Pseudopodium
   HOME

TheInfoList



OR:

A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a
eukaryotic The eukaryotes ( ) constitute the Domain (biology), domain of Eukaryota or Eukarya, organisms whose Cell (biology), cells have a membrane-bound cell nucleus, nucleus. All animals, plants, Fungus, fungi, seaweeds, and many unicellular organisms ...
cell membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
that is emerged in the direction of movement. Filled with
cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
, pseudopodia primarily consist of
actin filaments Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other p ...
and may also contain
microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...
s and
intermediate filament Intermediate filaments (IFs) are cytoskeleton, cytoskeletal structural components found in the cells of vertebrates, and many invertebrates. Homologues of the IF protein have been noted in an invertebrate, the cephalochordate ''Branchiostoma' ...
s. Pseudopods are used for
motility Motility is the ability of an organism to move independently using metabolism, metabolic energy. This biological concept encompasses movement at various levels, from whole organisms to cells and subcellular components. Motility is observed in ...
and
ingestion Ingestion is the consumption of a substance by an organism. In animals, it normally is accomplished by taking in a substance through the mouth into the gastrointestinal tract, such as through eating or drinking. In single-celled organisms, inge ...
. They are often found in
amoeba An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of Cell (biology), cell or unicellular organism with the ability to alter its shape, primarily by ...
s. Different types of pseudopodia can be classified by their distinct appearances.
Lamellipodia The lamellipodium (: lamellipodia) (from Latin ''lamella'', related to ', "thin sheet", and the Greek radical ''pod-'', "foot") is a cytoskeletal protein actin projection on the leading edge of the cell. It contains a quasi-two-dimensional act ...
are broad and thin.
Filopodia Filopodia (: filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as ''microspikes'', and when they extend beyond the lamellipod ...
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 A pseudopod or pseudopodium (: pseudopods or pseudopodia) is a temporary arm-like projection of a eukaryotic cell membrane that is emerged in the direction of movement. Filled with cytoplasm, pseudopodia primarily consist of actin filaments and ...
are the
phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
type with long, thin pseudopods supported by complex microtubule arrays enveloped with cytoplasm; they respond rapidly to physical contact. Generally, several pseudopodia arise from the surface of the body, (''polypodial'', for example, ''
Amoeba proteus ''Amoeba proteus'' is a large species of amoeba closely related to another genus of giant amoebae, ''Chaos (genus), Chaos''. As such, the species is sometimes given the alternative scientific name ''Chaos diffluens''. This protozoan uses extensi ...
''), or a single pseudopod may form on the surface of the body (''monopodial'', such as ''
Entamoeba histolytica ''Entamoeba histolytica'' is an anaerobic organism, anaerobic parasitic amoebozoan, part of the genus ''Entamoeba''. Predominantly infecting humans and other primates causing amoebiasis, ''E. histolytica'' is estimated to infect about 35-50 mil ...
'').


Formation

Cells which make pseudopods are generally referred to as ''
amoeboids An amoeba (; less commonly spelled ameba or amœba; : amoebas (less commonly, amebas) or amoebae (amebae) ), often called an amoeboid, is a type of cell or unicellular organism with the ability to alter its shape, primarily by extending and r ...
''.


Via extracellular cue

To move towards a target, the cell uses
chemotaxis Chemotaxis (from ''chemical substance, chemo-'' + ''taxis'') is the movement of an organism or entity in response to a chemical stimulus. Somatic cells, bacteria, and other single-cell organism, single-cell or multicellular organisms direct thei ...
. It senses extracellular signalling molecules, chemoattractants (e.g. cAMP for ''
Dictyostelium ''Dictyostelium'' is a genus of single- and multi-celled eukaryotic, phagotrophic bacterivores. Though they are Protista and in no way fungal, they traditionally are known as "slime molds". They are present in most terrestrial ecosystems a ...
'' cells), to extend pseudopodia at the membrane area facing the source of these molecules. The chemoattractants bind to
G protein-coupled receptor G protein-coupled receptors (GPCRs), also known as seven-(pass)-transmembrane domain receptors, 7TM receptors, heptahelical receptors, serpentine receptors, and G protein-linked receptors (GPLR), form a large group of evolutionarily related ...
s, which activate GTPases of the Rho family (e.g. Cdc42, Rac) via
G protein G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their ac ...
s. Rho GTPases are able to activate
WASp A wasp is any insect of the narrow-waisted suborder Apocrita of the order Hymenoptera which is neither a bee nor an ant; this excludes the broad-waisted sawflies (Symphyta), which look somewhat like wasps, but are in a separate suborder ...
which in turn activate
Arp2/3 complex Arp2/3 complex (Actin Related Protein 2/3 complex) is a seven-subunit protein complex that plays a major role in the regulation of the actin cytoskeleton. It is a major component of the actin cytoskeleton and is found in most actin cytoskeleton ...
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.
integrin Integrins are transmembrane receptors that help cell–cell and cell–extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, o ...
s), 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 Amoeboid movement is the most typical mode of locomotion in adherent eukaryotic cells. It is a crawling-like type of movement accomplished by protrusion of cytoplasm of the cell involving the formation of pseudopodia ("false-feet") and posterio ...
''. Rho GTPases can also activate
phosphatidylinositol 3-kinase Phosphoinositide 3-kinases (PI3Ks), also called phosphatidylinositol 3-kinases, are a family of enzymes involved in cellular functions such as cell growth, proliferation, differentiation, motility, survival and intracellular trafficking, which i ...
(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. Otherwise, pseudopodia cannot grow on other sides of the membrane than the leading edge because myosin filaments prevent them to extend. These myosin filaments are induced by
cyclic GMP Cyclic guanosine monophosphate (cGMP) is a cyclic nucleotide derived from guanosine triphosphate (GTP). cGMP acts as a second messenger much like cyclic AMP. Its most likely mechanism of action is activation of intracellular protein kinases in res ...
in '' D. discoideum'' or
Rho kinase Rho-associated protein kinase or Rho-associated coiled-coil kinase (ROCK) is a kinase belonging to the AGC (PKA/ PKG/PKC) family of serine-threonine specific protein kinases. It is involved mainly in regulating the shape and movement of cells by ...
in
neutrophil Neutrophils are a type of phagocytic white blood cell and part of innate immunity. More specifically, they form the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. Their functions vary in differe ...
s for example. Different physical parameters were shown to regulate the length and time-scale of pseudopodia formation. For example, an increase in membrane tension inhibits actin assembly and protrusion formation. It was demonstrated that the lowered negative
surface charge A surface charge is an electric charge present on a two-dimensional surface. These electric charges are constrained on this 2-D surface, and surface charge density, measured in coulombs per square meter (C•m−2), is used to describe the charge ...
on the inner surface of the
plasma membrane The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extr ...
generates protrusions via activation of the Ras- PI3K/AKT/mTOR signalling pathway.


Without extracellular cue

In the case there is no extracellular cue, all moving cells navigate in random directions, but they can keep the same direction for some time before turning. This feature allows cells to explore large areas for colonization or searching for a new extracellular cue. In ''Dictyostelium'' cells, a pseudopodium can form either ''de novo'' as normal, or from an existing pseudopod, forming a Y-shaped pseudopodium. The Y-shaped pseudopods are used by ''Dictyostelium'' to advance relatively straight forward by alternating between retraction of the left or right branch of the pseudopod. The ''de novo'' pseudopodia form at different sides than pre-existing ones, they are used by the cells to turn. Y-shaped pseudopods are more frequent than ''de novo'' ones, which explain the preference of the cell to keep moving to the same direction. This persistence is modulated by PLA2 and cGMP signalling pathways.


Functions

The functions of pseudopodia include locomotion and ingestion: * Pseudopodia are critical in sensing targets which can then be engulfed; the engulfing pseudopodia are called
phagocytosis Phagocytosis () is the process by which a cell (biology), cell uses its plasma membrane to engulf a large particle (≥ 0.5 μm), giving rise to an internal compartment called the phagosome. It is one type of endocytosis. A cell that performs ph ...
pseudopodia. A common example of this type of amoeboid cell is the
macrophage Macrophages (; abbreviated MPhi, φ, MΦ or MP) are a type of white blood cell of the innate immune system that engulf and digest pathogens, such as cancer cells, microbes, cellular debris and foreign substances, which do not have proteins that ...
. * They are also essential to amoeboid-like locomotion. Human
mesenchymal stem cell Mesenchymal stem cells (MSCs), also known as mesenchymal stromal cells or medicinal signaling cells, are multipotent stromal cells that can Cellular differentiation, differentiate into a variety of cell types, including osteoblasts (bone cells), ...
s are a good example of this function: these migratory cells are responsible for in-utero remodeling; for example, in the formation of the
trilaminar germ disc A trilaminar embryonic disc, trilaminary blastoderm, or trilaminar germ disk is an early stage in the development of triploblastic organisms, which include humans and many other animals. It is the next stage from the earlier bilaminar embryonic dis ...
during
gastrulation Gastrulation is the stage in the early embryonic development of most animals, during which the blastula (a single-layered hollow sphere of cells), or in mammals, the blastocyst, is reorganized into a two-layered or three-layered embryo known as ...
.


Morphology

Pseudopods can be classified into several varieties according to the number of projections (monopodia and polypodia), and according to their appearance. Some pseudopodial cells are able to use multiple types of pseudopodia depending on the situation. Most use a combination of
lamellipodia The lamellipodium (: lamellipodia) (from Latin ''lamella'', related to ', "thin sheet", and the Greek radical ''pod-'', "foot") is a cytoskeletal protein actin projection on the leading edge of the cell. It contains a quasi-two-dimensional act ...
and
filopodia Filopodia (: filopodium) are slender cytoplasmic projections that extend beyond the leading edge of lamellipodia in migrating cells. Within the lamellipodium, actin ribs are known as ''microspikes'', and when they extend beyond the lamellipod ...
to migrate (e.g. metastatic cancer cells). Human
foreskin In male Human body, human anatomy, the foreskin, also known as the prepuce (), is the double-layered fold of Human skin, skin, Mucous membrane, mucosal and Muscle tissue, muscular tissue at the distal end of the human penis that covers the glans ...
fibroblasts can either use lamellipodia- or lobopodia-based migration in a 3D matrix depending on the matrix elasticity.


Lamellipodia

Lamellipodia are broad and flat pseudopodia used in locomotion. They are supported by microfilaments which form at the leading edge, creating a mesh-like internal network.


Filopodia

Filopodia (or filose pseudopods) are slender and filiform with pointed ends, consisting mainly of ectoplasm. These formations are supported by
microfilament Microfilaments, also called actin filaments, are protein filaments in the cytoplasm of eukaryotic cells that form part of the cytoskeleton. They are primarily composed of polymers of actin, but are modified by and interact with numerous other ...
s which, unlike the filaments of lamellipodia with their net-like actin, form loose bundles by
cross-link In chemistry and biology, a cross-link is a bond or a short sequence of bonds that links one polymer chain to another. These links may take the form of covalent bonds or ionic bonds and the polymers can be either synthetic polymers or natural ...
ing. This formation is partly due to bundling proteins such as
fimbrin Fimbrin also known as is plastin 1 is a protein that in humans is encoded by the PLS1 gene. Fimbrin is an actin cross-linking protein important in the formation of filopodia. Structure Fimbrin belongs to the calponin homology (CH) domain sup ...
s and
fascin Fascin is an actin bundling protein. Species and tissue distribution It is a 54–58 kilodalton monomeric actin filament bundling protein originally isolated from sea urchin egg but also found in ''Drosophila'' and vertebrates, includi ...
s. Filopodia are observed in some animal cells: in part of
Filosa Cercozoa (now synonymised with Filosa) is a phylum of diverse single-celled eukaryotes. They lack shared morphological characteristics at the microscopic level, and are instead united by phylogeny, molecular phylogenies of rRNA and actin or Ubiqu ...
(
Rhizaria The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus '' Paulinella'' in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera ...
), in " Testaceafilosia", in
Vampyrellidae The family Vampyrellidae is a subgroup of the order Vampyrellida (or Aconchulinida) within the supergroup Rhizaria. Based on molecular sequence data, the family currently comprises the genus '' Vampyrella'', and maybe several other vampyrelli ...
and Pseudosporida (
Rhizaria The Rhizaria are a diverse and species-rich clade of mostly unicellular eukaryotes. Except for the Chlorarachniophytes and three species in the genus '' Paulinella'' in the phylum Cercozoa, they are all non-photosynthetic, but many Foraminifera ...
) and in
Nucleariida The nucleariids, or nucleariid amoebae, are a group of amoebae that compose the sister clade of the fungi. Together, they form the clade Holomycota. They are aquatic organisms found in freshwater and marine habitats, as well as in faeces. They a ...
( Opisthokonta).


Lobopodia

Lobopodia (or lobose pseudopods) are bulbous, short, and blunt in form. These finger-like, tubular pseudopodia contain both ectoplasm and
endoplasm Endoplasm, also known as entoplasm, generally refers to the inner (often granulated), dense part of a cell's cytoplasm. This is opposed to the ectoplasm (cell biology), ectoplasm which is the outer (non-granulated) layer of the cytoplasm, which ...
. They can be found in different kind of cells, notably in
Lobosa Lobosa is a taxonomic group of amoebae in the phylum Amoebozoa. Most lobosans possess broad, bluntly rounded pseudopods, although one genus in the group, the recently discovered ''Sapocribrum,'' has slender and threadlike (filose) pseudopodia. ...
and other
Amoebozoa Amoebozoa is a major Taxonomy (biology), taxonomic group containing about 2,400 described species of Amoeba, amoeboid protists, often possessing blunt, fingerlike, Pseudopod#Morphology, lobose pseudopods and tubular mitochondrial cristae. In trad ...
and in some
Heterolobosea Heterolobosea are a class of Percolozoa. The only member of this class that is infectious to humans is '' Naegleria fowleri'', the causative agent of the often fatal disease amoebic meningitis. Typically, their life cycle alternates between fl ...
(
Excavata Excavata is an obsolete, extensive and diverse paraphyletic group of unicellular Eukaryota. The group was first suggested by Simpson and Patterson in 1999 and the name latinized and assigned a rank by Thomas Cavalier-Smith in 2002. It contains ...
). High-pressure lobopodia can also be found in human
fibroblast A fibroblast is a type of cell (biology), biological cell typically with a spindle shape that synthesizes the extracellular matrix and collagen, produces the structural framework (Stroma (tissue), stroma) for animal Tissue (biology), tissues, and ...
s travelling through a complex network of 3D
matrix Matrix (: matrices or matrixes) or MATRIX may refer to: Science and mathematics * Matrix (mathematics), a rectangular array of numbers, symbols or expressions * Matrix (logic), part of a formula in prenex normal form * Matrix (biology), the m ...
(e.g. mammalian
dermis The dermis or corium is a layer of skin between the epidermis (skin), epidermis (with which it makes up the cutis (anatomy), cutis) and subcutaneous tissues, that primarily consists of dense irregular connective tissue and cushions the body from s ...
, cell-derived matrix). Contrarily to other pseudopodia using the pressure exerted by actin polymerization on the membrane to extend, fibroblast lobopods use the nuclear piston mechanism consisting in pulling the nucleus via actomyosin contractility to push the
cytoplasm The cytoplasm describes all the material within a eukaryotic or prokaryotic cell, enclosed by the cell membrane, including the organelles and excluding the nucleus in eukaryotic cells. The material inside the nucleus of a eukaryotic cell a ...
that in turn push the membrane, leading to pseudopod formation. To occur, this lobopodia-based fibroblast migration needs nesprin 3,
integrin Integrins are transmembrane receptors that help cell–cell and cell–extracellular matrix (ECM) adhesion. Upon ligand binding, integrins activate signal transduction pathways that mediate cellular signals such as regulation of the cell cycle, o ...
s,
RhoA Transforming protein RhoA, also known as Ras homolog family member A (RhoA), is a small GTPase protein in the Rho family of GTPases that in humans is encoded by the ''RHOA'' gene. While the effects of RhoA activity are not all well known, it is ...
,
ROCK Rock most often refers to: * Rock (geology), a naturally occurring solid aggregate of minerals or mineraloids * Rock music, a genre of popular music Rock or Rocks may also refer to: Places United Kingdom * Rock, Caerphilly, a location in Wale ...
and
myosin II Myosins () are a family of motor proteins (though most often protein complexes) best known for their roles in muscle contraction and in a wide range of other motility processes in eukaryotes. They are ATP-dependent and responsible for actin-ba ...
. Otherwise, lobopods are often accompanied with small lateral blebs forming along the side of the cell, probably due to the high intracellular pressure during lobopodia formation increasing the frequency of plasma membrane-cortex rupture.


Reticulopodia

Reticulopodia (or reticulose pseudopods), are complex formations in which individual pseudopods are merged and form irregular nets. The primary function of reticulopodia, also known as myxopodia, is food ingestion, with locomotion a secondary function. Reticulopods are typical of
Foraminifera Foraminifera ( ; Latin for "hole bearers"; informally called "forams") are unicellular organism, single-celled organisms, members of a phylum or class (biology), class of Rhizarian protists characterized by streaming granular Ectoplasm (cell bio ...
,
Chlorarachnea The chlorarachniophytes are a small group of exclusively marine algae widely distributed in tropical and temperate waters. They are typically mixotrophic, ingesting bacteria and smaller protists as well as conducting photosynthesis. Normally the ...
, ''
Gromia ''Gromia'' is a genus of protists, closely related to foraminifera, which inhabit marine and freshwater environments. It is the only genus of the family Gromiidae. ''Gromia'' are ameboid, producing filose pseudopodia that extend out from the cel ...
'' and ''
Filoreta Reticulosida is an order of Endomyxa that was created by Cavalier-Smith in 2003, but subsequently emended in by Bass et al. in 2009 to include only one monotypic In biology, a monotypic taxon is a taxonomic group (taxon) that contains only o ...
'' (Rhizaria).


Axopodia

Axopodia (also known as actinopodia) are narrow pseudopodia containing complex arrays of
microtubule Microtubules are polymers of tubulin that form part of the cytoskeleton and provide structure and shape to eukaryotic cells. Microtubules can be as long as 50 micrometres, as wide as 23 to 27 nanometer, nm and have an inner diameter bet ...
s enveloped by cytoplasm. Axopodia are mostly responsible for phagocytosis by rapidly retracting in response to physical contact. These pseudopodia are primarily food-collecting structures, but also provide a means of hydrological transportation via the expansion of their surface areas. They are observed in "
Radiolaria The Radiolaria, also called Radiozoa, are unicellular eukaryotes of diameter 0.1–0.2 mm that produce intricate mineral skeletons, typically with a central capsule dividing the cell into the inner and outer portions of endoplasm and ect ...
" and "
Heliozoa Heliozoa, commonly known as sun-animalcules, are microbial eukaryotes (protists) with stiff arms (Pseudopodia#Morphology, axopodia) radiating from their spherical bodies, which are responsible for their common name. The axopodia are microtubule- ...
".


References

{{Authority control Actin-based structures Cell anatomy Cell movement