Under cell migration (latin migrare, hiking ' ) is the active locomotion ( locomotion ) of cells or cell clusters. The generic term " migrating " includes the non-directional spontaneous movement (random migration) directed chemotactic movement and the change of the moving speed ( Chemokinetik ). Within a metazoan organism only certain cells are capable of migration: embryonic cells, and in the mature organism, certain cell types of the connective tissue, blood vessels, some epithelial cells, tumor cells and in particularly high degree, the immune system cells and the sperm. In prokaryotic organisms migration takes place by means of flagella and cilia.
Locomotion by flagella and cilia
Sperm move by means of a whip ( flagellum ) and need for open liquid areas. Also many prokaryotes obtain the necessary flagella motility, however, the structure of the prokaryotic flagellum is completely different than in eukaryotes. Cilia are found exclusively in eukaryotic cells. The most prominent examples by means of cilia, motile cells are paramecium and ciliates ( ciliates ).
For somatic cells that migrate to the narrowness of the structures that are amoeboid movement is advantageous because it allows considerable deformation and adaptation to the existing spatial conditions. Many eukaryotic cells, such as fibroblasts, keratinocytes, neurons, immune cells and of course amoebae are capable of amoeboid movement to migrate.
The amoeboid movement is essentially based on the dynamic transformation of two cell structures and on the attachment to the extracellular matrix: On the extension of fibrillar proteins (actin ) and the installation of membrane vesicles in the direction of movement, resulting in the formation of cell protrusions ( filopodia and lamellipodia ) result. In lamellipodia and filopodia, a framework of high-molecular, fibrillar F- actin is built up, which continues to grow at the leading edge by growing low molecular weight G- actin, whereas it again decays to its rear in G -actin (so-called treadmilling, treadmill occurred). At the same time the leading edge of the lamellipodium is extended by the incorporation of membrane material derived from the cell's own vesicles. These vesicles are transported along a further fibrillar structure, the microtubule forward. In this way the Aktingerüst wanders into the sac of the Lamellopodiums that feeds itself by installing new membrane material further. Meanwhile, explore filopodia, also driven by growing actin filaments ahead, at the front of Leitsaums ( leading edge ) the environment for suitable conditions for Nailing substrate. Focal complexes of filopodia ( filopodial focal focal complexes ) then make the first contact with the extracellular matrix ( ECM), thereby forming with further advancement of the cell, stable focal adhesions in the lamellipodium.
With the vesicles membrane-bound receptors for chemotaxins and growth factors, adhesion to proteins with which the cell at its base attached ( adhesins ) and other types of receptors at the front of the migrating cell to be installed and constantly updated. The Aktingerüst, which is held together by various cross-linking proteins, connects to these receptors and lamellipodia and filopodia stability and provides the necessary propulsion for the hike. Depending on the cell type, enter the vesicles, when installed, enzymes and oxygen radicals to the outside, which will loosen up the tissue and thus facilitate cell movement ( " enzymatic machete "). The membrane material, which permanently occurs at the front of the Lamellopodiums for installation, moves gradually to the rear side of the cell where it is drawn along with the receptors in the form of vesicles, which regenerates the Golgi apparatus and will be transported back to the front, in order to further progress to enable lamellipodia and filopodia ( membrane flux ). At the same time Aktingerüst contracts by means of the motor protein myosin, resulting in a pressure within the cell builds up which ( in contrast to the gel-like state at the rear end of the unit cell) can escape to the front due to the sol- aggregate state in the direction of movement only. In this way the rear part of the cell is pulled, while the front part continue to expand. A wandering amoeboid cell thus moves through relocation and contraction of their support and holding stand in the desired direction. Play a pivotal role in the filopodia that determine by the " scanning " the environment, the education, orientation and localization of focal adhesions and thus the direction of movement.
Tasks of cell migration
The tasks of cell migration are manifold: morphogenetic movements in the embryonic period and during growth; later structural transformation, regeneration, healing, etc. For the cells of the immune system it is significant to find harmful material. The most agile of immune cell is the neutrophil granulocyte which in a resting diameter of about 7.5 microns to stretch up to 70 microns and can migrate through gaps down to 0.6 microns. His walk rate is depending on the conditions 10 to 20 microns per minute. The ability to promote migration of the metastasis of tumor cells.