Genetics Embryonic Stem Cells Embryonic

Genetics

Embryonic Stem Cells

Embryonic stem cells come from embryos. The majority of embryonic stem cells are taken from embryos that are produced from eggs that have been fertilized in an in vitro fertilization clinic. They are then donated for research purposes with informed permission from the donors. The stem cells are never taken from eggs that have been fertilized in a woman's body. The embryos that provide the stem cells are usually four or five days old and are an empty microscopic ball of cells known as the blastocyst. "The blastocyst is comprised of three structures: the trophoblast, which is the layer of cells that surrounds the blastocoel, a hollow cavity inside the blastocyst; and the inner cell mass, which is a group of cells at one end of the blastocoel that develop into the embryo" (Stem Cell Basics, 2009).

Producing cells in the laboratory is called cell culture. Human embryonic stem cells are secluded by moving the inner cell mass into a plastic laboratory culture dish. The dish includes a nutrient solution called culture medium. The cells split and extend across the surface of the dish. The inside of each culture dish is typically covered with mouse embryonic skin cells that have been treated so they can not divide. This layer of cells is known as the feeder layer. The mouse cells are put on the bottom of the culture dish in order to give the inner cell mass a surface onto which they can stick. The feeder cells give nutrients to the culture medium. Researchers have developed ways to grow embryonic stem cells devoid of mouse feeder cells. This is major scientific progress because of the risk that viruses that might be in the mouse cells may be conveyed to the human cells (Stem Cell Basics, 2009).

The sequence of making an embryonic stem cell line has been found to be inefficient. Because of this lines are not formed every time an inner cell mass is placed into a culture dish. If the plated inside cell mass cells survive, divide and multiply to the pint that the dish is crowded, they are then removed gently and put into several other culture dishes. The process of re-plating or sub-culturing the cells is repeated many times and for many months. Each cycle of sub-culturing the cells is known as a passage. Once the cell line is founded, the original cells tend to produce millions of embryonic stem cells. "Embryonic stem cells that have reproduced in cell culture for six or more months without differentiating, are pluripotent, and appear genetically normal are called embryonic stem cell line. At any stage in the process, groups of cells can be frozen and shipped to other laboratories for further culture and experimentation" (Stem Cell Basics, 2009).

At many different times during the process of producing embryonic stem cell lines, scientists test the cells to see if they are indeed displaying the basic properties that make them embryonic stem cells. This practice is called characterization. Scientists who study human embryonic stem cells have yet to be able to settle on a standard series of tests that measure the cells' fundamental properties. Yet, laboratories that grow human embryonic stem cell lines use quite a few kinds of tests that include:

Growing and sub-culturing the stem cells for many months. This guarantees that the cells are able to have long-term growth and self-renewal. Scientists look at the cultures using a microscope in order to see if the cells look healthy and have remained undifferentiated.

Using precise techniques to determine the existence of transcription factors that are typically produced by undifferentiated cells. Two very important transcription factors are Nanog and Oct4. Transcriptions factors assist in turning genes on and off at the correct time. Both Oct 4 and Nanog are connected with maintaining the stem cells in an undifferentiated state which consist of the ability for self-renewal.

Using exact techniques to determine the occurrence of particular cell surface markers that are typically created by undifferentiated cells.

Investigating the chromosomes under a microscope. This is used in order to figure out whether the chromosomes are damaged or if the number of chromosomes has changed. This test does not detect genetic mutations within the cells.

Determining whether the cells can be re-grown, or sub-cultured, after freezing, thawing, and re-plating.

Analyzing whether the human embryonic stem cells are pluripotent. This is done by allowing the cells to differentiate spontaneously in cell culture, manipulating the cells so they will differentiate to form cells characteristic of the three germ layers or injecting the cells into a mouse with a suppressed immune system to test for the formation of a benign tumor called a teratoma. Because the mouse's immune system is covered up, the injected human stem cells are not cast off by the mouse immune system and scientists can watch growth and differentiation of the human stem cells. Teratomas characteristically have a mixture of many differentiated or partly differentiated cell types which is a sign that the embryonic stem cells have the ability to differentiate into multiple cell types (Stem Cell Basics, 2009).

If embryonic stem cells in a culture are nurtured under the right conditions, they can remain undifferentiated or unspecialized. If on the other hand cells are permitted to clump together in order to form embryoid bodies, they will start to differentiate. They can then form muscle cells, nerve cells, and many other human cell types. Although impulsive differentiation is a good sign that a culture of embryonic stem cells is healthy, it is not a very efficient way to produce cultures of specific types of cells. In order to create cultures that contain specific types of differentiated cells like heart muscle cells, blood cells, or nerve cells, scientists have to manage the differentiation of the cells. They do this by altering the chemical make up of the culture medium, modifying the surface of the culture dish, or adjusting the cells by putting in specific genes. Over the years, scientists through experimentation have set down some basic procedures for the directed differentiation of embryonic stem cells into specific cell types (Stem Cell Basics, 2009). It is thought that if scientists can dependably manipulate the differentiation of embryonic stem cells into specific cell types, they may be able to use the resulting, differentiated cells to care for certain diseases in the future. "Diseases that might be treated by transplanting cells generated from human embryonic stem cells include Parkinson's disease, diabetes, traumatic spinal cord injury, Duchenne's muscular dystrophy, heart disease, and vision and hearing loss" (Stem Cell Basics, 2009).

One of the most exciting areas in medicine is the prospective use of stem cells for treating a mass of congenital, developmental, or degenerative diseases for which there are presently no cures. Cell replacement approaches are predominantly relevant in tissues and organs that have little capacity to repair themselves. One such organ is the brain. Nerve cells have been identified as being very limited in their capacity to regenerate themselves following damage or disease, and the adult brain and spinal cord appear to have a very limited ability to produce new neurons. This is often why recovery is limited when the nervous system has been damaged. The objective of cell replacement is to come up with therapies that use stem cells that are first induced into a specified cell of choice and then transplanted into patients in order to replace damaged or non-functioning cells. It is thought that the replacement and integration of lost cells will be able to restore functions and behaviors that have been damaged by the disease (Human Embryonic Stem Cells, n.d.).