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

<p>(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. (<b>A</b>) 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,B′,C,C′</b>) 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. (<b>D,D′</b>) 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. (<b>E</b>,<b>F</b>) 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. (<b>G</b>) 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. (<b>H</b>) Strong CXCR4-GFP signals are detected only in cap mesenchyme (cm). All scale bars equal 20 µm.