Figure 2. Differential expression of CXCR7 and CXCR4 in nephrogenic mesenchyme, ureteric bud, and forming glomeruli.

(A–D) A digoxigenin (DIG) labeled WT1 antisense probe was used as a marker for mesenchymal and mesenchyme derived nephrogenic structures at E14.5 and co-hybridized with ³⁵S labeled probes for CXCR7 or CXCR4. (A) Strong CXCR7 signals (black grains) are present in a T-shaped WT1 negative early ureteric bud tip (eub) which is associated with a CXCR7/WT1 co-positive pretubular aggregate (pa; black grains/brown staining). Weaker CXCR7 expression is found in a late ureteric bud tip (lub) which is associated with CXCR7/WT1 co-positive renal vesicles (rv). Note weak CXCR7 mRNA expression in the cap mesenchyme (cm) and strong CXCR7 gene activity above the cm (brown staining) at the renal capsule (rc). (B,B′,C,C′) Bright- and darkfield views of a comma-shaped body (cb in B) and S-shaped body (sb in C) after hybridization with a DIG labeled WT1 probe and a ³⁵S labeled CXCR7 riboprobe (black grains in B,C; white grains in B′,C′). Both WT1 positive structures exhibit clear CXCR7 antisense mRNA signals. (D,D′) Bright- and darkfield micrographs showing WT1-positive renal tissue (D) and radiosignals of CXCR4 riboprobe (D′). Strong CXCR4 gene expression is detected in a WT1 negative early ureteric bud tip (eub in D, dotted line in D′). Weak CXCR4 labeling is seen in a late ureteric bud tip (lub) which is associated with a WT1 positive/CXCR4 negative renal vesicle (rv). Note that CXCR4 mRNA is also present in WT1 positive cap mesenchyme (cm). WT1 positive epithelial cells of S-Shaped bodies display no CXCR4 mRNA expression. The vascular cleft of S-shaped bodies (arrows in D′) as well as putative arterioles (arrowhead in D′) are CXCR4 positive. (E,F) GFP immunostaining in sections from BAC transgenic mice expressing EGFP under the control of the CXCR7 promotor (G) or CXCR4 promotor (H). Calbindin was co-stained as an ureteric bud marker. (G) CXCR7-GFP is highly expressed in the renal capsule (rc) as well as in comma- and S-shaped bodies (cb, sb) associated with a calbindin positive late ureteric bud (lub). CXCR7-GFP is weak expressed in cap mesenchyme (cm) and not present in the late ureteric bud. (H) Strong CXCR4-GFP signals are detected only in cap mesenchyme (cm). All scale bars equal 20 µm.