The protocol of ISH was previously described (16 (link)). Specific regions of lefty1 and foxj1a were cloned into pGEM T easy vector (Promega). ISH probe vectors for cmlc1, dand5, spaw, and pan-akap12 were previously described (12 (link), 16 (link)) and primer sequences of lefty1 and foxj1a for ISH probe vectors are summarized in Supplementary Table S1. The protocol of whole-mount immunostaining for Tg(sox17:egfp) embryos was described previously (16 (link)). Mouse anti-Cdh1 (1:200, BD Biosciences) and goat anti-mouse AF546 (1:1000, Invitrogen) were used for immunofluorescence. Stained embryos were mounted in glycerol and images were obtained by an AxioCam ICC-1 camera (Zeiss) on a Stemi 2000C (Zeiss) for immunohistochemistry and an LSM700 confocal microscope (Zeiss) for immunofluorescence, respectively, and processed using ZEN 2012 software (Zeiss).