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Tonofibril

Tonofibrils are cytoplasmic protein structures in epithelial tissues that converge at desmosomes and hemidesmosomes. They consist of bundles of keratin intermediate filaments (tonofilaments) in epithelial cells that are anchored to the cytoskeleton. They were discovered by Rudolf Heidenhain, and first described in detail by Louis-Antoine Ranvier in 1897.

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Tonofibrils are cytoplasmic protein structures in epithelial tissues that converge at desmosomes and hemidesmosomes.1 They consist of bundles of keratin intermediate filaments (tonofilaments) in epithelial cells that are anchored to the cytoskeleton.23 They were discovered by Rudolf Heidenhain, and first described in detail by Louis-Antoine Ranvier in 1897.4

Composition

Tonofilaments are keratin intermediate filaments that make up tonofibrils in the epithelial tissue. They may also just be referred to as keratin intermediate filaments.5 In epithelial cells, tonofilaments loop through desmosomes. Electron microscopy has advanced now to illustrate the tonofilaments more clearly.1

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

The protein filaggrin is believed to be synthesized as a giant precursor protein, profilaggrin (>400 kDA in humans). When filaggrin binds to keratin intermediate filaments, the keratin aggregates into macrofibrils.3

References

References

  1. "tonofibril" at Dorland's Medical Dictionary
  2. "Keratinocytes". Kenhub. Retrieved 30 November 2025.
  3. Sandilands, Aileen; Sutherland, Calum; Irvine, Alan D.; McLean, W. H. Irwin (2009-05-01). "Filaggrin in the frontline: role in skin barrier function and disease". J Cell Sci. 122 (9): 1285–1294. doi:10.1242/jcs.033969. ISSN 0021-9533. PMC 2721001. PMID 19386895.
  4. Charles, Arwyn; Smiddy, F. G. (1957-09-01). "The Tonofibrils of the Human Epidermis1". Journal of Investigative Dermatology. 29 (5): 327–338. doi:10.1038/jid.1957.108. ISSN 0022-202X. PMID 13502588.
  5. Windoffer, R; Beil, M; Magin, TM; Leube, RE (5 September 2011). "Cytoskeleton in motion: the dynamics of keratin intermediate filaments in epithelia". The Journal of Cell Biology. 194 (5): 669–78. doi:10.1083/jcb.201008095. PMC 3171125. PMID 21893596.
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