Arterial markers are expressed in all endothelial cells while venous markers are absent in E9.0 DT embryos in situ hybridization. (A,D) hey1 mRNA, (B,E) notch1 mRNA. The Notch markers tested show concomitant expression in the aortae (DA) and ACV of DT embryos. Control embryos (D,E) only show expression of these genes in the endothelium of the aortae. (C,F) flk1 mRNA shows lowered expression in the DT embryos. (G,J) ephrin-b2 mRNA, (H,K) connexin37 mRNA. The arterial endothelial specific markers tested show concomitant expression in the aortae and ACV of DT embryos. Control embryos (J,K) only show expression of these genes in the endothelium of the aortae. (I,L) eph-B4 mRNA is not detectable in the ACV of DT embryos despite being detected in the ACV of control embryos (L).