Difference Between Tonofibrils and Tonofilaments

The key difference between tonofibrils and tonofilaments is that tonofibrils are cytoplasmic fibrils found in epithelial cells that converge at desmosomes and hemidesmosomes, providing a framework to the cell while tonofilaments are keratin intermediate filaments that combine as bundles to make tonofibrils.

Intermediate filaments are cytoplasmic protein structures found in eukaryotic cells. These filaments are essential for maintaining cell structure. They provide tensile strength to the cell. Intermediate filaments in epithelial cells are made from keratin protein. Tonofilaments are keratin intermediate filaments found in epithelial cells. Bundles of tonofilaments form a tonofibril. Therefore, tonofibrils are composed of tonofilaments made from 8 keratin intermediate filaments.

CONTENTS

1. Overview and Key Difference
2. What are Tonofibrils 
3. What are Tonofilaments
4. Similarities Between Tonofibrils and Tonofilaments
5. Side by Side Comparison – Tonofibrils vs Tonofilaments in Tabular Form
6. Summary

What are Tonofibrils?

Desmosomes are thickened cellular areas on the plasma membrane of adjacent epithelial cells which mediate cell to cell adhesion. These are specialized structures of animal cells. There are fibrils in the cytoplasmic side of the desmosomes. These fibrils are known as tonofibrils. They are cytoplasmic protein structures that radiate from the cytoplasm and are anchored to the cytoskeleton. Rudolf Heidenhain discovered tonofibrils.

Tonofibrils are composed of keratin intermediate filaments called tonofilaments. In other words, tonofilaments combine to form thicker tonofibrils. Structurally, tonofibrils are made up of tonofilaments made from 8 keratin intermediate filaments. Tonofibrils are visible bundles of keratin filaments. They provide resistance to abrasion.

What are Tonofilaments?

Tonofilaments are intermediate filaments found in the cytoplasm of epithelial cells. Tonofilaments are well developed in the epidermis. They are made from a variable number of related proteins; keratin protein. They are approximately 0.7–0.8 nm in diameter. Bundles of tonofilaments together form a tonofibril. Tonofilaments are conspicuous in areas just beneath desmosomal plaques. They help in anchoring to the cytoplasm.

Tonofilaments interact with the intracellular attachment proteins in the plaques on the inner surface of cells joined by desmosomes. Tonofilaments loop through desmosomes. Moreover, hemidesmosomes also interact with tonofilament intermediate filaments.

What are the Similarities Between Tonofibrils and Tonofilaments?

• Tonofilaments and tonofibrils are found in desmosomes between epithelial cells.
• Both are composed of proteins, especially from structural protein keratin.
• In fact, they are cytoplasmic protein structures.
• Bundles of tonofilaments make tonofibrils.
• They are involved in the organization of eukaryotic cell cytoplasm.
• Moreover, they help to anchor to the cell cytoplasm.
• Both tonofilament and tonofibrils are the aggregations of filaments.

What is the Difference Between Tonofibrils and Tonofilaments?

Tonofibrils are protein fibrils found in the cytoplasmic side of desmosomes between epithelial cells. Tonofilaments are keratinous intermediate filaments that combine into bundles to form tonofibrils. So, this is the key difference between tonofibrils and tonofilaments. Structurally, tonofibrils are bundles of tonofilaments while tonofilaments are composed of 8 intermediate keratin filaments K5 and K14. Thus, this is the structural difference between tonofibrils and tonofilaments. Moreover, tonofibrils and tonofilaments are attached to the inner membrane of the desmosomes. Tonofibrils are thicker than tonofilaments and tonofilaments are approximately 0.7–0.8 nm in diameter. Thus, this is another difference between tonofibrils and tonofilaments.

Summary – Tonofibrils vs Tonofilaments

Tonofibrils are made up of bundles of keratinous intermediate filaments called tonofilaments. Tonofilaments are composed of the intermediate keratin filaments K5 and K14, Both tonofilaments and tonofibrils are components of the cytoskeleton of animal cells. They are found in desmosomes between epithelial cells.  They are attached to the inner membrane of the desmosomes. Tonofibrils support cell to cell adhesion and provide resistance to abrasion. Tonofilaments interact with other intracellular attachment proteins found in desmosomes. Thus, this summarizes the difference between tonofibrils and tonofilaments.

Reference:

1. “Tonofibril.” Wikipedia, Wikimedia Foundation, 3 Dec. 2019, Available here.
2. Brody, I.., et al. “An Electron Microscopic Study of the Human Epidermal Keratinocyte.” Cell and Tissue Research, Springer-Verlag, Available here.

Image Courtesy:

1. “Desmosome cell junction en” By Mariana Ruiz LadyofHats – Own work (Public Domain) via Commons Wikimedia
2. “Hemidesmosomes showing interaction between integrins and laminin” By lu.qianhe – Own work (CC BY-SA 4.0) via Commons Wikimedia