Microfilament-rich cells in the toad bladder epithelium

Area of Science:

• Comparative physiology
• Cell biology
• Urothelial research

Background:

• The basal layer of the bladder epithelium is crucial for urothelial maintenance and regeneration.
• Heterogeneity within basal cell populations can influence tissue function and response to stimuli.
• Previous studies have not fully characterized the distinct cell types within the basal layer of amphibian bladders.

Purpose of the Study:

• To investigate the heterogeneity of basal cells in the Bufo marinus bladder epithelium.
• To identify and characterize microfilament-rich cells (MFR-cells) and undifferentiated cells (Un-cells).
• To determine the proliferative potential and potential functions of these distinct basal cell types.

Main Methods:

• Electron microscopy to examine cell morphology and ultrastructure.
• Immunofluorescence staining for actin to identify MFR-cells.
• 3H-thymidine pulse labeling and autoradiography to assess cell proliferation.
• Isopycnic centrifugation for cell separation and density analysis.

Main Results:

• Two distinct basal cell types identified: microfilament-rich cells (MFR-cells, ~20%) and undifferentiated cells (Un-cells).
• MFR-cells possess abundant intermediate filaments, contact adjacent cells via desmosomes, and show strong actin immunofluorescence.
• Un-cells lack specialized organelles and intercellular contacts, with cytoplasm rich in free ribosomes.
• Proliferation analysis revealed that ~10% of undifferentiated basal cells incorporated 3H-thymidine, while MFR-cells and granular cells showed minimal to no incorporation.
• MFR-cells exhibit a distinct buoyant density and co-sediment with mitochondria-rich cells.

Conclusions:

• The basal bladder epithelium of Bufo marinus is heterogeneous, comprising MFR-cells and Un-cells with distinct ultrastructural and proliferative characteristics.
• MFR-cells, characterized by actin and intermediate filaments, appear to be non-proliferative and may be involved in cell coupling or signaling.
• Undifferentiated cells represent the proliferative basal cell population, contributing to urothelial turnover.