Retinoic acid induced expression of Hnf1β and Fzd4 is required for pancreas development in <i>Xenopus laevis</i>

Retinoic acid (RA) is required for pancreas specification in <i>Xenopus</i> and other vertebrates. However, the gene network that is directly induced by RA signalling in this context remains to be defined. By RNA sequencing of <i>in vitro</i>-generated pancreatic explants, we identified the genes encoding the transcription factor Hnf1β and the Wnt-receptor Fzd4/Fzd4s as direct RA target genes. Functional analyses of <i>Hnf1b</i> and <i>Fzd4</i>/<i>Fzd4s</i> in programmed pancreatic explants and whole embryos revealed their requirement for pancreatic progenitor formation and differentiation. Thus, Hnf1β and Fzd4/Fzd4s appear to be involved in pre-patterning events of the embryonic endoderm that allow pancreas formation in <i>Xenopus</i>.