Organoids were removed from culture media, re-crosslinked in 50 mM calcium chloride for 2 min, and fixed in 2% PFA with 50 mM sodium cacodylate and 10 mM calcium chloride for 16–24 h. All reagents were obtained from Vector Laboratories, Inc. (Burlingame, CA) unless otherwise indicated. Xylene and ethanol were obtained from Surgipath Medical Ind. Inc. (Richmond, IL). Antigen retrieval was performed using 10 mM sodium citrate, pH 6.0. Slides were washed in Tris-buffered saline (TBS) with Tween 20 [20 mM Tris, 500 mM NaCl, 0.1% Tween 20, pH 7.4]. When staining for BrdU, tissues were treated with 4M hydrochloric acid for 10 min, followed by 0.1 M sodium tetraborate for 10 min. Tissues were blocked for 15 min in 3% hydrogen peroxide (Fisher Scientific, Pittsburgh, PA) followed by avidin and biotin blocking according to manufacturer’s instructions. Slides were incubated in TBS-3%BSA-10% serum of the secondary antibody host for 1 h at room temperature. After blocking, slides were incubated overnight at 4°C in primary antibody in 3% BSA-TBS-10% serum. Control slides received serum block instead of the primary antibody. The primary antibodies against BrdU (rat, 1:200 dilution; Abcam, Cambridge, MA), CK8 (CK8 TROMA-1 antibody, rat, 1:200; Developmental Studies Hybridoma Bank, Iowa City, IA), E-cadherin (rabbit, 1:50; Cell Signaling Technology, Denver, MA), F4/80 (rat, 1:100; Abcam), acetylated tubulin (mouse, 1:500; Sigma Aldrich), oviductal glycoprotein 1 (OVGP1, rabbit, 1:250; Abcam), Pax8 (rabbit, 1:250 Proteintech Group, Chicago, IL), phospho-γH2A.X (rabbit, 1:100; Cell Signaling Technology), or SV40 T Ag (rabbit 1:50; Santa Cruz Biotechnology, Santa Cruz, CA) were incubated on tissue sections overnight at 4°C. Slides were rinsed three times for 5 min in TBS-Tween and then incubated at room temperature for 30 min in biotinylated secondary antibody in 3% BSA-TBS. After washing slides in TBS-Tween, avidin/biotin complex (ABC) reagent was added and incubated for 30 min at room temperature. Slides were washed in TBS and antigen-antibody-horseradish peroxidase complex was visualized using diaminobenzidine (DAB) reagent for 5 min. Slides were counterstained with hematoxylin.