Editing Gastrulation (section)

=== Cell signaling ===
In the frog, ''Xenopus,'' one of the signals is [[retinoic acid]] (RA).<ref name="Zorn A-2009">{{Cite journal|last=Zorn A|first=Wells J|date=2009|title=Vertebrate Endoderm Development and Organ Formation|journal=Annu Rev Cell Dev Biol|volume=25|pages=221–251|doi=10.1146/annurev.cellbio.042308.113344|pmid=19575677|pmc=2861293}}</ref> RA signaling in this organism can affect the formation of the endoderm and depending on the timing of the signaling, it can determine the fate whether its pancreatic, intestinal, or respiratory. Other signals such as Wnt and BMP also play a role in respiratory fate of the ''Xenopus'' by activating cell lineage tracers.<ref name="Zorn A-2009"/>