Fig. 6. Knockdown of Sema3a1 by antisense MO disrupts the migration of putative neuropilin 1-positive angioblasts and the formation of the dorsal aorta. (A) Heat induction of ^GFPSema3a1^myc was significantly reduced in a hsp70:^gfpsema3a1^myc embryo at 25 hpf by prior injection of antisense sema3a1 antisense MO (left), but not by injection of sema3a1 control MO (right). (B,C) There are fewer neuropilin 1-expressing cells than normal between the notochord and yolk tube in a 22 hpf antisense sema3a1 MO-injected wild-type embryo seen in a lateral view (B, compare with Fig. 2E) and a transverse section (C, compare with Fig. 2J). Some neuropilin 1-positive cells can be seen just ventral to the notochord but the strips of cells extending dorsally from the yolk tube are missing. (D) Normal pressures that would label the dorsal aorta and the cardinal vein in the trunk of wild-type embryos with Berlin Blue ink only label the cardinal vein in 30 hpf embryos injected with sema3a1 antisense MO. (E) Higher pressures that lead to rupture of the cardinal vein (asterisk) sometimes labeled the dorsal aorta, but the aorta was severely constricted (arrow) in 30 hpf embryos injected with sema3a1 antisense MO. Scale bar: 20 µm.