Fig. 3. Dorsal migration by putative angioblasts is interrupted by overexpression of sema3a1. In all panels, Nomarski and fluorescence images are overlaid. (A) DiI-labeled cells ventrolateral to the somites immediately following diI injection in an 18 hpf wild-type embryo. (B) Some of the diI-labeled cells have migrated dorsally by 22 hpf in the same embryo shown in A. Broken line designates the ventral boundary of the notochord. (C) Transverse section at 24 hpf of another embryo showing that some of the diI-labeled cells (arrowhead) labeled at 18 hpf had migrated to a position just ventral to the notochord. (D) DiI-labeled cells ventrolateral to the somites immediately following diI injection in an 18 hpf hsp70:^gfpsema3a1^myc transgenic embryo following heat induction at 15 hpf. (E) The diI-labeled cells failed to migrate dorsally and remained in ventrolateral positions at 22 hpf in the same embryo shown in D. Broken line designates the ventral boundary of the notochord. (F) Transverse section of a hsp70:^gfpsema3a1^myc transgenic embryo at 24 hpf showing that diI-labeled cells have not migrated dorsally and remain very ventral. Scale bars: 20 µm.