The Description of the Individual Components of the Embryonic Biological Preparations
 
What are these cells famous for? Why has the attention of the international scientific community been drawn to their research for the last twenty years?

The main property of an embryonic stem cells is that the genetic information about development and functioning of a living organism which is held in the nucleus is in the "zero" starting point. All the non-sexual (somatic) cells of the living organisms are specialized, they carry out certain functions: marrow cells form the skeleton, blood cells are responsible for the immunity, and oxygen transportation, nerve cells transfer electric impulses, etc. An embryonic stem cell has not yet turned on the mechanisms that define its specialization. At the zero starting point its genome has not yet started a single program, and what is most important - has not yet started a duplication program. There are very few cells of this kind in an organism, a 100th shares of a percent, that is why it is so difficult to get and research this population in its pure state.

The fact is that stem cells can accept any program and turn into any one of the possible types of embryonic cells; they are waiting for the signal to begin one of their transformations. Embryonic stem cells in contrast to all somatic cells do not have any functions except for the transfer of the mRNA into the next cells generation, it is a cartridge with information, the anonymous cell and as professor V. Repin has called it, the cell "without a name and patronymic".

The information contained within the genetic material of a fertilized egg has not yet realized its means of DNA and RNA activity of acids, the mechanism of the biochemical and structural components formation which determines the specific features of the developing cells have not been initiated yet. After the discovery of the double-stranded model of DNA by Watson and Crick in 1953 it became clear where the hereditary information is kept and how it is transferred. In 2001 scientists had completely decoded the human DNA structure, but they have yet to understand how the genes composing it actually work. Embryonic stem cells were the only ones that turned out to be the great model for understanding how 5,000 genes of embryogenesis duplicate genetic information so that a human organism, consisting of 10¹⁴ cells, would grow out of a single cell.

A genome's total activity is controlled by a certain set of genes which at first form the cell's skeleton, then its internal structure (organelles), and after that the whole cell. If compared to a computer, a genome can be called the software. At the very last moment of this genetic program it is determined what the specialization and place in an organism is started, deciding if the cell will become somatic tissue or turn into a blood cell.

During the interphase stage (between two mitotic cell divisions) DNA present in the nucleus has molecule parts free from proteins which could block its activity. In these parts the transcription of a matrix of information RNA (mRNA) which through the nuclear interstices enter the cytoplasm occurs . Depending on the molecular structure and the cell's type, mRNA activity can take one of two possible routes:

Synthesis of endo-cellular proteins (structural proteins and enzymes) that occur by means of connecting mRNA with ribosomes,

Synthesis of extra-cellular proteins (immunoglobulins, collagen) at which mRNA interacts with the granular endoplasmic reticulum. Newly formed polypeptide chains enter the Golgi complex, connect with the polysaccharide molecules, after that they move into the cell membrane and enter the intercellular space.

All the stages of protein synthesis are initiated under the influence of the regulatory mechanisms which are located intra- as well as extracellularly. Extracellular influences are usually carried out by means of receptor molecules located at the cells' surface. Many proteins located in the external layer of the membrane create complexes with polysaccharides and are the hormones' and growth factors' receptors.

For instance, during the cultivation of embryonic stem cells in order to get a homogenous population of specialized mammal and human clones, three growth factors are used. Three cytokines, which in the presence of a substratum of mouse fibroblast layered on a cultural dish, stimulate constant division of undifferentiated and unattached to substratum spheroid cells. All the cells of our organism have the same set of genes that work on "different genetic programs". Only single cells can turn into an organism consisting of billions of cells. For this purpose embryogenesis genes exist to regulate this process at the initial stage of the embryo's development.

After fertilization by a spermatozoon the zygote is formed, which is a cell with a full set of chromosomes in which genes are in a repressed state. As the development continues, the depression of certain gene groups occurs and off genes responsible for the proliferation and general metabolism of cells.

Within 30 hours of fertilization, the zygote starts to divide and by the fourth day a 16-celled embryo-morula is formed. At the stage of morula formation embryonic cells are totipotent, that is, they have a potential to generate all the cells and tissues that make up an embryo. The zygote divides and differentiates until it produces a mature organism; rabbits and sheep keep this ability up to 8, and cows up to 32 cells. As the division and growth of cells takes place the embryo passes on to the blastocyst stage during which cells lose properties of totipotency and become pluripotent. Most scientists use the term pluripotent to describe stem cells that can give rise to cells derived from all three embryonic germ layers - mesoderm, endoderm, and ectoderm. External blastocyst cells turn into the amniotic formations, and internal start forming the organs' tissues. During this period part of the stem cells are collected with in the embryo's yolk sac and liver. Starting from the 12th week of human embryo development stem cells move to spleen, marrow, and other organs.

Up into the 12th week of development an embryo's cells are not immunologically relevant - that means they do not cause the rejection reaction during the transplantation which plays an important role in cell therapy. At the gastrula stage the divided cells create germ layers with stem cells giving rise to specialized tissues. During this period genes regulating more specified functions of the differentiated cells are activated. Thus, at each stage of embryonic development certain gene activation, which comprises 5-10% of their total number occurs, at the other - they are repressed and other genes become active. We see that as an embryos development goes on, the potency of the dividing cells is gradually decreased, the chances to select the direction of the cells development is also decreased. This phenomenon in embryology is called restriction.

Research of ways embryonic stem cells transform is especially important for medicine because knowing them, it is possible to cultivate any kind of tissue, any human organ in a test tube. Embryonic stem cells alone are not sufficient for the completion of such tasks, specialized stem cells already have their differentiation direction and can under growth factors turn into blood cells, muscular tissue, vessels, etc.