In the human body, more than 200 types of cells have been isolated, each of which has the same hereditary code. All of them developed first from a unicellular and then a multicellular embryo, which a little later divided into three germ layers. From each of its parts, body tissues have developed, where approximately the same type of cells are located. At the same time, almost all of them developed from the same group of predecessors. This process is called cell differentiation. This is a local adaptation of the cell to the real needs of the body, the implementation of the functions programmed in its hereditary code.
Characterization of cells and tissues
Somatic cells of the body have the same chromosome set, regardless of the functional purpose. However, they differ in phenotype, which is explained by their preparation to perform various local tasks inbiological tissues. A phenotype is the result of the expression of a specific genetic set in a specific environment. And under different conditions, cells with the same genetic material develop differently, have different morphological characteristics, and perform specific functions.
A highly developed organism needs this for the formation of many tissues that make up its organs. In this case, tissues are created from a homogeneous group of stem precursors. This process is called cell differentiation. This is a chain of events aimed at growing a cell population according to predetermined criteria for the growth and development of biological tissues of the body. It underlies the growth of an organism and its multicellular organization.
Essence of differentiation
In terms of molecular biology, cell differentiation is the process of activating some sections of chromosomes and deactivating others. That is, compact packing or unwinding of sections of chromosomes, which makes them available for reading hereditary information. In the conjugated state, when the genes are packaged in heterochromatin, reading is impossible, and in the expanded form, the desired sections of the genetic code become available for messenger RNA and subsequent expression. This means that cell differentiation is a non-strict regulated typing of the same type of chromatin packaging.
Cytokines and messengers
As a result, a group of cells differentiated into identicalconditions and having similar morphological features, there is a despriralization of identical sections of chromosomes. And in the course of exposure to intercellular messengers, local regulators of cell differentiation, the desired sections of genes are activated, and their expression occurs. And therefore, the cells of biological tissues produce the same substances and perform similar functions, for which this process is provided. From this point of view, cell differentiation is a directed effect of molecular factors (cytokines) on the expression of genetic information.
Membrane receptors
Cells of the same tissue have a similar set of membrane receptors, the presence of which is controlled by T-killers of the immune system. The loss of a cell receptor of the desired type or the expression of another, not intended for a given localization due to the risk of oncogenesis, causes directed cellular aggression against the “violator”. The result will be the destruction of the cell, the differentiation of which did not follow the rules provided for by the influence of intercellular messengers from specialized regulators.
Immune differentiation
Immune cells have special receptor molecules called differentiation clusters. These are the so-called markers, which can be used to understand the conditions under which immunocytes developed and for what purposes they are intended. They go through a long and complex process of differentiation, at each stage of which groups of lymphocytes that have developed an insufficient number of receptors are eliminated and destroyed, or in their interaction withantibodies detected "non-compliance".
Cell groups and tissues
Most body cells divide in two during mitotic reproduction. At its preparatory stage, the genetic information is doubled, after which two daughter cells with a similar set of genes are formed. Not only active parts of chromosomes are subject to copying, but also conjugated ones. Therefore, in tissues, differentiated cells after division give rise to two new daughter cells that have genetic material similar to the complete somatic set of chromosomes. However, they are unable to differentiate into other cells, since they cannot migrate naturally to other habitat conditions, that is, to other differentiation messengers.
Growth of cell population
Immediately after the division of two daughter cells, they receive a special set of organelles that they inherited from the mother. These smallest functional elements are already prepared to perform the necessary tasks in a given biological tissue. Therefore, the daughter cell only needs to increase the volume of the cavities of the endoplasmic reticulum and increase in size.
Also, the goal of cell development is to obtain an adequate supply of nutrients and bound oxygen. To do this, in the case of oxygen or energy starvation, it releases angiogenesis factors into the intercellular space. New capillary vessels sprout along these anchors, which will feed the group.cells.
The process of increasing in size, obtaining an adequate supply of oxygen and energy substrates, and expanding intracellular organelles with an increased rate of protein production is called cell growth. It underlies the growth of a multicellular organism and is regulated by numerous proliferation factors. At some point, upon reaching the maximum size, by a signal from outside or by coincidence, the grown cell will again divide in half, further increasing the size of the biological tissue and the organism as a whole.
Mesodermal differentiation
As a clear demonstration of the differentiation of stem cells and their more developed "descendants", we should consider the transformation of the mesodermal germ layer of the human body. From the mesoderm - a group of stem cells with the same structure and developing in the presence of differentiation factors, originate such cell populations as nephrotome, somite, splanchnotome, splanchnotomal mesenchyme and paramesonephric canal.
From each such population, intermediate forms of differentiation will originate, which will later give rise to the cells of an adult organism. In particular, three cell groups develop from the somite: myotome, dermatome, and sclerotome. Myotome cells will give rise to muscle cells, sclerotome - cartilage and bone, and dermatome - connective tissue of the skin.
The nephrotome gives rise to the epithelium of the kidneys and vas deferens, and the uterine epithelium will differentiate from the paramesonephric can altubes and uterus. The phenotype of splanchnotome cells will be prepared by differentiation factors for their transformation into mesothelium (pleura, pericardium and peritoneum), myocardium, adrenal cortex. The mesenchyme of the splanchnotome is the starting material for the development of cell populations of blood, connective and smooth muscle tissue, blood vessels and microglial cells.
The growth of cells in these populations, their multiple division and differentiation is the basis for supporting the viability of a multicellular organism. This process is also called histogenesis - the development of tissues from cellular precursors as a result of their differentiation and transformation of the phenotype in accordance with the influence of extracellular factors that regulate their development.
Plant cell differentiation
The functions of a plant cell depend on their location, as well as the presence of growth modulators and suppressors. The embryo of a plant in the composition of seeds does not have vegetative and germinal areas, and therefore, after germination, it must develop them, which is necessary for reproduction and growth. And until the favorable time for its germination comes, it will remain dormant.
From the moment the signal for growth is received, the functions of plant cells will begin to be realized along with an increase in size. The cell populations laid down in the embryo will go through a phase of differentiation and transform into transport routes, vegetative parts, germinal structures.
