Structural Biochemistry/Nucleic Acid/DNA/Transgenic Animals

Transgenic animal are animals that have had foreign genes from another animal introduced into their genome. A foreign gene (such as a hormone or blood protein) is cloned and injected into the nuclei of another animal’s in vitro fertilized egg. Cells are then able to integrate with the transgene, and the foreign gene is expressed, upon which the developing embryo is surgically implanted in a surrogate mother. The result of this process, if the embryo develops, is a transgenic animal housing a particular gene from another species.

Applications of transgenic technology are for example, improving upon livestock, such as higher quality wool in sheep, or increasing the amount of muscle mass of an animal so that it can produce more meat for consumption. Conversely, transgenic animals can also be utilized for medical purposes such as producing human proteins by inserting a desired transgene into the genome of an animal in a manner that causes the target protein to be expressed in the milk of the trangenic animal.

Another example is one that involved mice. Normal mice have the capability to not be infected by the polio virus. They do not have the cell surface molecule that is required as a receptor for polio, unlike humans, who do have this receptor. However, the polio receptor gene can be injected into a mouse, thus developing a transgenic mouse. This allows the mouse to now be successfully infected by the polio virus, and display the similar symptoms that are displayed in humans who are affected by the polio virus.

The most common studies that are currently going on with transgenic animals involve animals, such as the rhesus macaques. These animals contain the human gene of the Huntington’s disease. This allows scientists to research options that can provide a cure to Huntington’s or at least a better treatment option. Other animals, such as mice or those that contain human stem cells, are used to create medicine and treatment options for diabetes, strokes, and blindness.

The human genome project has also been of great help in the role of transgenic animals. With the newfound discovery of the DNA sequence of the human genome, scientists can now study the genes that are involved as drug targets, which can help provide them with the ability to mark the appropriate gene that can aid in providing the cure to any certain disease that they are studying.

The expression of a transgene can also be engineered to take place in plants, such as obtaining the bio-luminescent gene that gives fireflies their glow in the dark ability, and introducing it to a plant.

Transgenic Animals Countless Benefits to Humanity

Three of the most widely-used reasons for producing transgenic animals for the benefit of human welfare are agriculture, medical and industrial.

Agricultural Applications

Farmers have always wanted to have the best breed for any type of animal and to have the best traits that it can possible have. The normal way of breeding animals can potentially take up a lot of time and is not entirely efficient. With new advances in technology, selected characteristics can be developed in species with a lot less time and more accuracy.

Not only are animals produced more efficiently, the quality of the animals are enhanced as well. Some examples include having cows create milk with lessened milk content and sheep that produced a lot more wool.

Also, with these new qualities in animals they must be protected. Scientists are researching on creating animals that are resistant to particular diseases and to enhance the two reasons stated above.

Medical Applications

Animals that have their genes modified to show disease symptoms, may be studied and cure could possibly be contrived in the near future.At Harvard, scientists created a transgenic mouse also known as OncoMouse® or also known as the Harvard mouse which allows it to carry genes that can enhance the development of a variety of cancers that are found in humans.

Xenotransplantation will play a major role in the medical industry in the future. It is the transplantation of living cells, tissues or organs from one species to another. Due to worldwide shortages of organs, advances in gene manipulation of animals can alter their organs to become susceptible to humans. For example, Transgenic pigs may play a major role in the transplant of organs to humans. Because Pig and human organs are closely related, there is a possibility to use pig organs for transplants. However currently, a pig protein inhibits the human body’s immune system acceptance of the organs. If animals such as Pigs can have its protein successfully supplanted by a human protein can be used to meet a major need- transplant organs such as the hearts, liver, or kidneys. It can also be applied to bringing about refined drugs in the pharmacy industry and nutritional supplements. An example is insulin and anti-clotting factors of blood can soon be extracted from milk of transgenic animals such as goats, sheep, cows. This milk being the source of importance is undergoing major research to create a type that will be able to treat diseases such as phenylketonuria or cystic fibrosis.

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Human Gene Therapy, [1]

Human gene therapy is another medical application that is gaining wide acclaim. In essence, it is the transfer of genetic information into patient tissues and organs. As a result, diseased defective copies of genes can be eliminated or their normal functions rescued. Moreover, the procedure can provide new functions to cells. For Example, to combat cancer and other diseases, the insertion of a gene that causes the production of immune system mediator proteins can be introduced. By this therapy, countless genetic disease could have potential cures further down the road. There are two paths to Gene therapy. The first path is direct transfer of genes into the patient. The second path is the use of living cells as vehicles to transport the genes of interest. These two paths both have certain advantages and disadvantages. Direct gene transfer is the most simplistic way of administering the gene of choice. There are two methods to direct gene transfer. The first method is the process in which genes are delivered via liposomes or other biological microparticles into patient’s tissue or bloodstream. The second method of the introduction of genes is using genetically-engineered viruses, such as retroviruses or adenoviruses. However, due to biological safety concerns, viruses must first be altered so they are not infections before introduction. However, due to the simplicity of the direct gene transfer method, there are major weaknesses. For example, it does not allow for the control of where the therapeutic gene will insert. The transferred gene will either randomly insert itself into the patient’s chromosomes or remain unintegrated in the targeted tissue. Moreover, the target tissue may not be easily accessible for direct gene application of the therapeutic gene. The second method of gene therapy is the use of living cells to deliver the therapeutic gene. This method is very complex compared to the direct gene transfer method. There are three major steps to this method. The first step is cells from the patient are isolated and propagated in vitro. The second step is the introduction of the therapeutic gene into these cells using methods similar to the direct gene transfer. The last step is the genetically modified cells are returned to the patient. The advantage of using gene transfer vehicles is, in the laboratory cells can be manipulated more accurately and precisely than in the body. In addition, some of these cells are able to continually propagate under laboratory conditions before reintroduction into the patient. Moreover, some of these cells types have the ability to localize to particular regions of the human body, for example, hematopoietic (blood-forming) stem cells can return to the bone marrow upon reintroduction in to the body. This action can be very useful for applying the therapeutic gene which has regional specificity. However, a major disadvantage is the biological complexity of the living cell’s environment. The isolation of a specific type of cell requires not only extensive information of its biological markers, but also knowledge of the requirements for that cell type to stay alive in vitro and continue to divide. Unfortunately, there are many cells types with unknown information to their specific biological markers. Moreover, many normal human cells cannot be sustained in the lab for long periods of time without amassing deleterious mutations.

Industrial Applications

Animals that have transgenes have been produced to for testing on chemical safety as these animals are sensitive to toxic things. Also, these transgenic animals may produce something that can be utilized in biochemical reactions. Microorganisms have been structured to be able to produce enzymes that can make major reactions speed up.

Production of Transgenic Animals

The production of transgenic animals is taking the genome, the genetic makeup of the organism and introducing foreign genes into that organism. These insertions of genes are known as transgenes. Most importantly, these foreign genes must be transmitted through the germ line of the organisms. As a result, every cell, including the germ cells, whose function is to transmit genes to the organism’s offspring, contains the same change in genetic material.The predominant method of creating these transgenic animals is the use of DNA Microinjection. However, producing these type of transgenic animals is hardly deemed a success as DNA insertion is arbitrary and success rate very low. The offspring is what's studied for this new transgenic gene. But the ability to produce these type of offspring that is successfully carrying the gene is extremely difficult.

Scientists may produce transgenic animals is three main ways: DNA microinjection, retrovirus-mediated gene transfer and embryonic stem cell mediated gene transfer.

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Transfer of desired gene into mouse via microinjection, [2]

DNA microinjection

Technique summary

The first animals to be experimented with DNA microinjection was the mouse. DNA Microinjection is the transfer of a desired gene into the pronucleus of the reproductive cell. This cell is first cultured in vitro. Then reaching to a specific stage or threshold of the embryonic phase, it is then transmitted into the recipient female.

Technical Explanation

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Retrovirus mediated Gene transfer, [3]

The pipets for this technique must be created especially from glass that are extremely thing and a pipet puller as well as a micro-forge. It must be absolutely flat at the tip or there will be impedance when injecting into the embryo. The specification of the DNA injection pipet should have an internal diameter of about 1 µm or even less. When performing this technique gloves that are covered with talc should be avoided as the power has the potential to clog the pipets and could lead to the failure of the embryos. The embryo that is working with should be put in very low magnification. Using the pipet, with ease suction the embryo into the end and let it stay there. The tip of the pipet is brought to exactly where the pronucleus is and then it is punctured through the cell membrane and into the cytoplasm area. It is often hard to see if the pipet tip has gone through into the pronuclear membrane. The only safe bet in judging if it was transferred successfully is to glance at the pronucleus to see if it swells up and its size in volume amounts to around 1pl. After injection it is then moved to the far end of the dish so that the next one may be done as well. When a bundle of embryos are complete, it is left for incubation and then evaluation for a duration of time. The embryos that are viable will then be transmitted to a female's oviduct and then utilized.

Retrovirus-mediated gene transfer

Retroviruses are used as vectors to transfer genetic material in the form of RNA rather than DNA. It is the transfer of genetic material into the host cell, resulting in a chimera, a organism that has various genes aside from its own. These chimeras are inbred for as many as twenty generation until homozygous offspring are formed, carrying two copies of the same transgene in all of its cells. This has been proven successful in 1974, when a virus was used as a vector into embryos of mice. They showed the desired transgene.

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Embryonic stem cell mediated gene transfer, [4]

Embryonic stem cell mediated gene transfer

The technique involves isolation of the totipotent stem cells from embryos(stemcells that can develop into any type of specialized cell). The desired gene is inserted/transfer into the stem cell. These stem cells containing the desired DNA of interest are now incorporated into the host's embryo. Thus resulting in a chimeric animal. A major benefit of this technique is that it may test the transgenes on the molecular level, which essentially saves ample time and using this technique one would not have to wait for living offspring.

Stem Cells (in Further Detail)

What exactly are stem cells?

Stems cells are now a hot topic for research because of their seemingly endless potential. They are cells that may develop into numerous different categories of cells in the body during the beginning stages of life and also during the growth stage. Stems cells can also be utilized as an internal repair system, basically dividing incessantly to restock the cells under damage and repair until it reaches back to equilibrium and for the duration of the organism's life span. As stem cells divide, each has the opportunity to choose between sticking as a stem cell or become more specific- one with a specialized function, examples including liver cell, a white blood cell, brain cell, etc.

How are stem cells set apart from other types of cell?
There are two primary properties that are used to do this. The first aspect is that stem cells are initially unspecialized cells and may regenerate through cell division, and even at times after prolong periods of time without activity. Another aspect is that under right, specific physiological conditions can be promoted to turn into either tissue or certain cells of organs and with distinctive abilities. Examples of when stem cells are maximized for their repair function are in organs, bone marrow, gut marrow, where they constantly divide to restore injured cells or ones that have been heavily used.

In the past, researchers mainly worked with two categories of stem cells which were from both humans and animals. The two that were worked on were embryonic stem cells and somatic stem cells, which can also be called adult stem cells. The first embryo cells came from mouse as described above, which occurred around 1981. The human embryonic stem cells were made for reproduction and was made possible through the intense research done with the mouse embryos. Recently, there has been a third category of stem cells known as induced pluripotent stem cells(iPSCs). These cells are unique because they are cells of adults that can be reconditioned by gene modifications to be a stem cell.

Why are stem cells valuable for living organisms?
Typically in blastocysts, which are embryos of only 3–5 days aged, the cells on the inside will turn into the cells for all of the body of that living organism, even specialized cells and organs including the skin, heart, lung, reproductive cells-sperm and egg, and different tissues. Within the tissues of adults including bone marrow and muscle, these stem cells have the ability to replace the cells that are damaged, affected by disease, or simply just used.

Research in the stem cell arena, has continued to add new insights to the development of organisms from cells and the repairing mechanism of affected cells. Stem cells may also be utilized to help select for new drugs to be brought to market and better understand not only cell developments but also the irregularities that induce defects in the infants of organisms.

Special characteristics of stem cells
Stem Cells are very unique and set apart from other cells of the body. All types of stem cells will have 3 defining characteristics- able to divide and replenish themselves for long duration of time, not specialized, able to be turned into numerous different types of cell types. For each of these properties, further depth analysis will be explained below.

The first property discussed was stem cells ability to divide and replenish themselves for a long duration of time. Typically cells of muscle or nerve do not duplicate by themselves, but stem cells have the ability to do this and also done ample times. Stem cells replicated countless times in the laboratory times for months at a time may result in millions of cells. If the cells can go on for a long time and not be specialized just like the parents, these cells are able to perform self-renewal for the longterm. Two sources of profound interest under study about this self-renewal for the longterm is how embryonic stem cells can replicate for an entire year in the laboratory and not differentiate but usually non-embryonic stem cells are not capable of this and which aspects of organisms are the ones that are source of regulation of stem cell replication and this self-renewal.

Finding out how the regulation of stem cells is performed for stem cells normal development may assist in finding out the reasoning for cancer through irregular cell division. This could also lead to more efficient growth embryonic and non-embryonic stem cells performed in the laboratory setting. Having stem cells that continue to stay as unspecialized result from special conditions. These special conditions are set up from signals in the cells that induce the stem cells to replicated and stay as unspecialized.

Stem cells are ones that are not specialized. Since they are not specialized, they are incapable of doing any specialized tasks that could occur in specific tissues or organs. As a result, stem cells cannot work collaboratively with other cells to perform organized tasks such as being a carrier of oxygen molecules throughout the body such as red blood cells. But what is unique about stem cells is their potential to be made into specialized cells such as nerve cells, brain cells, or muscle cells.

Stem cells have the capability to be made into specialized cells. The progression of stem cells that are not specialized being turned into ones that are specialized is known as differentiation. The differentiation process have multiple steps and the progression through these steps increases specialization. Many factors help to control this progression. Signals that both inside and outside of the cell help promote the stem cells through each stage. Outside signals include being in close, touching proximity of nearby cells, chemicals that are given off by other cells, and the presence of specific molecules in the immediate environment. Inside signals are managed by genes present on the DNA that tell it exactly what to do. Understanding the regulation of these stem cells can help to grow cells or even tissues to help in selecting for drugs and cell therapy, which is what makes stem cells so special and a primary source of research.

Different types of stem cells

Embryonic stem cells
These type of cells come from embryos. A major portion of these types of cells come from eggs that are fertilized in vitro or in the laboratory setting and then given to labs so that research may be done on them. The embryos from the human stem cells are usually about 4–5 days aged and are in the blastocysts form, which essentially is a hollow ball of cells. The blastocysts have a total of three structures including the trophoblast, embryoblast or pluriblast, and blastocoel. The trophoblast is a layer that surrounds the blastocoel. The hollow cavity of the blastocyst is the blastocoel and the embryoblast is mass of cells that will turn into defined structures of the fetus.

How are embryonic stem cells identified?

While creating embryonic stem cells, there are various checkpoints to test if the cells have the right properties that allow it to be called embryonic stem cells. This is also known as characterization. There is not a universal test agreed to always be used to mark embryonic stem cells but there are various tests that can be used. The first one that can be used is to grow these stem cells for a number of months. This proves that the cell can do long-term growth and self-renewal. The cells are put under a microscope and observed to see that it is in good condition and still have not differentiated. A second test that is to determine transcription factors that are characteristic of cells that are not differentiated. Specific transcription factors to look for are Nanog and Oct4. Essentially what transcription factors do is aid in turning genes either off or on when needed, which is very integral in cell differentiation and development of embryos. Nanog and Oct4 help to keep the stem cells to be undifferentiated. A third test is to use specific techniques to look for cell surface markers that undifferentiated stem cells will give off. A fourth test is to look at the chromosomes using a microscope and to diagnose if there is damage or if the quantity of chromosomes is different. A 5th test is to see if the cells can be grown again after putting it in the freezer and then allowing it to thaw. The last test which is the 6th one is to test if these human embryonic stem cells are pluripotent. This may be done by permitting the cells to instinctively differentiate in the laboratory, conducting the cells so that it will form a cell that consists of three germ layers, or injecting the cells into a mouse that has an impaired immune system to test for the development of teratoma, a tumor that is benign. The growth of the injected stem cells and its differentiation may be observed since the immune system of the mouse does not reject it. Encompassed in the tumor cells is a combination of differentiated or somewhat differentiated kind of cells, showing that embryonic stem cells have the ability to differentiate into other different types of cells.

How does differentiation of embryonic stem cells occur?
When embryonic stem cells are kept under the right conditions, they can be kept in the unspecialized state. When cells are permitted to aggregate and form what is called embryoid bodies, spontaneously differentiation occurs. These cells are able to form numerous different types of cells. This does show that this sample of embryonic stem cells is good condition, however this method is not efficient in creating certain cell types.

Mouse embryonic cells that are directed in differentiation, photo by Terese Winslow, [5]

In order to generate cultures of specific types of differentiated cells such as blood cells or brain cells, is done by controlling the differentiation of these embryonic stem cells. Components to modify are the different chemicals the culture medium is made of, the surface of the culture dish, or even the cell themselves by giving them specific genes. After a long time of trial and error there have been some standard protocols established for this directed differentiation to certain cell types to occur. If this directed differentiation of embryonic stem cells is done successfully, they can be used to treat certain diseases which include Parkinson's disease, Duchenne's muscular dystrophy, heart disease, vision loss and traumatic spinal cord injury.

Adult stem cells
Adult stem cells are thought to be undifferentiated type of cells, located with differentiated cells either in a tissues or organs that can revitalize itself and may differentiate to give either some or all of the primary specialized types of cells of an organ or tissue. The main job of adult stem cells in organism are to sustain and restore the tissues where they are located. Unparalleled to embryonic stem cells that are named according to location in which they are found, the stock of some adult stem cells in some tissues that are already mature are still being researched.

As more research is being conducted on adult stem cells, their presence is being found in many additional areas of tissue than ever before. This has opened up the possibility of these adult stem cells to be used as transplants. A widespread use of adult stem cells as transplants are for hematopoietic stem cells from bone marrow, which is blood-forming. It is now evident that stem cells do exist in the heart and the brain. The control of differentiation of these stems cells if done correctly it may be feasible to use them for transplantation therapy treatments.

Adult stem cells were first discovered in bone marrow, which contained two versions: hematopoietic stem cells and bone marrow stromal stem cells, which were discovered second. The stromal cells were small in number but had the ability to make everything including fat, bone, cartilage, and fibrous connective tissue.

Location of adult stem cells and their role?
Adult stem cells are actually located in numerous different organs and tissues which include bone marrow, brain, blood vessels, skin, teeth, heart liver, epithelium part of ovarian, and testis. Within each tissue, stem cells live in a particular area. In a lot of tissues, some stem cells comprise the outside layer of small blood vessel known as pericytes. Stem cells usually do not divid for long durations of time until prompted to for normal maintenance of tissues, after injury, or by disease.

Normally the number of stem cells in each tissue is small and once taken away from the body, their ability to divide becomes limited and duplicating large amounts of stem cells difficult. As a result, researchers are looking for improved ways to grow large quantities of adult stem cells in the laboratory so that specific ones may be created to target and treat diseases and injuries. Uses include to recreate bone from cells located in the bone marrow stroma, making cells that produce insulin to help treat diabetes of type1, and to rejuvenate heart muscles that were greatly impaired after a heart attack event.

Identification of adult stem cells

There are many methods to identifying stem cells. Researchers typically use several methods to identify the adult stem cells. One way it occurs is to tag the cells that are in living tissue with molecular markers and then look to see the produced specialized cell types. Another useful method would be to take the cells from a living organism, tag them in the laboratory and reinsert them into another organism to observe whether or not the cells recreate cells at their original tissue location.

One of the primary things that must be exhibited is that one adult stem cell will be able to produce an entire colony of genetically identical cells that can also create the correct differentiated cell types of that particular tissue. To produce these results experimentally and confirm that the cells are indeed adult stem cells is done through showing that it can create genetically identical cells or that the cells can remake the tissues after inserted into another animal or both of these.

Adult cell differentiation

Differentiation of Both Hematopoietic and stromal stem cells, photo by Terese Winslow, [6]

Normal differentiation
Adult stem cells are free to divide when called and can produce mature cells that have the same shapes, structure, role of that tissue in which it resides. Examples of this will follow. Hematopoietic stem cells will produce any type of blood cells including the b lymphocytes, T lymphocytes, natural killer cells, basophils, monocytes, red blood cells, etc. Mesenchymal stem cells actually produce a whole variety of cell types including bone cells, fat cells, cartilage cells, etc. Neural stem cells of the brain may produce neuron, astroyctyes, and oligodendrocytes. In the lining of digestive tract reside epithelial stem cells and they produce cells including goblet cells, enteroendocrine cells, absorptive cells, etc. The stem cells of the skin reside in the basal layer of the epidermis and produces keratinocytes, that provide the security layer.

Transdifferentiation
Particular adult stem cells can differentiate into other types of cells of other organs or tissues than it's predicted type, such as heart muscle cells differentiating into brain cells. This type of differentiation is better known as transdifferentiation. This occurrence in human beings is still not fully proven. Some possible explanations for this type of differentiation being observed could be the junction of this donor cell with the recipient. Another explanation could be that these injected stem cells give off factors that promote that other organism's own stem cells to initiate the repair mechanisms. When transdifferentiation has been observed, it is only seen in small instances.

Scientists have proved that some adult cells can be remade into different cell types in the laboratory using precise gene alterations. This can prove to be a way to remake cells into the other ones that have been injured or eliminated because of diseases. In diabetes, the cells that produce insulin or beta pancreatic cells can be recreated by reprogramming other cells in the pancreas. These recreated cells were very close i appearance and shape to the actual beta pancreatic cells. These reprogrammed cells when put into mice did improve the regulation of the sugar levels in the blood even though the mice had nonworking pancreatic beta cells.

Adult somatic cells can be reprogrammed to mimic embryonic stem cells through the presence of genes of embryos, and these types of cells are known as induced pluripotent stem cells iPSCs. Through iPSCs cells can be introduced that receptive by the donor and will not be rejected, which is important when recreating new tissue. However, iPSCs are still under study until they can produced to entirely only stick to its designated cell type.

Similarity among stem cells
Both human embryonic and adult stem cells have similarities and its differences in relation to using for regenerative therapy or repairing already damaged tissue and cells. A primary difference between adult stem cells and embryonic is the amount of different abilities that each is capable and the specific kind of differentiated cell types they will turn into. Embryonic stem cells can actually turn into all the different type of cells in the body because of their pluripotent nature. Adult stem cells are very specific and so limited to only differentiating into the type of cells of their original tissue.

A noteworthy difference is that embryonic stem cells can be grown with great ease in the laboratory. Looking within mature tissues, the adult stem cells are limited in number so finding these cells may be difficult. Unlike embryonic stem cells, adult stem cells still do not have a way to be grown in the laboratory. This difference has a great impact as replacing cell mechanisms oftentimes requires an abundance of cells in order to work properly.

Moreover, the tissues created from either embryonic or adult stem cells may be different in probability of rejection rate post-injection or transplantation. Embryonic stem cells have not been researched too heavily yet as testing using cells from hESCs were only just now approved by the FDA(Food and Drug Administration). The adult stem cells and tissues that form as a result are presumed to be less probable to rejection post-transplantation. The success can be attributed to using patient's self cells to be duplicated in the laboratory and then induced to differentiate into a specific cell kind and then re-injected into that same very patient. Utilizing the adult stem cells and the tissue products from the patient's very own cells highly decreases the probably of rejection by the immune system. This proves to be a major benefit since only using immunosuppressive drugs can help fix this problem but then the drugs have side effects that come along as well.

Uses for stem cells

Using adult stem cells to repair heart muscle cells, photo by Terese Winslow, [7]

There are many uses for stem cells, especially in research and in clinic. Studying human embryonic stems cells will help give information about development of humans. The principal target is to pinpoint how undifferentiated stem cells become differentiated cells and then later to form organs and tissues. Gene regulation is imperative in this aspect. A lot of the most irregular activity in humans result from aberrant erroneous cell division and differentiation. New research has found that iPS cells show that specific factors are associated with genetic signaling and molecular signaling and introducing these into the cells in a proper manner to command these processes will need a special technique.

Stem cells of humans may be used to select for new drugs. These drugs can be tested to see that it is not damaging using these differentiated cells. A vivid example would be to use cancerous cells to select for drugs that could be anti-tumor. Environment of the drugs should be very similar in order to check if the drugs actually work and this can be done through having a precise command over where the differentiation of stem cells turn into.

Another widespread use of stem cells is to utilize them to create cells and tissues to repair damaged or disease tissue in cell therapy. These regeneration of cells and tissues can aid in treating disease such as Alzheimer's disease, stroke, heart disease, osteoarthritis, and spinal cord injury.

Checklist for successful transplant of stem cells
1) Duplicate in mass amounts and be able to produce enough quantities of tissue 2) Differentiate into wanted type of cells 3) Live to survive in recipient post-transplantation 4) Become integrated into the tissue in the proximity post-transplantation 5) For entire duration of organism's life- be able to correctly function 6) No detrimental effects on recipient

Ethical conflicts with stem cells?
The main concern with stem cells has to do with the human embryonic stem cells, which has created a lot of public interest and conflict. Stem cells that are pluripotent, or may become numerous different types of cells in the human body are created from human embryos that are some days aged. The major debate is of when does life technically commence and if embryos or even fetuses would be considered as such and also who has the power to decide on such an issue.

United States' position on stem cells
The Bush administration in 2001 offered federal funds for research on human embryonic stem cells if certain three criteria were met. However, President Barack Obama issued an Executive Order 13505 known as Removing Barriers to Responsible Scientific Research Involving Human Stem Cells on the 9th of March 2009. This allowed National Institutes of Health or NIH to take a different strategy on doing human stem cell research. Also this Executive Order essentially nullified both the Executive Order 13435 and the presidential statement that occurred on August 9, 2001.

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