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A temporary projection of the cytoplasm is referred to as a pseudopodium. They resemble an arm is filled with the cytoplasm and contains cytoskeleton filaments. The projections are primarily composed of actin filaments, microtubules, and intermediate filaments.
What is Pseudopodia?
The pseudopodia are formed by Amoeba and other amoeboid cells for locomotion and ingestion of food particles. The polymerization of actin filaments results in the formation of pseudopodia that push the cell membrane and form a temporary projection. These projections or pseudopodia are classified into lobopodia, filopodia, reticulopodia, axopodia, and lamellipodia.
The term pseudopodia are derived from a Greek word. The word is made up of two words pseudo + podos, the word pseudo means “false” and podos meaning “foot” or “leg”.
Amoeboid Cell Structure
The formation of pseudopodia generally takes place in amoeba or amoeboid cells. The structure of the amoeboid cell consists of two major regions: the endoplasm and the ectoplasm. The inner region is called the endoplasm that is granular whereas the outer region is clear, the ectoplasm is made up of actin filaments that make the region flexible and more contractile.
The actin filaments are relatively thinner than other cytoskeleton filaments and formed by polymerization through the aid of assembly proteins. Examples of assembly proteins include motor proteins, capping proteins, and branching proteins. The projections also consist of other cytoskeleton types such as microtubules, and intermediate filaments.
The intermediate filaments have a diameter of 8- 12 nm whereas microtubules are larger having a diameter of 25 nm. The actin filaments are the thinnest filaments among the three.
The pseudopodia are formed by the polymerization of actin proteins. A protrusive force by actin polymerization drive cell protrusion that results in the formation of chains and pushes the cell membrane in a particular direction. The formation of projection slides the rest of the cytoplasm forward by which the cell moves forward. This type of locomotion is referred to as amoeboid movement. Chemotaxis and the presence of chemical attractants determine the direction and formation of pseudopodia.
The example includes a chemical attractant that binds to a G-protein coupled receptor and results in the activation of signal transduction. The signal transduction finally activates the actin polymerization and form pseudopodium. A pseudopod that resembles the letter Y can be also formed by another pseudopod.
Types of Pseudopodia
The pseudopodia are classified into various types. For instance: Lobopodia, filopodia, reticulopodia, axopodia, and lamellipodia.
The finger-like, bulbous, bluntly rounded, tubular cytoplasmic projections are called lobopodia. This type of projection is commonly seen in the taxonomic group Lobosa and certain Amoebozoa and Excavata. they are the most common type of pseudopodia in nature.
They are slender, threadlike structures having pointed ends. The ectoplasm is the chief content in these types of pseudopodia. Examples include filose amoebae.
A reticular network form the projections called reticular pseudopodia. Examples of organisms having reticulating nets or reticulopodia are the reticulose amoebae and foraminiferans. Reticulopodia are chiefly used for food ingestion.
Axopodia are made up of thin cytoplasmic projections. They are narrow structures that contain a complex array of microtubules. Radiolarians consist of these types of pseudopodia that helps in phagocytosis and to stay buoyant.
They are broad and flat cytoplasmic projections. Example- Lecythium hyalinum, a testate amoeba.
The pseudopodia are mainly used for food ingestion, locomotion, buoyancy, and phagocytosis. The protozoans are also classified on the basis of different methods of cellular locomotion. They are divided into Sarcodina, Mastigophora, Ciliophora, and Sporozoa.
The members of class Sarcodina use pseudopodia for locomotion. Other members of protozoans use other projections such as cilia, flagella for the movement. Sarcodina uses pseudopodia and adopts amoeboid movement that is a crawling-like movement. Apart from the locomotion, pseudopodia also perform some other functions such as capturing prey and feeding.
The amoeboid cells are single-celled organisms that get nutrition from bacterial cells and detritus. They engulf the food particles with pseudopodia and convert them into food vacuoles. The WBC in humans can be likened to food ingestion. The WBC recognizes the foreign particle and engulfs it by its pseudopod that is later fused and digested within the lysosome.
Examples of pseudopodia-containing organisms are amoeboid cells and Amoeba. They move and engulf food with the help of these cytoplasmic projections. Apart from the genus Amoeba, some other members of the kingdom protists also use pseudopods.
The examples are genera Entamoeba and Naegleria. Both of them are medically important and cause diseases in humans. The disease, amoebic dysentery is caused by Entamoeba histolytica whereas Naegleria fowleri is also known as brain-eating amoeba.
White blood cells in humans also contain pseudopodia that help to engulf foreign particles or antigens. The human mesenchymal cells are also an example of pseudopodia-containing cells.
- Filopodia: molecular architecture and cellular functions. Nat Rev Mol Cell Biol . 2008 Jun;9(6):446-54.
- Filopodia in cell adhesion, 3D migration and cancer cell invasion. Curr Opin Cell Biol . 2015 Oct;36:23-31.
- Guiding cell migration through directed extension and stabilization of pseudopodia. Exp Cell Res . 2004 Nov 15;301(1):31-7.