Figure 6.

Immunohistochemical detection of SIX1 and SALL2 proteins in human fetal kidney and in WTs. A: Serial sections of a 20-week gestation human fetal kidney were developed with anti-SIX1 and anti-PAX2 + 8 polyclonal antisera. SIX1 is expressed only in the earliest condensing mesenchyme (metanephric blastema), which is seen directly apposed to the uretic bud-derived epithelium. PAX2 + 8 detects expression of these two proteins in the condensing mesenchyme, and there is a strong signal in differentiating epithelial structures (S-shaped and comma-shaped bodies) deeper in the kidney, 8,50 as well as in ureteric bud. 36 Weak cytoplasmic staining in differentiated epithelial cells is nonspecific (seen in control with secondary antibody alone). B: SIX1 is expressed in the blastemal component of WTs (asterisks), but not in the epithelial areas (arrows). This pattern was seen in three of three cases of WT examined. In these same cases the epithelial component stained strongly with anti-PAX2 + 8 (not shown). C: Anti-SALL2 polyclonal antiserum gives a strong and uniform signal in the condensing mesenchyme, but cells with nuclear SALL2 are also seen at lower frequencies and with somewhat reduced staining in differentiating epithelial structures. Ureteric bud derivatives are negative for SALL2. Weak cytoplasmic staining in differentiated epithelial cells is nonspecific. CM, condensing mesenchyme; U, ureteric bud branches; Ep, differentiating epithelial structures; Gl, primitive glomeruli; Tu, differentiated renal tubules.