etsrp RNA Overexpression Induces Ectopic Expression of Vascular Endothelial Markers Dorsal view, anterior to the left in all panels except for (E,F) which are lateral views. (A, C, E, and G) Control uninjected embryo; (B, D, F, and H) 100 pg of etsrp RNA-injected embryo. (A,B) scl expression at the eight-somite stage; (C,D) flk1 expression at the nine-somite stage. Note the strong ectopic induction of scl and fli1 upon overexpression of etsrp RNA. (E,F) Live flk1-GFP embryo at the 14-somite stage; fluorescent and transmitted light images were overlayed. Note the very strong ectopic induction of GFP expression in different tissues including neuroectoderm (arrow, F) upon etsrp RNA overexpression. Fluorescence in the control uninjected flk1-GFP embryo in (E) is not detectable under the same exposure. (G,H) gata1 expression at the 16-somite stage. Note that gata1 expression is not affected upon etsrp overexpression. (I–L) etsrp RNA induces flk1 expression in clo mutant embryos as analyzed using flk1 probe at the ten- to 12-somite stages. (I) wt (or clo+/-) embryo, (J) wt (or clo+/-) embryo injected with 100 pg of etsrp RNA, (K) clo-/- embryo, (L) clo-/- embryo injected with 100 pg of etsrp RNA. Note that in a clo+/- (or wt) embryo etsrp RNA induces ectopic flk1 (arrow, J) in addition to the endogenous flk1 expression (arrowheads, J) while clo-/- etsrp RNA-injected embryo shows only ectopic flk1 (arrows, L).