Fig. 1. Expression of NRP1 becomes restricted to the arterial compartment of the blastodisc. Whole-mount in situ hybridizations with the indicated antisense riboprobes. (A) 4ss, NRP1 is expressed throughout yolk sac blood islands and in the heart anlage (arrow). (B) 14ss, (C) 21ss. NRP1 expression is lost from EC in the anterior lateral mesoderm (asterisk in A-E). Arrowheads in B point to the dorsal aorta. (D) VEGFR2 labels both anterior and posterior lateral mesoderm at the 14ss. (E) 25ss. NRP1 expression is observed in the omphalomesenteric arteries (arrows) and their branches. (F) Schematic representation of the embryonic and extra-embryonic circulation at the 25ss (redrawn from Gilbert, 1994).