# Tonofibril

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**Tonofibrils** are cytoplasmic protein structures in [epithelial](/source/Epithelial) tissues that converge at [desmosomes](/source/Desmosomes) and [hemidesmosomes](/source/Hemidesmosomes).[1] They consist of bundles of keratin intermediate filaments (tonofilaments) in epithelial cells that are anchored to the [cytoskeleton](/source/Cytoskeleton).[2][3] They were discovered by [Rudolf Heidenhain](/source/Rudolf_Heidenhain), and first described in detail by [Louis-Antoine Ranvier](/source/Louis-Antoine_Ranvier) in 1897.[4]

## Composition

Tonofilaments are [keratin](/source/Keratin) [intermediate filaments](/source/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]

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

## References

1. [dead link]

1. ["Keratinocytes"](https://www.kenhub.com/en/library/anatomy/keratinocytes). *Kenhub*. Retrieved 30 November 2025.

1. 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](https://doi.org/10.1242/jcs.033969). [ISSN 0021-9533](https://www.worldcat.org/issn/0021-9533). [PMC 2721001](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2721001). [PMID 19386895](https://pubmed.ncbi.nlm.nih.gov/19386895)

1. 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](https://doi.org/10.1038/jid.1957.108). [ISSN 0022-202X](https://www.worldcat.org/issn/0022-202X). [PMID 13502588](https://pubmed.ncbi.nlm.nih.gov/13502588)

1. 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](https://doi.org/10.1083/jcb.201008095). [PMC 3171125](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3171125). [PMID 21893596](https://pubmed.ncbi.nlm.nih.gov/21893596)

## External links

- [Diagram at ultrakohl.com](https://web.archive.org/web/19990430043858/http://zappa.ultrakohl.com/EmOrganelle/organ10.htm)

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