hpf (B) and 72 hpf (C). Expression of podocin at 36 hpf (D) marks the podocyte precursor cells; at 48 hpf (E), podocin positive nephron primordia lie adjacent to each other. Cross-sections at 72 hpf show the glomerular expression of nephrin (C) in a localization typical for podocytes surrounding the glomerular capillary tuft (C, arrow). At 120 hpf (F), nephrin expression is strong in podocytes adjacent to the capillary tuft (*) originating from the dorsal aorta (da). Endothelial cells in the aorta and the glomerular capillaries are negative for nephrin expression. Diffuse staining for both probes in the head was not strong or reproducible and most likely represents optical summation of background staining. Spots of dark pigment in the trunk in panel A are not nephrin expressing cells but rather pigment cells that escaped PTU treatment (gl, glomerulus; liv, liver; nc, notochord; da, dorsal aorta).