EMT in developmental morphogenesis

Carcinomas, cancers of epithelial origin, constitute the majority of all cancers. Loss of epithelial characteristics is an early step in carcinoma progression. Malignant transformation and metastasis involve additional loss of cell-cycle control and gain of migratory behaviors. Understanding the relationships among epithelial homeostasis, cell proliferation, and cell migration is therefore fundamental in understanding cancer. Interestingly, these cellular events also occur frequently during animal development, but without leading to tumor formation. Can we learn anything about carcinomas from developmental biology? In this review, we focus on one aspect of carcinoma progression, the Epithelial-Mesenchymal Transition (EMT), and provide an overview of how the EMT is involved in normal amniote development. We discuss 12 developmental and morphogenetic processes that clearly involve the EMT. We conclude by emphasizing the diversity of EMT processes both in terms of their developmental context and of their cellular morphogenesis. We propose that there is comparable diversity in cancer microenvironment and molecular regulation of cancer EMTs.