Ripply-mediated Xbra inhibition is required for proper head development

Abstract

Spemann ’ s Organizer induces dorsal and anterior fate to nearby tissues and make head and body axis in Xenopus embryos. Various molecules have been discovered to mediate this organizing activity. We found Ripply as a noble organizer gene through microarray analysis. Ripply has been reported as a somitogenesis regulating factor. Ripply binds to Tbx6 and transforms Tbx6 to a transcriptional repressor in developing somites by recruiting Groucho/TLE corepressors. However, Ripply was also expressed in dorsal mesendoderm of early gastrula and in head organizer of late gastrula. Ectopic expression of Ripply induced blastopore closure defects and neural tube closure defects, while knockdown of Ripply induced truncated head. In molecular level, Ripply interacted with Xbra, and inhibited the target genes of Xbra. Ripply knockdown resulted in the reduction of head-related genes such as Goosecoid and Otx2. These result suggest that Ripply maintains the fate of the head mesoderm by inhibiting Xbra, and this function is necessary for proper head development.