Transplanted OSE organoids also can give rise to HGSOC. a Representative serial images of OSE organoid at the indicated times after seeding; magnification: ×10, scale bar, 20 μm. b Left panel: H&E stain of OSE organoid; Middle panel: IF for E-cadherin and Ki67; Right panel: IF for PAX8 in FTE (FT) and OSE (O) organoids. Note that only FTE organoids are strongly PAX8+. Scale bar, 20 μm. c Representative flow cytometric plot, showing gates used to purify EGFPhi and EGFPneg populations from Lgr5-GFP OSE cells (Left panel). Bright field pictures show organoids that developed from FACS-purified cells (Middle panel). Right panel shows organoid-forming efficiency of the two populations. Data indicate means ± SEM, ***p < 0.001, unpaired t test. d Representative immunoblot for T121 in LPT organoids without 4-OHT treatment and 2 weeks after 4-OHT induction; ERK2 serves as a loading control. Wt: wild type organoid. e Micrographs of typical OSE organoids from mice of the indicated genotypes after 6 days culture. f Relative organoid-forming efficiency of OSE cells from mice of the indicated genotypes; Data represent means ± SEM; ns not significant, Tukey’s multiple comparison test. g Growth curves of OSE organoids from the indicated mice; Cells per well were counted at each passage from P1–P3 and P4–P6. Organoids from three independent mice for each group were used, each in duplicate. (Source data are provided as a Source Data file.) Data represent means ± SEM, **P < 0.01, ***P < 0.001, two-way ANOVA. h Gross pictures of OSE organoids transplanted into the MFP (left panel, 5 months post-injection of 105 OSE organoid cells) or the ovarian bursa (right panel, 4 months post-injection of 105 OSE organoid cells) of nu/nu mice. i % of tumors formed in mice within 6 months after injection of 105 cells from wild type, LP, LP, or LPT organoids (all 4-OHT-treated), n = 10 mice/group; ***P < 0.001, Fischer’s exact test. j and k Representative H&E staining and IHC for the indicated markers in LPT organoids (top) and the orthotopic tumors derived from these organoids, 4-months post injection of 105 cells (bottom).