Expression of the mouse Folr1 gene in the visceral endoderm. Sagittal (A) and transverse (B) sections from mouse decidua at 7.5 days’ gestation were hybridized with an antisense riboprobe specific for the murine Folr1 gene. Strong expression was observed in the visceral endoderm, with weaker signal in the chorion, and no expression detectable in the embryo itself. Abbreviations: ave, anterior visceral endoderm; ch, chorion; d, deciduum; ec, ectoderm; h, headfold region; m, mesoderm; ve, visceral endoderm.