The double knockdown of sox7 and sox18 does not cause gross morphologic abnormalities but selectively affects trunk/tail blood circulation. Control embryos (A,C,E) were injected with a dose of std-MO (0.5 pmol) corresponding to the total dose of MOs injected in the double morphants. Low doses of sox7-MO1 and sox18-MO1 (0.25 pmol) were not causing gross morphologic defects when injected separately (Figure S3) or coinjected (DMO) (B,D,F). More than 90% of the double morphants showed no sign of trunk/tail blood circulation, while minor circulatory defects were detectable in single morphants (Table S1). (A,B) Control embryo and double morphant at 1 dpf. Images were taken at 32× magnification, anterior to the left. (C,D) control embryo and double morphant at 2 dpf. Images were taken at 25× magnification, anterior to the left. (E,F) control larva and double morphant at 3 dpf. Images were taken at 20× magnification, anterior to the left. By this stage, heart edema is clearly detectable in the double morphants (black arrow). (G-J) Images at 50× magnification of a control larva injected with std-MO (G), and 3 double morphants showing blood accumulation (black arrowheads) in the anterior trunk (H), in the heart to yolk region (I) where residual circulation is detectable, and in the eye region (J). Anterior to the left. (K,L) 132× magnification images of cross-sections at the level of the eye showing a control std-MO–injected embryo and a double morphant at 2 dpf. The black arrowhead points to blood accumulation in the inner optic circle in the double morphant. Anterior to the top.