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This short excerpt provides readers with basic information on what a stem cell is, basic characteristics, history as well as medical perspective on the subject. It will also include why stem are controversial in an ethical perspective.

== Stem Cells ==

Stem cells are undifferentiated, pluripotent and self-renewing cells that have the capability to differentiate into different types of cells such as nerve, cardiac, muscle, intestinal and liver cells. Stem cells either divide symmetrically or asymmetrically which determines a path for them.

Symmetric cell division results in two identical daughter stem cells while Asymmetric division results in the rise of a differentiated cell along with a stem cell. As differentiated cells move farther from the original pluripotent stem cell, its fate becomes more determined. There are two types of stem cells; Embryonic stem cells and Adult stem cells.

The former are found from the inner cell mass of a blastocyst, which is one of many states of development of a developing embryo, while the later is found from tissue systems that give rise to all three embryonic germ layers. These three embryonic germ layers are the endoderm, ectoderm and mesoderm. Stem cells have a very promising future in the world of medicine and could be used to treat many diseases that involve the skin, nerve or the pancreases and possibly even more.

Brief History
According to Leonardo M.R.Ferreira’s short article on the history and outlook on stem cells, he mentions that it is hard to pinpoint who exactly researched stem cells first but that the first two scientists that rigorously studied the properties of stems cells were Ernest McCulloch and James Till.

McCulloch and Till stumbled upon two very important characteristics of stem cells, as well as the existence of hemopoietic stem cells in the blood while investigating how ionizing radiation effected mammalian cells in mice. These two men were essentially treating mice that had been heavily exposed to radiation, and treating them with bone marrow cells.

The transplantation of bone marrow cells to mice with high exposure levels of radiation, resulted in lumps on their spleens which they later identified to be caused by a cluster of cloned cells from a single cell; this cell identified as a stem cell. The two characteristics that both scientists identified in stem cells were the ability to self-renew and their ability to differentiate.

Following McCulloch and Till came the first two scientists to identify, isolate and culture embryonic stem cells from the inner cell mass of a developing blastocyst of a mouse; Martin Evans and Matt Kauffman 1981.

== Sources == Embryonic stem cells are obtained by developing a zygote up to the blastocyst stage. The blastocysts is composed of two distinguishable parts that are visible upon examination;Trophoblast and the inner cell mass. The inner cell mass is the region where Embryonic stem cells are harvested and cultured to give rise to more embryonic stem cells.

It is important to mention that in order to stop the blastocyst from developing even further, scientists use what is called the Leukemia Inhibitor factor(LIF), essentially inhibiting differentiation. In addition to this very popular method of obtaining pluripotent stem cells, there are other methods used. Such methods include extraction from Embryonic Carcinoma cells, Embryonic germ cells as well as Induced pluripotent stem cells(iPSCs).

Out of all of these methods, the method of Induced pluripotent stem cells(iPSCs) are the only that are extracted from a tissue biopsy in a developed organism, such as a Human. iPSCs are amongst the most exciting type of stem cells derivatives because they are not as invasive as the former methods of cultivating stem cells and because it transforms cells that are already differentiated and reprograms them to an earlier stage of development. Dr.James Thompson and Dr.Shinya Yamanaka's labs made this happen by first comparing the similarities between a pluripotent stem cell and a fibroblast, which is a cell that makes up connective tissue and helps in the healing process if a person is wounded.

The similarities or "defined features" as Yamanaka describes and is seen in Nicole Zur Nieden's lecture on Induced pluripotent stem cells, are four markers that both embryonic and fibroblast cells share. Those four defining features are OCT3/4, SOX2, c-Myc, and K1f4. With this information, both Yamanaka and Thompson were able to convert fibroblasts into pluripotent stem cells by culturing fibroblasts and infecting them with a retrovirus. The key in the conversion process was in the retrovirus, which was specifically modified to over-express these "defined features" and to carry an antibiotic that would later sieve through the weaker cells and obtain the more potent ones that essentially took in the viral host.

These remaining cells would then be cultured and later change their phenotype to look more like a pluripotent stem cell. The final step in recognizing that these cells that were cultivated were in fact stem cells was to inject them into a blastocyst and implant them into the uterus of host female mice. This modification gave rise to a chimeric mouse, which was the final proof that the cells that were in fact cultivated, were in fact pluripotent stem cells. This was a huge accomplishment in the scientific community and a step forward to creating useful organs out of fibroblasts.

== Therapeutic use of hESC == The future of human embryonic stem cells (hESCs) is very bright as new discoveries and more research is being done on this matter. hESC could be used therapeutically by using a pluripotent stem cell and generating skin, nerve and pancreatic cells that could potentially be transplanted back into the patient. It is important to note that in order for the patient's body to accept and not reject the cells, the pluripotent stem cells being generated have to come from the patient him/herself.

This is done to decrease the chance of the needed skin, nerve or pancreatic cell from being rejected. In the research study, "A review of the emerging potential therapy for neurological disorders: human embryonic stem cell therapy", Geeta Schroff, Jyoti Dhanda Titus and Rhea Shroff concluded that hESC lines could be treated in various neurological diseases such as a Spinal Cord injury (SCI), cerebral palsy (CP) and Parkinson's disease (PD). One of the studies involved 40 patients with severe Parkinson's disease.

These patients were 34-75 years of age and were administered hESC dopamine derived neurons. The result showed that the cells in younger patients survived longer and provided more of a beneficial effect than the patients that were much more older. Although there is more information that we do not yet know, the future of stem cell therapy is on the rise and does have a place in the community of many scientists from researchers to doctors and everyone in between.