Introduction to the science of stem cells; a new hope to mankind
You can be anything you want to be when you grow up!
Say the stem cells as they are a special type of cells that have a remarkable potential to renew themselves and an ability to differentiate into specific cell types. With their capability to regenerate and repair tissues, studies are conducted on its sources of origin, modes of differentiation, biological and chemical features and possible applications in the hope of finding a solution to some unsolvable issues regarding human health and medicine.
Two major characteristics are considered essential for a cell to be categorized under stem cells. One is its ability to renew itself to an unlimited number of cells which are identical to the original cell and the other is the ability to give rise to a special type of cell with the capability of becoming a part of a healthy animal. Although they can replicate themselves into a large number of cells, it happens in a controlled manner which distinguishes them from cancer cells (Biehl and Russell, 2009). Three major types of stem cells have been identified which are adult stem cells: found in all infants, children and adults although they are referred to as “adult”, embryonic stem cells and induced pluripotent stem cells or IPS: the ordinary cells tweaked by scientists to act like embryonic stem cells. Adult stem cells are extremely important as they are responsible for regenerating the skin, blood and hair of humans and contributes to the asexual reproduction of species like planaria whereas embryonic cells can be obtained from embryos fertilized in vitro, about five days after fertilization when the embryos reach the blastocyst stage. They can remain undifferentiated when provided with appropriate conditions for any desired time period. In the year of 2012, Shinya Yamanaka, a Japanese scientist was able to engineer a method to convert adult skin cells to pluripotent stem cells which were given the name as induced pluripotent stem cells or IPS. It was done by the addition of four different transcription factors, Oct4, Sox2, Klf4 and c-Myc that remove the identity markers of skin cells and reset them to the pluripotent state. They literally push the development back in time and have the ability to generate any type of cell in the body, creating a powerful way to dedifferentiate cells whose developmental fates have already been determined.
Potency of a stem cell
Potency or the varying ability to differentiate into specialized cell types is a significant feature of stem cells. They are classified as totipotent, pluripotent, multipotent and unipotent based on their potential to generate newer cell varieties and the number of cell types a cell can differentiate into increases in proportion to its potency. Cells derived from fertilized eggs are capable of generating all the embryonic and extra embryonic cells and thus are termed totipotent. Pluripotent stem cells or PCSs also bear the ability to generate all cell types in an organism but they lack the potential to contribute to extra embryonic cells such as placenta, differing them from totipotency. On the other hand, multipotent stem cells are lineage specific with limited differentiation potential and develop cell types specific to one particular tissue and being further restricted, unipotent stem cells possess the potential to generate only one single cell type.
How do they differentiate?
A stem cell becomes a specialized cell type through the process of cell differentiation which happens naturally in the developing embryo. Being pluripotent, an embryonic stem cell has the potential to make all cell types of the body. As it differentiates, it loses its potency and becomes more specialized. Cell signaling cascades in different locations define the formation of the three germ layers; the endoderm, mesoderm and ectoderm. Once a stem cell is differentiated into a germ layer, it becomes multipotent where it can only make cell types unique to that particular layer. The outermost layer which is the ectoderm gives rise to the nervous system and the epidermal skin cells while the middle layer or the mesoderm gives rise to the connective tissue and muscle cells in the body. The innermost endoderm serves as the origin of the digestive system and other inner organs in the body such as the lungs, pancreas, etc. A cell experiences many genetic and physical changes as it differentiates and when it becomes more specialized, the number of cells it can become gets fewer as it gradually loses its potency. Finally, it becomes unipotent and remains with the ability to become only one cell type.
Significance and current advancements
Identification and current advances in stem cells have opened a wider window in science and medicine. According to recent reports, researchers are considering applications of stem cell therapy to ameliorate common diagnoses such as diabetes and cancer along with rare diseases associated with the brain, blood, skin, and the immune system in hopes of providing a lifetime cure. These experiments have taken a newer dimension with the discovery of IPSs in 2012, with their ability to produce patient specific pluripotent stem cells. Researchers are currently investigating the potential utility of these induced pluripotent stem cells in disease modeling, drug development, toxicity testing and transplantation medicine with the hope of providing patients with an immune matched supply made of his or her own tissues. Furthermore, this technique gives an insight to the early stages of development in humans and it is not associated with ethical issues as such for embryonic stem cells which in turn makes its applicability much efficient.
Therefore, having an idea on the basics in the science of stem cells can be considered important with its wide applicability in various aspects along with associated side effects and risks they may result in, as this is what future looks into.
References
Biehl, Jesse K., and Brenda Russell. 2009. Introduction to Stem Cell Therapy. National Library of Medicine. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4104807/.
Stem Cell Research. n.d. Novus Biologicals. https://www.novusbio.com/research-areas/stem-cells.
