Immunofluorescence Staining of FFPE Cysts

The formalin-fixed paraffin-embedded (FFPE) samples of three subarachnoid and four vesicular cysts were cut into 4 µm sections placed on poly-l-lysine coated slides and treated as previously described^{22 (link),23 (link)}. The slides were submerged in 10 mM citrate buffer (10 mM citric acid, 0.05% Tween 20, pH 6.0) for 30 min at 95 °C, incubated for 30 min with a blocking solution (PBS pH 7.2, 0.05% Tween 20, 0.1% Triton X-100, 2% goat serum, 2% BSA) in a humid chamber at RT, then incubated overnight at 4 °C with primary antibody in PBS (Supplementary data 5), washed three times for 2 min with washing solution (PBS pH 7.2, 0.05% Tween 20) and then incubated for 30 min at RT with the fluorescein-labeling goat anti-rabbit antibody (Jackson ImmunoResearch Lab, West Grove, PA, USA) diluted 1/500 in PBS. The sections were then washed with PBS and mounted with VectaShield mounting medium with DAPI (Vector, Laboratories, Burlingame, CA, USA). Images were captured by confocal microscopy (Zeiss, LSM880, Oberkochen, Germany).