Fig. 2. Gcm1, Synb and Cebpa are expressed in SynT-II cells and Syna is expressed in SynT-I cells. (A) Electron micrograph of the trilaminar trophoblast structure that separates the maternal and fetal blood compartments. The black box indicates the area shown at high-magnification on the right. S-TGC, sinusoidal trophoblast giant cell; SynT-I, syncytiotrophoblast layer I; SynT-II, syncytiotrophoblast layer II; Endo, fetal endothelial cell; m, maternal blood space; f, fetal blood space; frbc, fetal red blood cell. (B) Double in situ hybridization for Syna (brown) and Synb (purple) in the labyrinth at E14.5 indicating that Syna expression is restricted to SynT-I cells and Synb expression is restricted to SynT-II cells. Note that Syna/Gcm1 and Syna/Cebpa double in situ hybridizations produced similar results (data not shown). Black arrowhead indicates unstained S-TGC which lines maternal blood spaces. Brown arrowhead indicates Syna-positive SynT-I cells located closer to maternal blood spaces. Blue arrowhead indicates Synb-positive SynT-II cells located closest to fetal blood spaces. (C) Double in situ hybridization for Ctsq (brown) and Synb (purple) in the labyrinth at E14.5. Black arrows indicate unstained SynT-I cell between Ctsq-positive S-TGC and Synb-positive SynT-II cell. (D) Double in situ hybridization for Syna (purple) and Synb (brown) in the labyrinth at E9.5. Syna and Synb expression do not co-localize. Note that Syna/Gcm1 and Syna/Cebpa double in situ hybridizations showed similar results (data not shown). (E) Double in situ hybridization for Syna (purple) and Synb (brown) in chorion at E8.5. Syna and Synb expression do not co-localize at E8.5 and demarcate distinct trophoblast populations within the chorion. Note that Syna/Gcm1 and Syna/Cebpa double in situ hybridizations showed similar results (data not shown). Scale bars: 100 µm (left); 50 µm (right).