The remarkable restorative properties of stem cells have revolutionized regenerative medicine. All cells in the bodies of humans originated from a precursor cell that had the potential to divide and migrate into different forms with specialized functions. These replicative cells are often collected from a group of embryonic stem cells called the inner cell mass (ICM). Modern medicine allows researchers to take the ICM, while it’s being formed during the early stages of development, and grow it in a lab, indefinitely. By adding several growth factors, the cultured cells can be shaped into any configuration necessary for experimentation.
What Is A Stem Cell Line?
For research purposes, a stem cell line is a group of stem cells cultured in vitro for continuous propagation. The stem cell lines are derived from either animal or human tissue and can be collected from different sources: blastocyst, juveniles, adults, or induced to become stem cells. Stem cells possess several properties, but the two most important for investigation are self-renewal and pluripotency/multipotency. Self-renewal allows the cells to divide indefinitely while remaining in their unique undifferentiated state. Pluripotency or multipotency allows the cells, under physiological or experimental conditions, to differentiate into specialized tissue or organ cell types. In some organs, stem cells can regularly divide to repair or replace damaged tissue.
Although this sounds like immortalized cell lines, tumorous cells that cannot stop dividing or cells that have been artificially manipulated to proliferate indefinitely, there’s a very subtle difference. Immortalized cell lines are created because their mutations removed their ability to halt their cellular division. On the other side, stem cells are genetically purposed to multiply and specialize. As a result, they naturally retain their original genetic qualities after division. Therefore, the resplendence behind stem cell lines in regenerative medicine is their ability to retain the individual’s uniqueness while aggregating and migrating. At present, about 15 human embryonic stem-cell lines are publicly available, although they vary in their usefulness toward research.
Types of Stem Cell Lines
As we know, because of stem cell’s extensive ability to form other cell types, stem cell lines are extremely useful in development, disease, and treatment. In total, there are three types of stem cell lines – those cultured from the blastocyst, adults or generated as a result of induced stem cell research.
Embryonic stem cells – collected from blastocysts are the easiest to culture due to their abundance. All human embryonic stem cell lines in use today were created from embryos generated by vitro fertilization (IVF) and donated by the couple for research purposes. Some of these eggs will be fertilized, and after fertilization, the cells divide to form the ball of cells called the blastocyst. Alterations of genetic diagnosis can allow the generation of embryonic stem cells from single cells removed from embryos in a process similar to genetic testing. Those stem cells can also be derived from eggs that have been activated in a way in which the eggs are induced to divide without fertilization.
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Adult stem cells were once thought to exist in smaller quantities throughout the differentiated cells in a tissue or organ. However, recently, scientists have found adult stem cells in many more tissues than previously thought – like the heart and brain – which has led to more discoveries in stem cell therapy. The primary job for adult stem cells is usually to maintain and repair the tissue in which they’re found. In living animals, adult stem cells are available to divide for a long period of time and can give rise to mature cell types with the characteristic shapes and functions related to their particular tissue. However, with transdifferentiation experiments – factors introduced to the cell that causes it to differentiate into cell types unrelated to its lineage – researchers are able to create brain stem cells that could differentiate into blood cells or blood-forming stem cells that differentiate into cardiac muscle.
Induced stem cells are adult cells that have been genetically reprogrammed and require a complex series of growth factors in order to create them. The benefit is the creation of an embryonic stem cell-like form that has similar properties to embryonic stem cells. Despite this recent development in stem cells, induced stem cells are already incredible tools for drug development and modeling of diseases. However, the virus necessary to introduce the stem cell factors – creating pluripotency – has sometimes caused cancers and this approach had scientists questioning whether non-viral delivery strategies will be as effective.
The Future of Stem Cells
However, the two current pluripotent types of stem cell lines, embryonic stem cells and induced pluripotent stem cells, have certain limitations. Despite being pluripotent, researchers are unable to produce every single type of cell since some of them are excluded from becoming certain cell types. For example, some human embryonic stem cells can have altered growth phases of the cell cycle – preventing certain cell lineages – and affecting their pluripotency during the early stages of differentiation. In this particular study, researchers investigated the initial stages of the stem cell’s lineage and were able to identify several genes that controlled the growth phase – providing new insight into the early events of lineage commitment.
Another group was interested in discovering new stem cells for use in research and regenerative medicine due to the limitations of the current stem cells. The researchers created a way of culturing cells from the absolute earliest stage of development where the few remaining cells still retained their totipotency – the ability to produce all cell types. Their hypothesis was that these cells could be less programmed than embryonic stem cells and replicated using a special growth condition to inhibit the key development signals that would normally remove their totipotency. Beyond all of these scientific developments, the possibilities within adult stem cells become virtually limitless.
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