Fig. 4. Dynamic changes in Grem1 and Bmp4 expression during initiation of metanephric kidney development in mouse. (A-D) Bmp4 distribution during initiation of metanephric kidney development. (A,B) GFP reveals the morphology of the nascent ureteric bud at E11.0 (40-42 somites; A) and after the first epithelial branching (E11.5, 48-50 somites; B). Asterisks in B indicate the tips of the ureter branches. (C,D) The Bmp4 transcript distribution was determined using a lacZ reporter gene inserted into the endogenous Bmp4 transcription unit (Bmp4:lacZ) in heterozygous embryos (Kulessa and Hogan, 2002), as detection by whole mount in situ hybridisation is not reliable. (C) At E11.0, Bmp4:lacZ is expressed by the mesenchyme surrounding the Wolffian duct (arrow) and ureteric bud (see also G). The dotted circle indicates the position of the ureteric bud (compare with A). (D) By E11.5, the Bmp4:lacZ expression is retained in the mesenchyme surrounding the Wolffian duct (arrow), while the metanephric mesenchyme is largely devoid of Bmp4. The dotted line indicates the position of the first branch (compare with B). (E,F) Grem1 expression in the mesenchyme. (E) At E11.0, Grem1 expression is highest in the mesenchyme around the ureteric bud (indicated by a dotted circle). (F) Subsequently (E11.5), Grem1 is expressed in the mesenchyme around the tips of first ureteric epithelial branch (indicated by dotted oval). (G,H) Detection of Bmp4 and Grem1 transcripts on transverse sections by in situ hybridisation. Sections are oriented with dorsal to the top. Note that the epithelium (indicated by a dotted line) expresses neither Bmp4 (G) nor Grem1 (H). (G) There is abundant Bmp4 expression in the mesenchyme around the caudal Wolffian duct and ureteric epithelium in agreement with the Bmp4:lacZ distribution shown in C. (H) At E10.75 (38 somites), Grem1 is also expressed in the mesenchyme around the caudal Wolffian duct and ureteric epithelium in agreement with the whole mount in situ hybridisation shown in E. Note that Bmp4 and Grem1 are also expressed by the mesenchyme around the hindgut. Hg, hindgut; mm,: metanephric mesenchyme; wd, Wolffian duct.