The basic and very important type of reorganizations of a korteks are psevdopodialny reactions: ejection, attachment and reduction of psevdopodiya. Let's consider in more detail these reactions. At ejection of a psevdopodiya on a cage surface very quickly, within several minutes or even seconds, the cytoplasm outgrowth is formed. Such outgrowth can have a different form. Internal structure of all types of psevdopodiya simply: they often do not contain any structures, except kortikalny mikrofilament. Thus in lamellopodiya these mikrofilament form the dense flattened network, and in bubbles – less ordered layer under a membrane.
In an organism the majority of cages, except for the cages floating in blood or a lymph is attached to each other and to fibrilla of a noncellular matriks. Therefore in such cages as well as in culture cages, the isometric tension is created.
The cytoskeleton consists of three main types of the threads forming three systems: mikrofilament, microtubules and intermediate filament. Each type of threads consists of one – two main proteins: mikrofilament – from an aktin, a microtubule – from a tubulin, intermediate filament – from special proteins, various in different fabrics: keratins – in epiteliya, a desmina – in muscles, a vimentina – in fabrics of the internal environment (connecting fabric, a cartilage, a bone, etc.), proteins of neyrofilament – in neurons.
Other example of reduction of an aktin-miozinovy bunch –, the last stage of cellular division when such bunch is formed between two sets of chromosomes. Contracting, such reducible ring divides two daughter cells.
All cages creep, forming on a first line dynamic outgrowths – psevdopodiya of a different form. In psevdopodiya under a membrane of a cage aktinovy mikrofilament which contact a and other proteins will be polymerized. Psevdopodiya can be attached to a surface of a substrate and, being reduced, pull all cage forward. Such is the main mechanism of the movement. Obviously, the direction of the movement is defined by at what edge of a cage psevdopodiya will be formed, attached and reduced.
From time immemorial it is known that muscles create a mechanical tension. If the point of an attachment of a muscle is mobile, this tension conducts to reduction of a muscle – such tension call isotonic. If this point is not mobile because of resistance of material to which this muscle is attached, the tension does not lead to reduction of a muscle – such tension call isometric. An example of an isometric tension – a tension which is created in muscles of the hand pulling the handle of strongly locked door.
The surface of the end of the thrown-out psevdopodiya can be attached to a substrate on which the cage creeps. Thus the place of strong contact where certain squirrels of a membrane the external end of a molecule unite to the proteins attached to a substrate is formed; the internal end the same molecule connects, through a number of intermediate links, with aktinovy mikrofilament of a psevdopodiya.
When the cage in culture is spread, that is strongly connected by contacts to a culture bottom from all directions – a substrate, the bunches of aktinovy mikrofilament connected to focal contacts cannot be reduced, their tension becomes isometric. Such cage all the time is in the strained, stretched state.
Remarkable achievement of the last decades – opening and research of system of the structures responsible for mobile architecture of a cage, for its movements and a form. The cytoskeleton – system of the proteinaceous threads filling cytoplasm appeared this system in cages.
It is confirmed by recent experiences of Shtossel. He found out that cages of one of lines of cages in culture stick out only spherical bubbles, but not lamellopodiya on a surface. it appeared that in a genome of these cages there was no the gene coding protein which connects aktinovy mikrofilamena in a network. By special methods of genetic engineering researchers entered a missing gene into cages, and then cages began to do not bubbles, but the flattened lamelopodiya. Thus, emergence in an aktinovy korteks of one additional protein is directed changed architecture of psevdopodiya.
What defines places of formation of psevdopodiya? In order that to understand it, we will consider the movements of one of the cages most often used in experiments cells of connecting fabric – fibroblast. They are polarized, that is form psevdopodiya only on one or two poles. These cages can creep is directed towards one of aktinovy poles. Their side edges are inactive.