Editing Gastrulation (section)

===Cell internalization===
In order for the cells to move from the [[epithelium]] of the [[epiblast]] through the [[primitive streak]] to form a new layer, the cells must undergo an [[Epithelial-mesenchymal transition|epithelial to mesenchymal transition]] (EMT) to lose their epithelial characteristics, such as [[Cell adhesion|cell–cell adhesion]]. [[fibroblast growth factor|FGF]] signaling is necessary for proper EMT. [[FGFR1]] is needed for the up regulation of [[SNAI1]], which down regulates [[CDH1 (gene)|E-cadherin]], causing a loss of cell adhesion. Following the EMT, the cells [[ingression (biology)|ingress]] through the [[primitive streak]] and spread out to form a new layer of cells or join existing layers.  [[FGF8]] is implicated in the process of this dispersal from the [[primitive streak]].<ref name=Loebel />