Biological essence of stem cells
There is a special reserve of immature structures in the human body that ensure tissue renewal. The main feature of such cells lies in their dual potential: they can maintain their own population through self-replication and are capable of differentiation.
Interestingly, the process of development and maturation of these structures has unique embryological features. Unlike the standard pathway of multicellular organism development, stem cell differentiation bypasses the classic gastrulation stage. This means they do not require the prior formation of germ layers to form mature tissue.
These amazing cells were first successfully isolated in 1998. Since then, science has divided them into two main categories depending on the stage of organism development:
- Embryonic stem cells. They are obtained at the earliest stages of ontogenesis — at the blastocyst stage or from the tissues of a five-week-old embryo.
- Adult stem cells. This group includes, for example, hematopoietic cells present in an already formed organism.
Sources and differentiation potential
To obtain the necessary biological material in modern medical practice, umbilical cord blood cells and stromal cells extracted from bone marrow are most frequently used.
High therapeutic interest in these structures is due to their colossal differentiation potential. Under artificial or natural conditions, the most diverse specialized elements of the human body can form from an immature precursor:
- Neurons (cells of the nervous system).
- Hepatocytes (liver cells).
- Cardiomyocytes (heart muscle cells).
- Various types of epithelial cells.
Despite such impressive capabilities, the use of this resource has strict biological limitations. First, the natural supply of such cells in an adult body is extremely small. Second, they are subject to the so-called Hayflick limit — a strict restriction on the number of possible divisions, which is only 50–100 cycles.
Explantation: life outside the organism
The term explantation comes from the Latin words ex (out) and plantare (to plant). It designates a laboratory method for cultivating isolated organs, tissues, or individual cells outside a living organism. This approach is a simple and cost-effective way for long-term large-scale cultivation of human cells.
The significance of the explantation method cannot be overstated, as it spans several fundamental and applied directions simultaneously:
- Medical perspective. The technology clearly demonstrates the fundamental possibility of overcoming immunological incompatibility barriers during tissue transplantation.
- Clinical diagnostics. Cultivating peripheral blood cells allows doctors to accurately count the number of chromosomes. This is critically important for the timely diagnosis of various chromosomal disorders.
- Study of mutagenesis. The method provides an opportunity to study in detail the mechanisms of mutation origin directly in somatic cells.
Application in science and cell therapy
In addition to diagnostics, explantation serves as a powerful tool for conducting large-scale scientific research. Through in vitro tissue cultivation, scientists can study subtle stages of mitosis in real time and analyze cell differentiation processes in embryogenesis (these processes are actively studied using mammals and birds as examples). The method helps solve complex issues in cytology, histology, embryology, normal physiology, genetics, and even oncology.
Accumulated fundamental knowledge is now actively transitioning into the realm of practical medicine, forming the field of cell therapy. Cultured cell cultures are successfully used to treat severe pathologies, including:
- Stroke;
- Myocardial infarction;
- Liver cirrhosis;
- Diabetes mellitus and many other diseases requiring the restoration of lost or damaged tissues.
Briefly: answers to topical questions
What specific surface markers are used to isolate hematopoietic stem cells?
Membrane markers are used to isolate hematopoietic stem cells, the main one being the CD34 antigen. The phenotype of true human hematopoietic stem cells is characterized by the following set of markers:
- CD34 — a key marker of stem cells and their immediate progeny;
- Lin — lineage markers (absent on stem cells);
- CD38 — a marker of committed progenitor cells (absent on stem cell candidates).
Expression of the CD34 marker is absent on mature hematopoietic cells.
Which types of stem cells are classified as pluripotent and multipotent?
The following types of stem cells are classified as pluripotent and multipotent:
- Embryonic stem cells are pluripotent, can be isolated from the inner cell mass of the blastocyst, and give rise to all types of embryonic cells during embryogenesis.
- Regional / resident adult stem cells can be polypotent / multipotent: they give rise to a wide range of specialized cell types. An example is hematopoietic stem cells.
A mature organism's blood stem cell is classified as multipotent; the term "pluripotent" is not applicable to it.
What methods of in vitro cell cultivation exist, aside from explantation?
In addition to explantation, the cell culture method is widely used in vitro, classified according to cultivation and derivation methods. By cultivation method, they are distinguished into:
- Monolayer — monolayer cultures;
- Suspension — including perfusion cultivation;
- Mixed — combined types.
| Type by derivation | Characteristic |
|---|---|
| Organotypic | Whole tissue pieces |
| Primary | Can withstand 5–10 passages |
| Semi-continuous | Diploid, 40–50 passages |
| Continuous (cell lines) | Stable long-term passages from tumor tissues |
To understand the term "explantation," recall Latin: ex is the prefix "out" (as in export or exterior), and plantare is "to plant" (plantation). That is, it is literally "planting" cells outside the body.
Class and exam questions
What does the "Hayflick limit" mean with respect to stem cells?
This is a genetically programmed restriction on the number of somatic cell divisions. For stem cells, this limit ranges from 50 to 100 divisions.
What is specific about the development of stem cells compared to normal embryogenesis?
Their differentiation into specialized tissues can occur bypassing the gastrulation stage and without the formation of germ layers.
Why do doctors cultivate blood cells using the explantation method?
This is necessary for clinical diagnosis: during cultivation, cell division can be stopped, chromosomes counted, and chromosomal disorders detected.
At what stages are embryonic stem cells obtained?
They are usually isolated at the blastocyst stage of development or from an embryo at the fifth week of development.
What else to study on this topic
- Mechanisms of differentiation without the gastrulation stage
- Specifics of cell isolation at the blastocyst stage
- Overcoming immunological incompatibility in cell therapy
- Application of bone marrow hematopoietic cells
- Features of mutagenesis study in somatic cells
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