John Bovill Stem Cell

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Stem Cell Overview

What Are Stem Cells and Where Do They Come From?

Video Explanation

  • Stem cells are a population of cells within the body that are capable of differentiating into other cell types. Differentiation is the process of transitioning from one cell type to another. By differentiating, the cell specializes in what functions it is capable of performing, but also limits what it is capable of differentiating into in the future. Each transition between cell types is irreversible. Stem cells exist in two forms within the body, embryonic and adult stem cells. (1)
  • Embryonic stem cells are the cells that are generated early in the development of an embryo. They are totipotent developing into every cell type that eventually exists in the adult body of the organism. While an embryonic stem cell can differentiate into any type of cell, intermediate cell types or terminally differentiated cells (differentiated to the point where it will not transition cell types any further), cannot dedifferentiate back into an embryonic stem cell. Stem cells of this type can only be found within embryos, mostly very early in development. The number of cleavage divisions an embryo undergoes before losing totipotency varies between different species. (1) (2)
  • Adult stem cells exist within the fully developed adult body, where embryonic stem cells cannot be found. They have varying levels of potency, but are not totipotent. Many are pluripotent, meaning that they are capable of differentiation into several cell types. One type of adult stem cell is hematopoietic stem cells. These are still present in adult organisms and differentiate into every blood cell type that is observed in the body. (1)
    • Adult stem cell populations are created during development as embryonic stem cells differentiate into various cell types. Once embryonic stem cells have developed into adult stem cells, their population is self-replenished. This is accomplished by divisions of adult stem cells into two identical cells. When differentiating further, one of the two offspring cells will remain an adult stem cell, while the other daughter cell will differentiate further, maintaining the number of stem cells in the body. (1)
  • While naturally, stem cells are only capable of differentiating in a single direction, it is possible to induce adult body cells to pluripotency, effectively dedifferentiating them. This leads to the creation of stem cell populations that function identically to naturally existing pluripotent stem cells, and are then capable of differentiation into a variety of cell types, based on how much they were dedifferentiated. These are referred to as induced pluripotent stem cells.
    • These cells are genetically reprogramed to dedifferentiate by being forced to express genes and factors that are essential to the properties of embryonic stem cells. These cells demonstrate characteristics of pluripotency by expressing stem cell markers. In humans, induced pluripotent stem cells are even capable of generating cells of each of the three germ layers. (3)

Stem Cells in Development and Tissue Regeneration

  • The primary function of embryonic stem cells are to be totipotent and be responsible for being progenitors to every cell in the body during development.
    • These embryonic stem cells or inner cells that are found in the 3- to 5-day-old embryo (blastocyst) and give rise to the entire body of the organism:
      • Ex: All of the many specialized cell types and organs such as the heart, lungs, skin, sperm, eggs and other tissues. (1)
  • The function of adult stem cells are to be pluripotent and have the capacity to maintain or repair the tissue that they are found in due to normal wear and tear, injury, or disease (bone marrow, muscle, brain, etc). To divide for a long period of time and when called upon give rise to mature cell types that have specific functions, structures, or shapes for distinctive tissues. (1)
    • Ex: Hematopoietic cells
      • Non-terminally differentiated stem cells that contribute to the blood cell population while also self-replenishing.
      • Give rise to red blood cells, T and B lymphocytes, natural killer cells, neutrophils, basophils, eosinophils, monocytes, and macrophages.
    • Ex: Non-Hematopoietic cells
      • Small portion of stromal cell population in bone marrow that have the ability to generate cartilage, bone, and fat cells that aid in the formation of blood and fibrous connective tissue.
    • Ex. Neural Stem Cells
      • Found in the brain that give rise to nerve cell, astrocytes, and oligodendrocytes.
    • Ex. Skin stem cells
      • Most notably referenced to show the regenerative properties of stem cells
      • Found in the basal layer of epidermis. These cells lead to keratinocyte formation, which eventually find their way to surface of the skin. Once at the surface, the keratinocytes can form a protective layer (epidermis).
      • This process is easily seen when a minor cut or lesion occurs on the epidermis.

Stem Cells in Medicine

  • Further study of stem cells has provided an exciting era in science and medicine because of their potential to differentiate into any of the 200 cells of the body or regenerate and repair damaged tissues.
  • As mentioned, adult stem cells have unique regenerative abilities and such stem cells offer new potentials for treating diseases heart disease, organ failure, or cancer. However, there remains a lot of research to be done to obtain a full understanding of the use of stem cells in a medicinal aspect.
    • Ex: Induced pluripotent cells (3)
      • Genetically reprogrammed adult cells that resemble an embryonic stem cell-like state. This is done by being forced to express genes and essential factors for embryonic stem cell properties. It has been shown that human induced pluripotent stem cells have the potential to generate cells that are characteristic of each of the three germ layers.
      • If the introduced reprogramming factors by viruses is successful, these induced cells can act as useful tools for the modeling of diseases, transplantation medicine, and drug testing.
  • Stem cells allow researchers to gain more knowledge about the principal properties of cells and how they differ from further specialized cells. As research continues, the importance of stem cells grows as they are not just applied for regenerative medicine but can be used in in vitro to screen new drugs and to hopefully create model systems to learn more about the causes of birth defects and how they differ from the path of normal development. (2)
  • Research on stem cells continues to advance knowledge about how an organism develops from a single cell and how healthy cells replace damaged cells in adult organisms.
  • Overall, stem cells have many different exciting potential uses in medicine, but with these uses, arise obstacles that have yet to be overcome to make stem cell therapies and their applications completely effective. (1)

More Information

Potential Uses

Obstacles

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