Fig. 2. Sdf1/Cxcr4a signaling controls the migration of endodermal cells during gastrulation. (Aa-Ad) sox17 expression was examined by whole-mount in situ hybridization in misMO1-, cxcr4aMO1-, cxcr4aMO2- or sdf1MOs-injected zebrafish embryos at the 90% epiboly (9 hpf) stage. Lateral views, dorsal to the right. The migration of sox17-expressing endodermal cells in the animal-lateral region to the dorsal midline is delayed in the cxcr4aMO1-, cxcr4aMO2- and sdf1MOs-injected embryos (arrowheads). (Ba-Bd) Dorsal views of the mid-trunk region of Tg(sox17:EGFP) transgenic embryos at the three-somite (3s) stage. Anterior is to the top. The migration of EGFP-positive endodermal cells to the dorsal midline is delayed by the knockdown of either cxcr4a or sdf1. (Ca-Cd) Dorsal views of the pharyngeal and foregut regions of Tg(sox17:EGFP) transgenic embryos at 24 hpf. Anterior is to the top. Both the cxcr4a and sdf1 knockdown embryos show a splitting of the anterior gut (arrows). (Da-Gd) The expression of foxa3 (gut and its associated organs), cp (liver), pdx1 (pancreas) and ins (β-cells in pancreas) was examined in misMO1-, cxcr4aMO1-, cxcr4aMO2- or sdf1MOs-injected embryos at 48 hpf. The expression of foxa3 in the anterior part of foregut is lost in both the cxcr4a and sdf1 knockdown embryos (arrows, Db-Dd). Moreover, the liver is not formed (arrowheads, Ea-Ed), the pancreas is small and is not assembled properly (arrowheads, Fa-Fd), and insulin-producing β-cells in the pancreas do not cluster (arrowheads, Ga-Gd) in both the cxcr4a and sdf1 knockdown embryos. l, liver; p, pancreas; g, gut. Note also that no phenotypic differences in endoderm migration and organ formation among the cxcr4aMO1-, cxcr4aMO2- and sdf1MOs-injected embryos can be observed.