Validity of Markers for Epithelial Cells and Mesenchymal Cells

Abstract

Stem cells are best known for their potential of differentiation. However, those so-called differentiated cells are not exactly lack of plasticity. This can be easily seen during wound healing, in which a lot of epithelial cells transform into fibroblasts or myofibroblasts to repair the tissue damage. Once the wound is healed, these cells can return to their original identity. This is commonly called epithelial-mesenchymal transition (EMT) or vice versa. Normally, these events are highly regulated and coordinated at the molecular level, so that tissues and organs can maintain their normal functions afterwards. However, when these processes are out of control due to various pathological reasons, adverse events like fibrosis can happen, or even worse, cancer cells can also take this advantage and become metastatic. Therefore, it is critical to identify these signs as early as possible, so that corrections can be made when it is necessary. Dozens of molecules have been used as markers to distinguish epithelial cells from mesenchymal cells, while emerging evidence questions their validity. The truth of the matter is each of these markers can be expressed in both groups at certain time point. EMT or vice versa is a progressive and highly dynamic process, and therefore, the molecular phenotype of a cell is volatile. It is the cumulative effect of all these so-called “markers” that finalize the cell identity, epithelial or mesenchymal.