Expression analysis of endothelial marker fli1a and erythroid marker gata1 in double transgenic embryos Tg(fli1a:EGFP) Tg(gata1:DsRed) shows that vascular development is impaired in arhgef3-depleted embryos. At 30 and 48 hpf arhgef3 MO-injected embryos (B,D) showed a poor segregation of artery and vein compared with control embryos (A,C). Furthermore, arhgef3-depleted embryos exhibited an accumulation of gata1⁺ cells in the subaortic region (B,D). By 48 hpf, all gata1⁺ cells from the subaortic space of control embryos have entered the circulation (C), whereas in arhgef3 MO-injected ones a reduced number of gata1⁺ cells were observed in the circulation (D). (E-F) Transverse agarose sections (200-μm thick) of Tg(fli1a:EGFP) control embryos at 48 hpf show 2 distinct lumenized vessels, artery (E arrow) and vein (E arrowhead), whereas lumen formation of arhgef3 MO-injected ones is perturbed and axial vessels form a single tube (F arrow).