EHBD-derived organoids originate from and continue to express PROM1+ PBG-residing biliary progenitor cell phenotype. (A) EHBD-derived biliary organoids universally express PROM1 (red) along the luminal surface of the organoids as well as universally express SOX9 (green). PROM1 expression is absent in Prom1
KO organoids, but SOX9 expression is maintained. Triangles point to organoid luminal surface; stars indicate basolateral surface. Scale bar, 20 μm. (B) Prom1
Cre/+-GFP
+/− EHBD were partially digested after tamoxifen injection 1 week prior, placed in Matrigel and organoid culture media, and imaged at 5 days after culture. GFP+ organoids can be seen budding from GFP+ PBGs. GFP+ organoids increase over time and is associated with a decreased in PBG-like structure. Triangles indicate PBGs. Scale bar, 100 μm. (C) Organoids derived from Prom1
Cre/+-mTmG
+/− EHBDs with tamoxifen injection 1 week before EHBD dissociation display both GFP+ (green) and Tomato+ (red) expressing cells at 2 days of culture. Only GFP is expressed by day 6. Scale bar, 1.7 mm. (D) Organoids derived from Prom1
Cre/+-GFP
+/− and Prom1
Cre/Cre-GFP
+/− both express GFP. Scale bar, 200 μm. (E) Organoids derived from a biliary remnant of a patient with Biliary Atresia at time of Kasai were found to be PROM1+/SOX9+. Scale bar, 10 μm. Abbreviations: EHBD, extrahepatic bile duct; GFP, green fluorescent protein; PBG, peribiliary gland; PROM1, Prominin-1; SOX9, sex-determining region Y-box 9.