Endoglin is expressed in blood and endothelium in the developing embryo. (A) In situ hybridization (ISH) for Eng RNA in an E10.5 embryo. (i) Sagittal section of a paraffin embedded whole-mount embryo (×4); endoglin (black-purple stain) is expressed in the lining of the cardiac chambers (H), DA, FL (boxed), and vasculature of multiple tissues. (ii) Magnified view (×20) of the DA showing concentration of Eng RNA in the hemogenic endothelium (↑) and in blood clusters (boxed). (iii) Magnified view (×40) of the FL. (B) Endoglin expression at E11.5. (i) ISH for Eng RNA. Transverse cryosection (×20) of an embryo at the level of the AGM shows expression in FL and DA. The inset shows a magnified view (×40) of the DA with Eng RNA concentrated in blood clusters (↑). (ii) Flow cytometry plots showing Eng (CD105) expression in approximately 3% of FL cells. DA, dorsal aorta; FL, fetal liver; H, heart.