The key difference between desmosomes and hemidesmosomes is that the desmosomes directly form the cell to cell adhesions, while the hemidesmosomes form adhesions between cells and the basement membrane.
Cell to cell adhesions and cell junctions are important to maintain the integrity of a particular tissue and for enabling the cell to cell signalling mechanisms. There are different types of cellular adhesions in all species of higher-level eukaryotes. It is important to differentiate between different cellular adhesions to understand more about their biological mechanisms. Desmosomes and hemidesmosomes are two such cell adhesion structures discussed in this article.
CONTENTS
1. Overview and Key Difference
2. What are Desmosomes
3. What are Hemidesmosomes
4. Similarities Between Desmosomes and Hemidesmosomes
5. Side by Side Comparison – Desmosomes vs Hemidesmosomes in Tabular Form
6. Summary
What are Desmosomes?
Desmosomes, also known as macula adherens, are cell to cell adhesion structures. Their distribution is random in nature. However, they are mostly arranged around the lateral planes of the plasma membrane. Moreover, they are very strong in nature. Thus, desmosomes can resist high pressure and mechanical stress. Desmosomes are present in the junction points between cells of cardiac muscle, tissues of the bladder, the mucosal layer of the gastrointestinal tract and the epithelium.
Figure 01: Desmosome
Structurally, desmosomes are complex filamentous structures. They belong to the cell adhesion protein family: cadherin. Therefore, they contain proteins like desmoglein and desmocollin in their structure. They are highly rigid structures, and these proteins help to maintain their rigidity. The outer area of the desmosome forms a plaque that is highly dense in nature. They consist of desmoplakin in its structure.
Damages to desmosomes and mutations in desmosomes lead to conditions such as arrhythmogenic cardiomyopathy and a variety of autoimmune diseases.
What are Hemidesmosomes?
Hemidesmosomes are a type of cellular junction. They are small and stud-like structures, primarily found in the epidermis of the skin. Thus, most keratinocytes contain hemidesmosomes in between them. They are present in sites where the epidermis gets attached to the extracellular matrix. Thus, hemidesmosome is attached to two surfaces simultaneously. Hemidesmosome distribution is also seen in the epithelial cells. They form connections between the epithelial cells and the lamina lucida. Furthermore, hemidesmosomes are also involved in cell signalling pathways.
Figure 02: Hemidesmosome
There are two main types of hemidesmosomes as type I hemidesmosome and type II hemidesmosome. Type I hemidesmosomes are present in the stratified and pseudostratified epithelium. Type II hemidesmosomes contain integrin and plectin within them. Both these proteins are important in the formation of the association between keratin. Furthermore, hemidesmosomes also have many receptors in its outer membrane. It enables the cellular signalling mechanisms.
Thus, hemidesmosome damage may lead to the loosing of the integrity of the skin and leads to muscle dystrophy. Furthermore, mutations in the hemidesmosome expression can also lead to epidermolysis bullosa.
What are the Similarities Between Desmosomes and Hemidesmosomes?
- Desmosomes and hemidesmosomes are membrane-bound organelles.
- Moreover, both are round in shape.
- They are found in multicellular eukaryotes.
- Both are types of adhesion molecules.
- Functionally, they provide integrity to various tissues and organs.
- Both are important in acting as cell signalling molecules for signalling pathways.
What is the Difference Between Desmosomes and Hemidesmosomes?
The key difference between desmosomes and hemidesmosomes is the basis of their function. While desmosomes form cell to cell adhesions, hemidesmosomes form adhesions between cells and the basement membrane. Thus, the proteins involved in the structural functions vary between desmosomes and hemidesmosomes. Desmoglein and desmocollin are the proteins involved in desmosomes, while integrin and plectin are the proteins involved in hemidesmosomes.
The below infographic presents more information regarding the difference between desmosomes and hemidesmosomes.
Summary – Desmosomes vs Hemidesmosomes
Desmosomes and hemidesmosomes are membrane-bound structures that act as adhesion structures. Desmosomes act as cell to cell adhesions while hemidesmosomes act as adhesions that form between cells and the basement membrane. Thus, desmosomes are rigid junctions that are found in the cardiac muscle tissue or the gastrointestinal mucosa. In contrast, hemidesmosomes are primarily found in keratinocytes. Thus, they facilitate the adhesion of the keratinocytes to the basement membrane. So, this summarizes the difference between desmosomes and hemidesmosomes.
Reference:
1. Green, K J, and J C Jones. “Desmosomes and Hemidesmosomes: Structure and Function of Molecular Components.” FASEB Journal: Official Publication of the Federation of American Societies for Experimental Biology, U.S. National Library of Medicine, June 1996, Available here.
Image Courtesy:
1. “Desmosome – 2” By JWSchmidt at the English language Wikipedia (CC BY-SA 3.0) via Commons Wikimedia
2. “Hemidesmosomes showing interaction between integrins and laminin” By lu.qianhe – Own work (CC BY-SA 4.0) via Commons Wikimedia