Role of the epithelial-mesenchymal transition and its effects on embryonic stem cells.

The epithelial-mesenchymal transition (EMT) is important for embryonic development and the formation of various tissues or organs. However, EMT dysfunction in normal cells leads to diseases, such as cancer or fibrosis. During the EMT, epithelial cells are converted into more invasive and active mesenchymal cells. E-box-binding proteins, including Snail, ZEB and helix-loop-helix family members, serve as EMT-activating transcription factors. These transcription factors repress the expression of epithelial markers, for example, E-cadherin, rearrange the cytoskeleton and promote the expression of mesenchymal markers, such as vimentin, fibronectin and other EMT-activating transcription factors. Signaling pathways that induce EMT, including transforming growth factor-β, Wnt/glycogen synthase kinase-3β, Notch and receptor tyrosine kinase signaling pathways, interact with each other for the regulation of this process. Although the mechanism(s) underlying EMT in cancer or embryonic development have been identified, the mechanism(s) in embryonic stem cells (ESCs) remain unclear. In this review, we describe the underlying mechanisms of important EMT factors, indicating a precise role for EMT in ESCs, and characterize the relationship between EMT and ESCs.