sox18 and sox7 are coexpressed in endothelial cells and their precursors. The expression of the 2 genes was analyzed by ISH at various developmental stages, alongside with known markers. The expression of the 2 genes in endothelial cells and their precursors appears to be largely overlapping, although sox7 starts being detectable, and fades away, slightly earlier than sox18. (A,C) 4 somites, 40× magnification; (B,D-F) 8 somites; white and black arrows point to the ALM and PLM, respectively. (G,H,J,K) 22 somites; the developing DA, PCV, and ICM are marked with white arrowheads, black arrowheads, and white asterisks, respectively. (I,L) 24 hpf; higher magnifications inserts on the right show expression in the DA, PCV, and ISVs. A black asterisk in panel I marks sox7 expression in the otic vesicles. (M,N) 36 hpf. In all images, embryos are shown anterior to the left. In flat-mount images (E,F), double ISHs are presented to show colocalization of sox7 and sox18 with the innermost fli1-positive cells in the PLM. (A-D,G,J) Dorsal views. (H-N) Lateral views.