Epithelial or mesenchymal: Where to draw the line?

Area of Science:

• Cell Biology
• Molecular Biology
• Biochemistry

Background:

• Epithelial and mesenchymal cells are fundamental vertebrate cell types.
• Distinguishing between these cell types can be challenging due to unclear molecular distinctions.
• The validity of traditional cell markers is increasingly being questioned.

Purpose of the Study:

• To comprehensively compare the molecular phenotypes of epithelial and mesenchymal cells.
• To evaluate the reliability of commonly used molecular markers for cell typing.
• To investigate the impact of TGFbeta1 stimulation on marker expression in epithelial cells.

Main Methods:

• Quantitative PCR and immunofluorescence were employed.
• Six human and rat epithelial cell and fibroblast lines were analyzed.
• Twenty-two frequently used molecular markers were assessed.

Main Results:

• All tested "markers" showed expression in both epithelial and mesenchymal cells.
• Some "epithelial markers" (e.g., CLDN5, OCLN) were more highly expressed in fibroblasts.
• Mesenchymal markers exhibited higher fidelity, but some (e.g., CDH2, MMP9) were higher in epithelial cells.
• TGFbeta1 modulated the expression of specific epithelial and mesenchymal markers.

Conclusions:

• No single gene expression is strictly cell-type restricted.
• No universal markers consistently distinguish epithelial from mesenchymal cells across species.
• Certain molecules may serve as better, though not absolute, markers for specific cell types.
• Findings provide a reference for epithelial-mesenchymal transition, cell typing, and cancer diagnostics.