Tonofibril

Tonofibrils are cytoplasmic protein structures found in epithelial cells. They are composed primarily of keratin intermediate filaments and are associated with cell adhesion structures such as desmosomes. Tonofibrils play a crucial role in maintaining the structural integrity and mechanical resilience of epithelial tissues.

Structure

Tonofibrils are bundles of intermediate filaments that are approximately 10 nm in diameter. These filaments are composed of keratin proteins, which are a type of fibrous protein. The keratin filaments are organized into a network that extends throughout the cytoplasm of epithelial cells, providing mechanical support and stability.

Function

The primary function of tonofibrils is to provide structural support to epithelial cells. They achieve this by forming a network that connects to desmosomes, which are specialized cell junctions that facilitate cell-cell adhesion. This connection helps distribute mechanical stress across the tissue, preventing damage and maintaining tissue integrity.

Tonofibrils also play a role in cellular signaling and the regulation of cell shape and motility. By interacting with other cytoskeletal elements, such as microtubules and actin filaments, tonofibrils contribute to the dynamic organization of the cytoskeleton.

Associated Structures

Desmosomes

Transmission electron micrograph of chiton epidermis showing tonofibrils.

Desmosomes are intercellular junctions that provide strong adhesion between epithelial cells. They are composed of desmosomal cadherins, such as desmogleins and desmocollins, which interact with the keratin filaments of tonofibrils. This interaction is crucial for the mechanical coupling of cells and the maintenance of tissue integrity.

Hemidesmosomes

Hemidesmosomes are similar to desmosomes but are involved in cell-matrix adhesion. They connect the basal surface of epithelial cells to the underlying basement membrane. Tonofibrils anchor to hemidesmosomes, providing additional stability to the epithelial layer.

Clinical Significance

Disruptions in tonofibril structure or function can lead to various skin disorders and diseases. For example, mutations in keratin genes can result in conditions such as epidermolysis bullosa, where the skin becomes fragile and prone to blistering. Understanding the role of tonofibrils in these conditions is important for developing therapeutic strategies.

Related Pages

• Intermediate filament
• Keratin
• Desmosome
• Epithelial tissue