Editing Gastrulation (section)

== Cell signaling driving gastrulation ==
During gastrulation, the cells are differentiated into the ectoderm or [[mesendoderm]], which then separates into the mesoderm and endoderm.<ref name="Zorn A-2009"/> The endoderm and mesoderm form due to the [[nodal signaling]]. Nodal signaling uses ligands that are part of [[Transforming growth factor beta|TGFβ]] family. These ligands will signal transmembrane serine/threonine kinase receptors, and this will then phosphorylate [[Mothers against decapentaplegic homolog 2|Smad2]] and [[Mothers against decapentaplegic homolog 3|Smad3]]. This protein will then attach itself to [[Mothers against decapentaplegic homolog 4|Smad4]] and relocate to the nucleus where the mesendoderm genes will begin to be transcribed. The [[Wnt signaling pathway|Wnt pathway]] along with [[Beta-catenin|β-catenin]] plays a key role in nodal signaling and endoderm formation.<ref>{{Cite journal |pmid = 17307341|year = 2007|last1 = Grapin-Botton|first1 = A.|title = Evolution of the mechanisms and molecular control of endoderm formation|journal = Mechanisms of Development|volume = 124|issue = 4|pages = 253–78|last2 = Constam|first2 = D.|doi = 10.1016/j.mod.2007.01.001|s2cid = 16552755|doi-access = }}</ref> [[Fibroblast growth factor]]s (FGF), canonical Wnt pathway, [[bone morphogenetic protein]] (BMP), and [[retinoic acid]] (RA) are all important in the formation and development of the endoderm.<ref name="Zorn A-2009" /> FGF are important in producing the [[homeobox]] gene which regulates early anatomical development. BMP signaling plays a role in the liver and promotes hepatic fate. RA signaling also induce homeobox genes such as Hoxb1 and Hoxa5. In mice, if there is a lack in RA signaling the mouse will not develop lungs.<ref name="Zorn A-2009" /> RA signaling also has multiple uses in organ formation of the pharyngeal arches, the foregut, and hindgut.<ref name="Zorn A-2009" />