Fig. 4. osr1 is required for glomerular morphogenesis. (A,B) Expression of wt1a in control (A) and osr1 morphants (B) at 26 hpf. (C,D) Histological cross-sections of the 26 hpf glomerular progenitors in wild-type (C) and osr1 morphants (D) show equivalent expression of wt1a (arrows). (E,F) Cross-section of wild-type glomerulus at 48 hpf (E) shows wt1a expression in the midline vascularized glomerulus (arrow), whereas in osr1 morphants (F) wt1a-positive podocytes remain in an immature state (arrows) and fail to coalesce to the midline. (G,H) Expression of the podocyte marker nephrin is lost in osr1 morphants (arrowhead, H) when compared with the control embryos (arrowhead, G). Segment-specific loss of ae2 expression in the proximal pronephros is evident in the osr1 morphants (H) when compared with controls (G) at 48 hpf.