The lamellipodium (pl. Lamellipodia) is a cytoskeletal actin projection on the mobile edge of the cell. cytoskeleton (also CSK is a cellular " Scaffolding " or " Skeleton " contained within the Cytoplasm. Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of The cell is the structural and functional unit of all known living Organisms It is the smallest unit of an organism that is classified as living and is often called It contains a two-dimensional actin mesh; the whole structure pulls the cell across a substrate (Alberts, et al, 2002). Within the lamellipodia are ribs of actin called microspikes, which, when they spread beyond the lamellipodium frontier, are called filopodia (Small, et all, 2002). The filopodia (also microspikes are slender cytoplasmic projections similar to Lamellipodia, which extend from the leading edge of migrating cells The lamellipodium is born of actin nucleation in the plasma membrane of the cell (Alberts, et al, 2002) and is the primary area of actin incorporation or microfilament formation of the cell. Nucleation is the onset of a Phase transition in a small region The cell membrane (also called the plasma membrane, plasmalemma, or "phospholipid bilayer" is a Selectively permeable Lipid bilayer Microfilaments (or actin filaments) are the thinnest filaments of the Cytoskeleton found in the cytoplasm of all Eukaryotic cells.
Lamellipodia are found primarily in very mobile cells, in particular the keratinocytes of fish and frogs, which are involved in the quick repair of wounds, crawling at a speeds of 10-20μm/minute over epithelial surfaces. The keratinocyte is the major cell type of the epidermis, making up about 90% of epidermal cells Fish are aquatic Vertebrate animals that are typically ectothermic (previously Cold-blooded) covered with scales, and equipped with two This article is about the block cipher algorithm For the ultrafast laser pulse measurement technique see Frequency-resolved optical gating. Wound healing, or wound repair, is the body's natural process of regenerating dermal and epidermal tissue. In biology and medicine epithelium is a tissue composed of cells that line the cavities and surfaces of structures throughout the body A lamellipodium separated from the main part of a cell by scratching across the cell with a pipette tip can continue to crawl freely about on its own. A pipette (also called a pipet pipettor or chemical dropper is a laboratory instrument used to transport a measured volume of liquid
Lamellipodia are a characteristic feature at the front, leading edge, of motile cells. They are believed to be the actual motor which pulls the cell forward during the process of cell migration. Cell migration is a central process in the development and maintenance of Multicellular organisms Tissue formation during embryonic development, Wound healing The tip of the lamellipodium is the site where exocytosis occurs in migrating mammalian cells as part of their clathrin-mediated endocytic cycle. Exocytosis (ek-soh-sy-TOH-sis Greek: Έξω - external and κύτος - cell is the durable process by which a cell directs secretory vesicles out of the Cell Clathrin is a Protein that is the major constituent of the 'coat' of the clathrin- Coated pits and coated Vesicles formed during Endocytosis Most animal cells take up portions of their surface Plasma membranes in a process called Endocytosis. This, together with actin-polymerisation there, helps extend the lamella forward and thus advance the cell's front. It thus acts as a steering device for cells in the process of chemotaxis. Chemotaxis, a kind of Taxis, is the phenomenon in which bodily cells bacteria, and other single-cell or Multicellular organisms direct their movements It is also the site from which particles or aggregates attached to the cell surface migrate in a process known as cap formation. When Molecules on the surface of a cell are Crosslinked they are moved to one end of the cell to form a “cap”
Structurally, the plus ends of the microfilaments (localized actin monomers in an ATP-bound form) face the "seeking" edge of the cell, while the minus ends (localized actin monomers in an ADP-bound form) face the lamella behind (Cramer, 1997). A monomer (from Greek mono "one" and meros "part" is a small Molecule that may become chemically bonded to other Adenosine-5'-triphosphate ( ATP) is a multifunctional Nucleotide that is most important as a " molecular currency" of intracellular Energy Adenosine diphosphate, abbreviated ADP, is a Nucleotide. It is an Ester of Pyrophosphoric acid with the Nucleoside Adenosine This creates treadmilling throughout the lamellipodium, which aids in the retrograde flow of particles throughout (ibid. Treadmilling is a phenomenon observed in many cellular cytoskeletal filaments, especially in Actin filaments and Microtubules. ). Arp2/3 complexes are present at microfilament-microfilament junctions in lamellipodia, and help create the actin meshwork. Arp2/3 complex is a seven-subunit Protein that plays a major role in the regulation of the Actin Cytoskeleton. Arp 2/3 can only join onto previously existing microfilaments, but once bound it creates a site for the extension of new microfilaments, which creates branching (Weed, et al, 2000). Another molecule that is often found in polymerizing actin with Arp2/3 is cortactin, which appears to link tyrosine kinase signalling to cytoskeletal reorganization in the lamellipodium and its associated structures (ibid. Cortactin (from “ cortical actin binding protein” is a monomeric protein located in the Cytoplasm of cells that can be activated by external stimuli to promote A tyrosine kinase is an Enzyme that can transfer a Phosphate group from ATP to a Tyrosine residue in a Protein. ).
Rac and Cdc42 are two Rho-family GTPases which are normally cytosolic but can also be found in the cell membrane under certain conditions (Small, et al, 2002). CDC42 is a protein involved in regulation of the Cell cycle. GTPases (singular GTPase are a large family of Hydrolase Enzymes that can bind and hydrolyze guanosine triphosphate (GTP. The cytosol or intracellular fluid (or cytoplasmic matrix) is the liquid found inside cells. When Cdc42 is activated, it can interact with Wiskott-Aldrich syndrome protein (WASp) family receptors, in particular N-WASp, which then activates Arp2/3. Wiskott-Aldrich syndrome (WAS is a rare X-linked recessive disease characterized by Eczema, Thrombocytopenia (low Platelet count The Wiskott-Aldrich Syndrome Protein ( WASp) is a 502- Amino acid protein that is expressed in cells of the Hematopoietic system This stimulates actin branching and increases cell motility (Small, et al, 2002). Motility is a biological term which refers to the ability to move spontaneously and actively consuming energy in the process Rac1 induces cortactin to localize to the cell membrane, where it simultaneously binds F-actin and Arp2/3. The result is a structural reorganization of the lamellipodium and ensuing cell motility (Weed, et al, 2000).
References
- Alberts, Bruce, et al. Molecular Biology of the Cell. Fourth Edition. Garland Science, Taylor & Francis Group. New York, 2002: pgs 908, 931, 973-975.
- Cramer, Louise P. Molecular Mechanism of Actin-Dependent Pretrograde Flow in Lamellipodia of Motile Cells. Frontiers in Bioscience, 2, d260-270, June 1, 1997.
- Small, Victor J. , et al. The lamellipodium: where motility begins. Trends in Cell Biology, Vol. 12 No. 3, March 2002: pgs. 112-120.
- Weed, Scott A. , et al. Cortactin Localization to Sites of Actin Assembly in Lamellipodia Requires Interactions with F-Actin and the Arp2/3 Complex. The Journal of Cell Biology, Vol. 151 No. 1, October 2, 2000. pgs 29-40. Available Online
- Lamellipodia at the Department of Cell Biology at IMB Salzburg
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