Microridges

Microridges are microscopic ridge-like protrusions on the apical surface of certain squamous epithelial cells, most prominently in the epidermis of fish and amphibian larvae. Under light and electron microscopy, they form a labyrinthine pattern of ridges that run in longitudinal or intersecting directions across the cell surface.

Structure and organization: Each microridge is built from an underlying network of actin filaments just beneath the apical plasma membrane. The actin cortex supports elongated ridges and is organized into a patterned array, producing a stable yet dynamic surface topography that differs from simple microvilli. The ridges can form intricate, maze-like arrangements rather than uniform rows.

Function and development: The ridges increase the effective surface area of the epithelium and help retain a mucus or mucopolysaccharide layer, aiding hydration, lubrication, and protection against drying and minor mechanical stress. They may influence surface wetting and barrier properties. Microridges arise during embryonic stages in fish and amphibians and can remodel as tissues grow or respond to environmental factors. They are frequently studied as a model of actin-based membrane protrusions and epithelial surface patterning.