To identify the tubular segment involved in cyst formation, we stained for different tubular segment markers, i.e., aquaporin 2 (AQP2) for collecting ducts, CD13 and aquaporin 1 (AQP1) for proximal tubules and Tamm–Horsfall protein (THP) for the thick ascending limb (TAL). This evidence concerns the gene ANPEP and cyst.