Extracellular matrix deposition around the dorsal aortae is increased in mDll4 overexpressing embryos: Immunofluorescence of cryosections from E8.5 DT and control embryos. (A,C,D) Fibronectin deposition around the dorsal aorta of a WT embryo. (B,E,F) DT embryo section showing increased amount of fibronectin surrounding the dorsal aorta, relative to control embryo. (G,I,J) Laminin deposition around the dorsal aorta of a WT embryo. (H,K,L) DT embryo section showing increased deposition of laminin surrounding the dorsal aorta, forming a more defined layer relative to the patchier deposition seen in the control embryo. Matrix protein coding genes expression is increased in mDll4 overexpressing embryos while matrix degrading enzymes coding genes are down-regulated. (M) RT-PCR results for Fibronectin, Laminin, Collagen-1, -4, MMP1, 2, 9 and TIMP1, 2, and 3 compared with WT and DT ECs. (N) Transcriptional analysis of mDll4 overexpressing embryonic ECs. Notch pathway genes (Hey1, Hey2, Hes5), arterial markers (Connexin37, EphrinB2), and cell-to-cell adhesion protein coding genes (VE-cadherin) are up-regulated as a consequence of Dll4 overexpression. Venous marker (EphB4) and VEGF receptors Flk1 and Neuropillin2 are down-regulated while Flt is up-regulated. VEGF-A expression, measured from whole embryo lysates, is not significantly altered in DT embryos. Robo4 is down-regulated, Unc5b is up-regulated and PlexinD1 is not significantly altered. Relative quantitative gene expression in DT embryos compared with WT (n = 3 per group). Values were normalized in relation to β-actin expression. *P < .01.