Fargo Moorhead LIFE Coalition
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What is a cell?
A cell marks the boundary between the living and the non-living. The molecules that serve as food for a cell and the organic molecules that make up a cell are not alive. However, working together in a highly organize manner, chemical and electrical processes enable cells to take in energy in the form of food and water to become self-sustaining, capable of responding to stimuli and reproducing themselves. This is life. Stopping these cellular processes causes death, that is, the reversion to a non-living state, were response to stimuli and reproduction are absent. While the human body contains many types of cells, all cells contain the same components. Working from the outside in, a cell is surrounded by a membrane, called a plasma membrane. Under a microscope, you would see that a cell is rounded in shape, like a tiny pill. Inside is a liquid called cytoplasm. Suspended in the cytoplasm are minute bodies called organelles. These structures process chemicals and molecules to form the specialized functions of the cell. Also in the liquid along the wall of the membrane is the nucleus, which stores the genetic information needed to direct these processes.

Diagram of a human cell

In an interview with William L. Todt, associate professor of biology at Concordia College, Moorhead, he explained how the cell works, comparing it in function to a auto shop.

"Imagine an automobile repair shop," he said. "The mechanic's manual contains the information, diagrams and directions on how to put the car together. This is the function of the nucleus. It contains the genetic codes."

The mechanics, the tools, the electricity, the nuts and bolts, the parts, are the material and energy needed to put the car together according to the directions, he explained. This is the function of the cytoplasm and the organelle. Organelle such as the Golgi complex and the endoplasmic reticulum are like cubicles where molecular processes and assembly take place.

The garage itself is the building where all this goes on, and that is the function of the surrounding membrane, that is, the shell, called the plasma membrane. It protects and encloses, plus lets molecules in and out.

What is an egg?
An egg is the female germ cell that contains all the genetic information of the mother in the nucleus, surrounded by a cell membrane. Sperm is the male germ cell.

Human egg cell

When the sperm unites with the egg through fertilization, an embryo is the result. However, the egg is also a kind of magic room, for if you take the original nucleus (unfertalized) out of that egg shell and put in a skin cell and give it an electrical zap, the egg environment will regress the skin cell to a stem cell, producing a clone of the donor nucleus. If implanted in a womb, a living clone would be produced.

What is an embryo?
An embryo created either in vivo or in vitro, that is, either in the body or in a laboratory, conventionally involves the fertilization of a female egg, which is a single cell, by a male sperm, which is another single cell. Here is how it begins. Once the sperm unites with the egg, a zygot is formed. While this is a combination of two cells, it is, itself, one cell.

Formation of the blastocyst

A zygot has half the chromosomes of the mother and half the chromosomes of the father united in a single cell and is capable of forming a new, unique human being, that is, a son or a daughter.

As this cell divides, it produces other cells with the same genetic information. As these cells continue to grow, a microscopic hollow ball filled with liquid is formed called the blastocyst. The outer membrane, the shell, of this ball is called the trophoblast. This outer membrane will become the placenta. The blastocyst is an embryo at its earliest stage.

Resting on the inside wall of this ball is a clump of other cells. These cells are the stem cells. Eventually, these stem cells will differentiate into distinct body parts, becoming the fetus.

Human embryo four weeks after conception

It is a marvelous world of astounding complexity, all working together to produce a unique life that will some day, if all goes well, be capable of living independently as a human being.

Shortly after fertilization, the embryo travels down the oviduct, a tube, into the womb and implants, that is, attaches to the wall of the uterus. Here it receives nourishment from the blood of the mother and grows into a fetus.

What are stem cells?
As mentioned above, stem cells are the inner cell mass that initially clings to the inside wall of the trophoblast. As the stem cells develop and differentiate, they initially flatten into a disk of cells, then start to fold in on themselves, eventually becoming the fetus.

Extracting the stem cells

But what happens when the stem cells are taken from the environment of the trophoblast by a researcher using laboratory instruments shortly after fertilization and cultured in Petri dishes? Instead of differentiating, they will replicate indefinitely, creating a stem cell line of millions of identical stem cells all with the same DNA information.

What is the trophoblast?
The trophoblast is the outer membrane of cells formed as the blastocyst, or the embryo, begins to grow. Inside it are the stem cells. Remarkably, these stem cells will not differentiate without the trophoblast. A trophoblast forms naturally following fertalization or when an egg is tricked through nuclear transfer and an electrical shock to develop into an embryo that is a clone.

What is differentiation?
The embryo grows by a process called differentiation, which is not well understood. Differentiation produces various cell types, about 210 different kinds, that form the organs, tissue and nerves of the body, such as heart, skin, teeth, bones, hands, feet, brain, spine and on and on. But DNA, specifically the 25,000 genes identified by the Human Genome Project, by themselves do not govern differentiation. If they did, human beings would start developing in Petri dishes from stem cells. DNA is not destiny. Instead, genes themselves need instructions for what to do, and where and when to do it. A human liver cell contains the same DNA as a brain cell, yet somehow it knows to code only those proteins needed for the functioning of the liver. Those instructions are found not in the letters of the DNA itself but on it, in an array of chemical markers and switches, known collectively as the epigenome, that lie along the length of the double helix, a spiral of DNA information. These epigenetic ("epi" Greek for "over, above" plus "genetic") switches and markers in turn help switch on or off the expression of particular genes, thereby regulating their function. Think of the epigenome as a complex software code, capable of inducing the DNA hardware to manufacture a variety of proteins, cell types, and, in the end, individuals.

What is induction?
Differentiation is governed in part by environmental factors, including spatial factors. The process by which a chemical or a tissue influences the development of another tissue is called induction. As the cells grow in number, they find themselves in different positions. Somehow, the cells can sense where they are in relation to other cells and begin to turn on or off certain genes, which make them more specialized.

As the inner cell mass grows, it begins to flatten into a disk, which is composed initially of two layers of cells, the ectoderm, the top surface of the disk, which will later become the nervous system and the skin, and the endoderm, the bottom portion, which will become the digestive and respiratory tracts and associated organs. The disk elongates and a streak appears down its center, which folds in on itself, becoming the mesoderm, developing into the skeleton and muscles.

As mentioned, induction is part of the process that governs this growth, with position of the cells inducing organ formation. In other words, cells develop in relation to other cells. For instance, an outgrowth of the brain induces a covering of tissue to thicken and develops into the lens of the eye. The lens induces an optic cup, where the retina develops and the optic cup in turn induces formation of other eye parts.

Cells evidentially communicate with other cells as they grow. For cells to grow properly, they must be in an environment compatible to their development. Cells in a foreign environment grow in an unregulated way. For example, researchers injected the muscle of a mouse with human embryonic stem cells. What they got was a tumor filled with a disorganized collection of human teeth, gut, hair, skin, muscle, bone, cartilage, lung tissue and neural cells.

To date, no one has yet demonstrated any in vivo reconstitution of an organ's function in either humans or experimental animals with cells derived from human embryonic stem cells. In fact, embryonic stem cells in tissue culture give rise to a mixture of cell types all at once. The biochemical, tissue-culture, and molecular-biology techniques to control and limit differentiation require much further investigation. (Stem cells and the future of regenerative medicine 2002, p.35)

What is an embryonic stem cell line?
Embryonic stem cells, as their name suggests, are derived from embryos. Specifically, embryonic stem cells are derived from embryos that develop from eggs that have been fertilized in the laboratory outside of a woman's body. The stem cells are the mass of cells found inside the blastocyst.

Stem cells in Petri dishes

Researches remove these cells, about 30 in number, and place them in plastic laboratory culture dish that contain a broth. The cells divide and spread over the surface of the dish. Eventually, they grow into millions of cells and are transferred from one dish to many other dishes, frozen, and shipped to other research labs for experimentation. They do not differentiate, lacking the trophoblast.

What are adult stem cells?
Adult stem cells are rare and are found not in embryos, but in mature tissues. Their function is to repair damaged tissue. Methods of expanding their numbers in a cell culture have not been worked out. Adult stem cells are not cultured, but individually harvested from donors using chemical extraction and other methods.

What is transplant rejection?
Transplant rejection occurs when a transplanted organ or tissue is not accepted by the body of the transplant recipient. This is explained by the concept that the immune system of the recipient attacks the transplanted organ or tissue. This is expected to happen, because the immune system's purpose is to distinguish foreign material within the body and attempt to destroy it, just as it attempts to destroy infecting organisms such as bacteria and viruses.

Immunosuppressive drugs are used to treat patients with transplanted organs to prevent rejection of the transplant. However, these drugs have the potential of reducing the immune response of the patient, making that patient more susceptible to disease, such as cancer.

One of the major reasons motivating research on cloning is that theoretically, if tissue cloned from a patient was transplanted into that same patients, the tissue would not be viewed as foreign and would thus not be rejected, avoiding triggering the immune rejection response.

What is a clone?
A clone is an identical copy of another creature, having the same DNA. In nature, identical twins are clones. Clones can be created artificially by a process called "somatic cell nuclear transfer." In genetics and developmental biology, somatic cell nuclear transfer (SCNT) is a laboratory technique for creating a clonial embryo, using an ovum with a donor nucleus. It can be used in embryonic stem cell research, or, potentially, in regenerative medicine where it is sometimes referred to as "therapeutic cloning." It can also be used as the first step in the process of reproductive cloning.

In SCNT the nucleus, which contains the organism's DNA, of a somatic cell (a body cell other than a sperm or egg cell) is removed and the rest of the cell discarded. At the same time, the nucleus of an egg cell is removed. The nucleus of the somatic cell is then inserted into the enucleated egg cell. After being inserted into the egg, the somatic cell nucleus is reprogrammed by the host cell. The egg, now containing the nucleus of a somatic cell, is stimulated with a shock and will begin to divide. After many mitotic divisions in culture, this single cell forms a blastocyst (an early stage embryo with about 100 cells) with almost identical DNA to the original organism.

Somatic cell nuclear transfer is done by taking out the nucleus of an unfertilized egg from a sheep, for instance, and replacing it with the nucleus from a somatic, that is, body cell (usually a skin cell or muscle cell) of another sheep, then zapping it with an electrical charge, stimulating it to divide and grow into a blastocyst, that is, an embryo.

It can then either be transplanted into the womb of a mother sheep (which is called reproductive cloning) and wait for it to be born. Or one can allow the clonal embryo to grow in the laboratory for several days, then destroy it, to harvest the embryonic stem cells so as to produce a custom-made stem cell line, identical to the genetic structure of the animal from which the original somatic cells were taken. This later method is called “therapeutic cloning.”