Establishment and characterization of Meta1 gastroid lines. (A) H&E staining shows the stomach mucosa used for the generation of the Meta1 and Meta4 gastroids displaying pyloric metaplasia and dysplasia, respectively. Immunofluorescence staining for SPEM cell markers (AQP5 and GSII) and a dysplastic marker (TROP2). Scale bar: 50 μm. (B) Schematic illustration of the gastroid establishment process from Mist1-Kras transgenic mice. (C) Representative bright field images of Meta1 gastroids captured at day 0, 3, and 7 days after plating. Scale bars: 50 μm for first picture and 100 μm for second and third. (D) Immunofluorescence staining of Meta1 gastroids cross sections for SPEM markers (CD44v9, AQP5, and TFF2). Yellow arrows and enlarged sections indicate presence of mature SPEM cells triple positive for CD44v9, AQP5, and TFF2 in cells. Scale bar: 100 μm.