 Epithelial–mesenchymal transition occurs in embryonic cells that require migration through or over tissue, and can be followed with a mesenchymal–epithelial transition to produce secondary epithelial tissues.Embryological mesenchymal cells expresses fibroblast-specific protein (Fsp1), which is indicative of their shared properties with the migratory adult fibroblasts, and c-Fos, an oncogene associated with the down-regulation of epithelial cadherin.Both formation of the primitive streak and mesenchymal tissue is dependent on the Wnt/β-catenin pathway.