Thalidomide induced vascular defect during the development of zebrafish embryos. Zebrafish embryos were treated at 75% epiboly stage (8 hpf) without (A,C,E,G) or with 800 μM thalidomide (B,D,F,I) and examined at the indicated hpf stages. (A-D) Lateral view of fixed embryo shows that thalidomide-treated embryos (B) are shorter in length than the control (A), as indicated by white arrows. Hematoxylin and eosin staining for the transverse section of thalidomide-treated embryos shows that the lumens of the dorsal artery (marked “A” in panel C) and posterior cardinal vein (marked “V” in panel C), which are evident in the control embryo (C), are lost in the thalidomide-treated embryo (D). (E-J) In situ mRNA hybridization is performed for endothelial markers neuropilin-1 (E,F) and FLK-1 (G-J). Expressions of neuropilin-1 and FLK-1 are absent at the region corresponding to dorsal artery and vein (indicated by boxes) after treatment with thalidomide (F,I). The defect of FLK-1 expression at large vessels is more evident by a higher magnification (H,J). The results are representative of each experiment. noto indicates notochord; A, dorsal artery; V, posterior cardinal vein; hpf, hours after fertilization. Original magnification of panels A, B, E, F, G, and I is ×40; of C and D, ×150; and of H and J, ×63. The images were visualized using an Olympus BH2 Biological microscope equipped with an SPlan APo20 20×/0.70 objective lens and a C-35AD-2 camera (Olympus, Tokyo, Japan) or a Nikon Stereoscope SMZ1000 microscope equipped with a Plan Apo 1×/0.10 objective lens with zoom system covering the total magnification to 40× and 60×, and an FDX-35 camera (Nikon, Tokyo, Japan). Images were processed with Adobe Photoshop 7.0 software (Adobe Systems, San Jose, CA).