Analysis of epithelial-to-mesenchymal transition (EMT). (a) It is proposed that in EMT the myofibroblasts in liver fibrosis originate from hepatic epithelial cells, consisting of hepatocytes (albumin+ [Alb+] cells), cholangiocytes (cytokeratin-19+ [K19+] cells), or progenitor cells (AFP+ cells). (b) Determining the origin of myofibroblasts using cell fate mapping. If a cell expressed α-fetoprotein (AFP), it will be irreversibly genetically labeled. AFP-driven Cre labeled epithelial progenitor cells, cholangiocytes, and hepatocytes, but failed to label any hepatic stellate cells (HSCs) or myofibroblasts. YFP, yellow fluorescent protein.41