Tag Archives: embryonic

Biology of stem cells: an overview – PMC – National Center for …

Posted: March 19, 2024 at 2:38 am

Kidney Int Suppl (2011). 2011 Sep; 1(3): 6367.

1Department of Genetics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

1Department of Genetics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

2Postgraduation Program in Genetic and Molecular Diagnosis, Universidade Luterana do Brasil, Canoas, Brazil

1Department of Genetics, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil

2Postgraduation Program in Genetic and Molecular Diagnosis, Universidade Luterana do Brasil, Canoas, Brazil

Stem cells are defined as precursor cells that have the capacity to self-renew and to generate multiple mature cell types. Only after collecting and culturing tissues is it possible to classify cells according to this operational concept. This difficulty in identifying stem cells in situ, without any manipulation, limits the understanding of their true nature. This review aims at presenting, to health professionals interested in this area, an overview on the biology of embryonic and adult stem cells, and their therapeutic potential.

Keywords: adult stem cells, biological characteristics, cell therapy, embryonic stem cells, human diseases

Although the initial concept of stem cells is more than 100 years old,1 and much of its biology and therapeutic potential has been explored in the past three decades, we still know little about their true nature. This review is intended to provide an overview on the biology of stem cells and their therapeutic potential to those interested in this field.

Stem cells are operationally defined as cells that have the potential for unlimited or prolonged self-renewal, as well as the ability to give rise to at least one type of mature, differentiated cells.2, 3 Although this basic definition of stemness' applies generally to stem cells, it is necessary to individually consider embryonic and adult stem cells as they do not share much more than the name and the basic definition above.

In humans, the embryo is defined as the organism from the time of implantation in the uterus until the end of the second month of gestation. Embryonic stem cells (ESCs), however, refer to a much more restricted period, resulting from the isolation and cultivation of cells from the blastocyst, which forms at approximately 5 days after fertilization.4

The zygote, which is the cell resulting from the fertilization of an oocyte by a spermatozoon, is totipotent. Several successive cell divisions generate the morula, with 3264 totipotent cells. After that stage, it develops into the blastocyst, which consists of a hollow ball of cells. Peripheral cells (the trophoblast) of the blastocyst generate the embryonic membranes and placenta, whereas the inner cell mass develops into the fetus. These are the cells that are used to establish stem cell cultures (). They are not totipotent, as they do not have the ability to support the formation of another embryo, and are considered to be pluripotent as they can produce all the cell types of the adult organism. Further development of the embryo leads to the formation of the gastrula, composed of the three germ layers (ectoderm, mesoderm, and endoderm), from which the complete organism develops.

Embryonic stem cell cultivation. The zygote undergoes successive mitotic divisions until a sphere of cellsthe blastocystis formed. In the blastocyst, the trophoblast at its periphery generates the embryonic membranes and placenta, whereas the inner cell mass develops into the fetus. Embryonic stem cells are immortal in culture, having been established from one pluripotent cell collected from the inner cell mass. These are capable of differentiating into any of the mature cell types present in the adult organism.

In 1981, two groups established the first ESC lines from mouse blastocysts, and in 1998 the first human ESC line was generated.5 Although seemingly simple, the procedure is technically demanding because of the need for strictly controlled conditions necessary for the maintenance of the cells in the undifferentiated state. This is particularly important for human ESCs.6 Once established, ESC lines may be maintained in permanent culture, frozen and thawed, and transported between laboratories. It is estimated that there are currently around 250 human ESC lines in the world, widely shared among different groups. The process of establishing an ESC line requires, however, the destruction of the blastocyst, raising ethical issues as scientific investigation alone is not capable of determining whether blastocysts constitute human beings. An alternative method involves the production of ESCs by collection of only one cell from the inner cell mass, allowing implantation of the remaining cells in the womb. However, ethical considerations still remain as it has to be tested whether the remaining cells can develop into a normal human being.

Cultured ESCs show defined characteristics: they are pluripotent, capable of differentiating into cells derived from all three germ layers; they are immortal in culture and may be maintained for several hundred passages in the undifferentiated state; and they maintain a normal chromosomal composition.

Molecular characterization of ESCs is well developed, and they are known to express surface markers such as CD9, CD24, and alkaline phosphatase, and several genes involved with pluripotency, including Oct-4, Rex-1, SOX-2, Nanog, LIN28, Thy-1, and SSEA-3 and -4.7 Expression of high levels of telomerase explains their immortality in culture.

ESC research focuses mainly on two issues, both of which have shown significant progress in the past few years.6 The first point explores how to better maintain the cells in long-term culture, without significant modifications of their genetic composition and, in the case of human ESCs, avoiding the need for animal products in the culture. Generally, the cells are maintained in culture on feeder cells such as mouse fibroblasts. The second point focuses on how to differentiate the cells into the many mature cell types that are necessary for the potential treatment of different diseases. ESCs can be induced to differentiate into various cell types in suspension culture, resulting in three-dimensional cell aggregates called embryoid bodies. This tendency of ESCs to differentiate spontaneously may not always be desirable. A technical challenge is to control the differentiation process: although the addition of growth factors directs the differentiation process, usually the cultures spontaneously differentiate into various cell types. It is thus necessary to use methods that allow removal of undifferentiated ESCs from cultures in which the differentiated cell types are the desired product.

Recently, methods for direct reprogramming of adult cells to induced pluripotent stem cells have been developed.8 In the process, mature cells from the patient are treated in vitro with genes that dedifferentiate' them to a pluripotent stage, similar to an ESC (). Induced pluripotent stem cells are believed to be identical to natural pluripotent ESCs in many respects, including the expression of specific genes and proteins, chromatin methylation patterns, culture kinetics, in vitro differentiation patterns, and teratoma formation. Besides avoiding the ethical issues associated with the destruction of human embryos, this approach allows the generation of patient-specific cells of any lineage. Problems related to the genetic modification of target cells, however, must still be resolved before induced pluripotent stem cells may be clinically tested.

Production of induced pluripotent stem (iPS) cells. iPS cells are produced by treating mature cells, such as fibroblasts, with genes that dedifferentiate' them to a pluripotent stage, similar to an embryonic stem cell. Viral vectors, such as retroviruses, are generally used for gene transfer. The transformed cells become morphologically and biochemically similar to pluripotent stem cells, with the advantage of representing autologous cells in therapeutic applications.

The principal advantage of ESCs over adult stem cells is related to their pluripotency and limitless expansion in culture, as they have the potential to give rise to all cell types composing the adult organism. This potential is exploited in vitro to develop specialized cells that are then used in therapy.

Owing mainly to safety issues, the clinical use of hESCs is much more restricted than that of adult stem cells. As proof of pluripotency, ESC lineages injected into immunodeficient mice must lead to teratoma formation, with derivatives of all three germ layers. Only differentiated cells derived from ESCs may be administered to patients, as any contaminating undifferentiated cells could give rise to cancer. The first clinical trial using human ESC-derived cells, which in this case are oligodendrocyte progenitor cells, was started in October 2010. Care must be taken, however, to not call this procedure human ESC therapy', as the cells to be used are no longer ESCs.

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What are Stem Cells? – Types, Applications and Sources – BYJU’S

Posted: March 19, 2024 at 2:38 am

Stem cells are special human cells that can develop into many different types of cells, from muscle cells to brain cells.

Stem cells also have the ability to repair damaged cells. These cells have strong healing power. They can evolve into any type of cell.

Research on stem cells is going on, and it is believed that stem cell therapies can cure ailments like paralysis and Alzheimers as well. Let us have a detailed look at stem cells, their types and their functions.

Also Read: Gene Therapy

Stem cells are of the following different types:

The fertilized egg begins to divide immediately. All the cells in the young embryo are totipotent cells. These cells form a hollow structure within a few days. Cells in one region group together to form the inner cell mass. This contains pluripotent cells that make up the developing foetus.

The embryonic stem cells can be further classified as:

These stem cells are obtained from developed organs and tissues. They can repair and replace the damaged tissues in the region where they are located. For eg., hematopoietic stem cells are found in the bone marrow. These stem cells are used in bone marrow transplants to treat specific types of cancers.

These cells have been tested and arranged by converting tissue-specific cells into embryonic cells in the lab. These cells are accepted as an important tool to learn about the normal development, onset and progression of the disease and are also helpful in testing various drugs. These stem cells share the same characteristics as embryonic cells do. They also have the potential to give rise to all the different types of cells in the human body.

These cells are mainly formed from the connective tissues surrounding other tissues and organs, known as the stroma. These mesenchymal stem cells are accurately called stromal cells. The first mesenchymal stem cells were found in the bone marrow that is capable of developing bones, fat cells, and cartilage.

There are different mesenchymal stem cells that are used to treat various diseases as they have been developed from different tissues of the human body. The characteristics of mesenchymal stem cells depend on the organ from where they originate.

Following are the important applications of stem cells:

This is the most important application of stem cells. The stem cells can be used to grow a specific type of tissue or organ. This can be helpful in kidney and liver transplants. The doctors have already used the stem cells from beneath the epidermis to develop skin tissue that can repair severe burns or other injuries by tissue grafting.

A team of researchers have developed blood vessels in mice using human stem cells. Within two weeks of implantation, the blood vessels formed their network and were as efficient as the natural vessels.

Stem cells can also treat diseases such as Parkinsons disease and Alzheimers. These can help to replenish the damaged brain cells. Researchers have tried to differentiate embryonic stem cells into these types of cells and make it possible to treat diseases.

The adult hematopoietic stem cells are used to treat cancers, sickle cell anaemia, and other immunodeficiency diseases. These stem cells can be used to produce red blood cells and white blood cells in the body.

Stem Cells originate from different parts of the body. Adult stem cells can be found in specific tissues in the human body. Matured cells are specialized to conduct various functions. Generally, these cells can develop the kind of cells found in tissues where they reside.

Embryonic Stem Cells are derived from 5-day-old blastocysts that develop into embryos and are pluripotent in nature. These cells can develop any type of cell and tissue in the body. These cells have the potential to regenerate all the cells and tissues that have been lost because of any kind of injury or disease.

To know more about stem cells, their types, applications and sources, keep visiting BYJUS website.

Stem-cell therapy is the use of stem cells to cure or prevent a disease or condition. The damaged cells are repaired by the generated stem cells, which can also hasten the healing process in the injured tissue. These cells are essential for the regeneration and transplanting of tissue.

Stem cells have the capacity to self-renew and differentiate into specialized cell types. Totipotent stem cells come from an early embryo and can differentiate into all possible types of stem cells.

The four types of stem cells are the embryonic stem cells, adult stem cells, induced pluripotent stem cells and mesenchymal stem cells

Adult stem cells are undifferentiated cells taken from tissues and developing organs. They can replace and restore damaged tissues. Example hematopoietic stem cells in the bone marrow.

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