(A–E) IHC staining for GATA4 protein in transverse sections of control and Gata4 cKO embryos. Sections were chosen to represent similar anterior positions in genital ridges. Right panel shows higher magnification of boxed area in left panel. Arrows indicate examples of positive GATA4 staining. Red dashed lines mark boundary between coelomic epithelium and underlying mesenchyme. Control and conditional mutant embryos, except for Gata4 cKO (CAG-CreER), were from the same litter. a, dorsal aorta; g, gut endoderm; ge, genital ridge epithelium; gm, genital mesenchyme; m, mesentery; mt, mesonephric tubule. (F) Immunofluorescent staining for laminin protein in sections of control and Gata4 cKO embryos. Laminin marks basement membrane. Control genital ridge shows thickened epithelial layer (yellow bracket), whereas the coelomic epithelium in Rb cKO embryo remains a single-cell layer (yellow dashed line). Scale bars: 50 µm.