Urothelial plaque formation in post-Golgi compartments

Area of Science:

• Cell Biology
• Membrane Biology
• Urothelial Cell Function

Background:

• Urothelial plaques are specialized membrane domains in superficial umbrella cells.
• These plaques are crucial for the barrier function of the urothelium.
• The biogenesis and transport pathway of urothelial plaques remain incompletely understood.

Purpose of the Study:

• To investigate the membrane compartments involved in the formation of urothelial plaques in mouse umbrella cells.
• To elucidate the step-by-step process of de novo urothelial plaque biogenesis.
• To characterize the role of post-Golgi vesicles in plaque assembly.

Main Methods:

• Immunofluorescence labeling with anti-uroplakin antibodies.
• Characterization of membrane compartments in mouse umbrella cells using electron microscopy.
• Analysis of vesicle morphology and uroplakin distribution.

Main Results:

• Three distinct post-Golgi compartments containing uroplakins were identified: uroplakin-positive transporting vesicles (UPTVs), immature fusiform vesicles (iFVs), and mature fusiform vesicles (mFVs).
• UPTVs carry individual uroplakin particles, fuse to form iFVs where plaques begin to assemble, and iFVs mature into mFVs containing large plaques.
• Endocytic markers were absent in these plaque-forming compartments, suggesting a de novo formation pathway.

Conclusions:

• A detailed model for de novo urothelial plaque formation is proposed, originating from the Golgi apparatus via UPTVs, iFVs, and mFVs.
• This pathway involves the sequential concentration of uroplakins and maturation of vesicles to form functional plaques.
• The findings provide new insights into the biogenesis of specialized membrane domains in urothelial cells.