A dominant mutant of occludin disrupts tight junction structure and function

Area of Science:

• Cell Biology
• Epithelial Biology
• Membrane Proteins

Background:

• Tight junctions form essential diffusion barriers in epithelial cells.
• Occludin is a key integral membrane protein localized to tight junctions.
• The precise role of occludin in tight junction regulation remains to be fully elucidated.

Purpose of the Study:

• To investigate the function of occludin in tight junction assembly and barrier integrity.
• To determine the specific domains of occludin critical for its role.

Main Methods:

• Stable transfection of murine epithelial cells (CSG 120/7) with full-length and N-terminally truncated FLAG-tagged occludin constructs.
• Assessment of tight junction localization via colocalization with ZO-1.
• Measurement of cell monolayer permeability using transcellular electrical resistance and paracellular flux assays.
• Visualization of tight junction strand morphology using freeze-fracture electron microscopy.

Main Results:

• Both full-length and truncated occludin constructs correctly localized to tight junctions.
• The occludin construct lacking N-terminal and extracellular domains severely disrupted tight junction integrity.
• Impaired barrier function was evidenced by reduced electrical resistance and increased tracer flux.
• Freeze-fracture electron microscopy revealed gaps in tight junction strands.

Conclusions:

• The N-terminal half of occludin plays a vital role in the assembly and maintenance of tight junction barrier function.
• Specific domains of occludin are essential for establishing and preserving epithelial cell sealing.
• These findings highlight occludin as a critical regulator of epithelial paracellular permeability.