Pseudopodia

A pseudopod or pseudopodium (plural: pseudopods or pseudopodia) (from the Greek word ψευδοποδός, ψευδός 'false' + ποδός 'foot') is a temporary arm-like projection of a eukaryotic cell membrane. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and may also contain microtubules and intermediate filaments. Pseudopods are used for motility and ingestion. They are often found in amoebas. A pseudopod or pseudopodium (plural: pseudopods or pseudopodia) (from the Greek word ψευδοποδός, ψευδός 'false' + ποδός 'foot') is a temporary arm-like projection of a eukaryotic cell membrane. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and may also contain microtubules and intermediate filaments. Pseudopods are used for motility and ingestion. They are often found in amoebas. Different types of pseudopodia can be classified by their distinct appearances. Lamellipodia are broad and thin. Filopodia are slender, thread-like, and are supported largely by microfilaments. Lobopodia are bulbous and amoebic. Reticulopodia are complex structures bearing individual pseudopodia which form irregular nets. Axopodia are the phagocytosis type with long, thin pseudopods supported by complex microtubule arrays enveloped with cytoplasm; they respond rapidly to physical contact. However some pseudopodial cells are able to use multiple types of pseudopodia depending on the situation: Most of them use a combination of lamellipodia and filopodia to migrate (e.g. metastatic cancer cells). The human foreskin fibroblasts can either use lamellipodia- or lobopodia-based migration in a 3D matrix depending on the matrix elasticity. Generally, several pseudopodia arise from the surface of the body, (polypodial, e.g. Amoeba proteus), or a single pseudopod may form on the surface of the body (monopodial, e.g. Entamoeba histolytica). Cells which make pseudopods are generally referred to as amoeboids. To move towards a target, the cell uses chemotaxis. It senses extracellular signalling molecules, chemoattractants (e.g. cAMP for Dictyostelium cells), to extend pseudopodia at the membrane area facing the source of these molecules. The chemoattractants bind to G protein-coupled receptors, which activate GTPases of the Rho family (e.g. Cdc42, Rac) via G-proteins. Rho GTPases are able to activate WASp which in turn activate Arp2/3 complex which serve as nucleation sites for actin polymerization. The actin polymers then push the membrane as they grow, forming the pseudopod. The pseudopodium can then adhere to a surface via its adhesion proteins (e.g. integrins), and then pull the cell's body forward via contraction of an actin-myosin complex in the pseudopod. This type of locomotion is called Amoeboid movement. Rho GTPases can also activate phosphatidylinositol 3-kinase (PI3K) which recruit PIP3 to the membrane at the leading edge and detach the PIP3-degrading enzyme PTEN from the same area of the membrane. PIP3 then activate GTPases back via GEF stimulation. This serves as a feedback loop to amplify and maintain the presence of local GTPase at the leading edge.