An amicable separation: Chick's way of doing EMT.

Epithelial to mesenchymal transition (EMT) is a morphogenetic process in which cells lose their epithelial characteristics and gain mesenchymal properties, and is fundamental for many tissue remodeling events in developmental and pathological conditions. Although general cell biology of EMT has been well-described, how it is executed in diverse biological settings depends largely on individual context, and as a consequence, regulatory points for each EMT may vary. Here we discuss developmental and cellular events involved in chick gastrulation EMT. Regulated disruption of epithelial cell/basement membrane (BM) interaction is a critical early step. This takes place after molecular specification of mesoderm cell fate, but before the disruption of tight junctions. The epithelial cell/BM interaction is mediated by small GTPase RhoA and through the regulation of basal microtubule dynamics. We propose that EMT is not regulated as a single morphogenetic event. Components of EMT in different settings may share similar regulatory mechanisms, but the sequence of their execution and critical regulatory points vary for each EMT.