Tonofibril

Tonofibrils are cytoplasmic protein structures in epithelial tissues that converge at desmosomes and hemidesmosomes.

[1] They consist of fine fibrils in epithelial cells that are anchored to the cytoskeleton.

[2] They were discovered by Rudolf Heidenhain, and first described in detail by Louis-Antoine Ranvier in 1897.

[3] Tonofilaments are keratin intermediate filaments that make up tonofibrils in the epithelial tissue.

In epithelial cells, tonofilaments loop through desmosomes.

Chiton epidermis TEM
Transmission electron micrograph depicting tonofilaments, labeled tf, running longitudinally within the dorsal epidermal cells of the girdle of a chiton