Fig. 2. Treatment with recombinant GREM1 enables upregulation and propagation of Wnt11 and Gdnf expression in Grem1-deficient kidney rudiments in culture. Mouse kidney primordia were isolated at E10.75-11.0 (38-42 somites) and cultured for 48 hours either without (A,B,D,E) or in the presence of recombinant GREM1 (5 µg/ml, C,F). All upper panels show the epithelial branching pattern as revealed by the Hoxb7-GFP transgene. Lower panels show transcript distributions as revealed by whole-mount in situ hybridisation. Ureteric buds are indicted by white asterisks, ectopic epithelial buds by red asterisks. (A-C) Gdnf expression: (A) wild-type control; (B) Grem1-deficient kidney primordia, note the smaller size and remaining Gdnf expression; (C) Grem1-deficient kidney primordia cultured in the presence of recombinant GREM1. Note the ectopic epithelial buds and Gdnf expression in the surrounding mesenchyme. (D-F) Wnt11 expression (D) wild-type control; (E) Grem1-deficient kidney primordia, note the complete loss of Wnt11 expression; (F) Grem1-deficient kidney primordia cultured in the presence of recombinant GREM1. Wnt11 is expressed in the epithelial tips of both ureteric and ectopic buds.