Cell migration is a central process in the development and maintenance of multicellular organisms. Tissue formation during embryonic development, wound healing and immune responses all require the orchestrated movement of cells in a particular direction to a specific location. Errors during this process have serious consequences, including mental retardation, vascular disease, rheumatoid arthritis, tumor formation and metastasis. An understanding of the mechanism by which cells migrate may lead to the development of novel therapeutic strategies for controlling , for example, invasive tumour cells. Cells in animal tissues often migrate in response to, and towards, specific external signals, a process called chemotaxis. Multicellular organisms are those organisms consisting of more than one cell, and having differentiated cells that perform specialized functions. ... Embryogenesis is the process by which the embryo is formed and develops. ... Wound healing, or wound repair, is the bodys natural process of regenerating dermal and epidermal tissue. ... The immune system is composed of a complex constellation of cells, organs and tissues, arranged in an elaborate and dynamic communications network and equipped to optimize the response against invasion by pathogenic organisms. ... It has been suggested that this article or section be merged with Coronary heart disease. ... Rheumatoid arthritis (RA) is traditionally considered a chronic, inflammatory autoimmune disorder that causes the immune system to attack the joints. ... Tumor (American English) or tumour (British English) originally means swelling, and is sometimes still used with that meaning. ... Metastasis (Greek: change of the state) is the spread of cancer from its primary site to other places in the body. ... Chemotaxis is a kind of taxis, in which bodily cells, bacteria, and other single-cell or multicellular organisms direct their movements according to certain chemicals in their environment. ...

Mechanism of migration

Background

The migration of single mammalian cells is usually viewed in the microscope as the cells move randomly on a glass slide. As the actual movement is very slow — usually a few micrometers/minute — time-lapse films are taken so that a speeded up movie can be viewed (see the fine movie of MDBK cells moving over a glass slide). This shows that, although the shape of a moving cell varies considerably, its leading front has a characteristic behaviour. This region of the cell is highly active, sometimes spreading forwards quickly, sometimes retracting, sometimes ruffling or bubbling. It is generally accepted that the leading front is the main motor which pulls the cell forward. How does it perform its ruffling, spreading function? The simple answer is that we do not fully understand how it acts. However, because the locomotion of all mammalian cells (except sperm) has several common features, the underlying processes are believed to be similar. The two main constant features are: (1) the behaviour of the leading front. (2) the observation that any debris on the dorsal surface of the cell moves backwards on the cell’s surface towards its trailing end. The latter feature is most easily observed when aggregates of a surface molecule are cross-linked with a fluorescent antibody (see cap formation) or when small beads become artificially bound to the front of the cell. Besides mammalian cells, many other eukaryotic cells appear to move in a similar way. Thus, one of the most valuable model creatures for studying locomotion and chemotaxis is the amoeba Dictyostelium discoideum. A decaying peach over a period of six days. ... The contents of the Sperm article were merged into this article and now redirects here. ... Schematic of antibody binding to an antigen An antibody or immunoglobulin is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. ... There are very few or no other articles that link to this one. ... This article, image, template or category should belong in one or more categories. ...

Molecular processes at the front

The evidence for what is happening at the leading front comes from several different directions, the most important of which is that:

Two different models for how cells move. A) Cytoskeletal model. B) Membrane Flow Model

— it is a site of rapid actin polymerisation: soluble actin monomers polymerise to form filaments. This has led to the view that it is the formation of these actin filaments which pushes the leading front forward and is the main motile force for advancing the cell’s front. Image File history File links Cellmigrationmodels. ... G-Actin (PDB code: 1j6z). ...

— it is the site at which membrane is returned to the cell surface from internal membrane pools at the end of the endocytic cycle. This has led to the view that extension of the leading edge occurs primarily by addition of membrane at the front of the cell. If so, the actin filaments which form at the front might stabilise the added membrane so that a structured extension, or lamella, is formed rather than the cell blowing bubbles at its front. For a cell to move, it is necessary to bring a fresh supply of feet — those molecules, called integrins, which attach a cell to the surface on which it is crawling — to the front. It is likely that these feet are brought to the front by the membrane added there. Most animal cells take up portions of their surface plasma membranes in a process called endocytosis. ... An integrin, or integrin receptor, is an integral membrane protein in the plasma membrane of cells. ...

The nucleus and rear

Given that a cell’s front advances, what about the rest of the cell? Is it simply dragged forward, like a sack? We do not know, but there are suggestions that the nucleus and perhaps other large structures inside the cell may also be pulled forward by actin filaments. In addition, it may be that the rear of the cell actively contracts, as it is here that, in some cells, the major contractile protein myosin is found. In cell biology, the nucleus (from Latin nucleus or nuculeus, kernel) is found in all eukaryotic cells and contains the nuclear genes which form most of the cells genetic material. ... Myosin is a motor protein filament found in muscle tissue. ...

Mutants

Insight into how complex biological processes work can often be gleaned from a study of mutations. In the case of the intracellular mechanisms underlying cell movement, this has been largely unsuccessful. Thus, although many mutants are known in Drosophila which affect migratory processes, these tend to fall into two groups: transcription factors (such as slow border cells which affects oocyte development) or key regulator proteins (such as JNK which controls dorsal closure). These tell us little about how cells actually move. Another major source of mutants is the haploid amoeba Dictyostelium. Many single copy genes associated with cytoskeletal function have been deleted: these mutants usually have only a weak phenotype, suggesting either that these genes are not required for locomotion or that there are multiple mechanisms by which cells can move. However, temperature-sensitive mutants in the NSF gene rapidly block cell migration indicating that the NSF protein, which is required for intracellular membrane transport, is somehow needed for cell movement. Type Species Musca funebris Fabricius, 1787 Drosophila is a genus of small flies whose members are often called small fruit flies, or more appropriately vinegar flies, wine flies, pomace flies, grape flies, and picked fruit-flies. ... Haploid (meaning simple in Greek) cells have only one copy of each chromosome. ... The phenotype of an individual organism is either its total physical appearance and constitution or a specific manifestation of a trait, such as size, eye color, or behavior that varies between individuals. ... N-ethylmaleimide sensitive fusion protein (originally termed N-ethylmaleimide sensitive factor, hence the acronym NSF) is the name of a protein that is critically involved in the release of neurotransmitter at the neuronal synapse. ...

Cell polarity

Migrating cells clearly have a polarity: a front and a back. How this arrow is formulated at a molecular level inside a cell is unknown. In a cell which is meandering in a random way, the front can easily give way to become passive as some other region of the cell forms a new front. In chemotaxing cells, the stability of the front is enhanced and the cell seems purposively to advance towards its target. This polarity is reflected at a molecular level by a restriction of certain molecules to particular regions of the cell surface: thus the phospholipid PIP3 and activated Rac and CDC42 are found at the front of the cell, whereas Rho and PTEN are found towards the rear. It is believed that microtubules and filamentous actin are important for establishing and maintaining a cell’s polarity. Thus, drugs which destroy microtubules disrupt the polarity of many cells; drugs which destroy actin filaments have multiple and complex effects. It may be that, as part of the locomotory process, membrane vesicles are transported along these filaments to the cell’s front. In chemotaxing cells, the increased persistence of migration towards the target may result from an increased stability of the arrangement of the filamentous structures inside the cell and which determine its polarity. In turn, these filamentous structures may be arranged inside the cell according to how molecules like PIP3 and PTEN are arranged on the inner cell surface. And where these are located appears in turn to be determined by the chemoattractant signals as these impinge on specific receptors on the cell’s outer surface. Chemical structure of sn-1-stearoyl-2-arachidonoyl phosphatidylinositol 3,4,5-trisphosphate Phosphatidylinositol (3,4,5)-trisphosphate (PtdIns(3,4,5)P3) commonly abbreviated to PIP3 is the product of the class I phosphoinositide 3-kinases (PI 3-kinases) activity on Phosphatidylinositol (4,5)-bisphosphate. ... PTEN with ligand tartaric acid. ... Microtubules are protein structures found within cells, one of the components of the cytoskeleton. ... In cell biology, a vesicle is a relatively small and enclosed compartment, separated from the cytosol by at least one lipid bilayer. ... Drawing of a cell membrane A cell membrane, plasma membrane or plasmalemma is a selectively permeable lipid bilayer coated by proteins which comprises the outer layer of a cell. ... In biochemistry, a receptor is a protein on the cell membrane or within the cytoplasm or cell nucleus that binds to a specific molecule (a ligand), such as a neurotransmitter, hormone, or other substance, and initiates the cellular response to the ligand. ...

References

• A cell's sense of direction
• Membrane Flow and the Cytoskeleton Cooperate in Moving Cells
• Cell Migration: Integrating signals from front to back
• Regulation of microtubules in cell migration
• Cell Migration Gateway The Cell Migration Gateway is a comprehensive and regularly updated resource on cell migration
• Cell Migration 101 A Primer on Cell Migration
• Cell Migration Knowledgebase: A comprehensive cell migration database of proteins, families, complexes and othologs

See also

• Endocytic cycle