Ectopic Pax2 and Sox9 expression in lotus tetragonolobus lectin (LTL)-negative proximal tubule–derived cystic segments in P21 Six2creFRS2α knock-out (KO) kidneys. A and B: Co-immunofluorescence for Pax2 (red) and LTL (green) in P21 control and Six2creFrs2αKO kidneys. A: In controls, Pax2 expression is absent in LTL-positive proximal tubules (arrowhead) and present in LTL-negative tubules (likely collecting ducts) (arrow). B: In Six2creFrs2αKO kidneys, Pax2 again is absent in all LTL-positive segments, both in nondilated tubules and cysts, but is expressed ectopically in LTL-negative cystic segments (concave arrowheads) and expressed in nondilated LTL-negative tubules (likely collecting ducts) (arrowheads). Arrow indicates Pax2 expression in LTL-negative tubules (likely collecting ducts). C and D: Co-immunofluorescence for Sox9 (red) and LTL (green) in P21 control and Six2creFrs2αKO kidneys. C: In controls, Sox9 expression is absent in LTL-positive proximal tubules (arrowhead). D: In Six2creFrs2αKO kidneys, Sox9 is absent in nondilated tubules and cyst lining cells that robustly express LTL (arrowheads), but is expressed ectopically in cystic segments with reduced or absent LTL staining (concave arrowheads). Scale bars: 50 μm.