Fig. 7. (A) Gdnf rescue of Flk1 blockade. (a) Flk1 block and (b) Flk1 block with addition of Gdnf are stained for cytokeratin (red) and proximal tubule-binding lectin (green). (a,b) From the same embryo. (c) Terminal branch number (P<0.001) and (d) tubule number (P<0.001) quantification from four pairs of cultures represented by (a) and (b). (B) Pax2 in situ hybridization of organ cultures from E11.5 embryos cultured for 48 hours in the presence of (a) Flk1 block and (b) Flk1 block with addition of Gdnf. (C) Late addition of Flk1 blockade. (a,b) Organ cultures from the same embryo, obtained from E11.5 embryos, cultured for 48 hours before addition of Flk1-blocking antibody (b) or control IgG (a), and cultured for an additional 48 hours. (c,d) Quantitation of four pairs of organ cultures represented by (a) and (b). Differences are not significant.