Magp1 and integrin functionally interact in vivo during vascular development. A mixture of the disintegrin Echistatin and blue dextran was injected into the common cardinal veins of wild-type and magp1 MO–injected Tg(fli1/EGFP) embryos at 24 to 25 hours after fertilization by microangiography. Embryos successfully injected, as indicated by the blue fluorescence in the circulation (A), were selected for phenotypic analysis at 30 hours after fertilization. The head (B) and the tail (E) of a Tg(fli1/EGFP) embryo at 30 hours after fertilization. The head (C) and the tail (F) of a Tg(fli1/EGFP) embryo injected with 1 ng magp1 MO and Echistatin showing dilation of vessels in the midbrain–hindbrain region, around the eye (C, arrowheads) and the caudal vein (F, arrowheads). The head (D) and the tail (G) of a Tg(fli1/EGFP) embryo injected with 1 ng magp1 MO and heat-attenuated Echistatin, exhibiting no significant change in the vasculature compared with wild-type embryos. (H) Summary of 2 independent injection experiments; 1 ng magp1 morpholino and 9 nL 20 μM Echistatin solution were injected (see “Injection of the integrin antagonist Echistatin”). HA indicates heat-attenuated; N, number of embryos scored. Error bars indicate SEM. (A-G) Original magnifications, 10 ×.