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4 125-126 procedures, 2 4 RNA interference tools, 4 54 rodent models, 4 61, 4 124-127 therapeutic uses, 2 73 vectors, 2 71, 2 72, 4 125-126 Gene therapy, 2 74-80 advantages, 2 83 antisense nucleotide tools, 1 29, 1 30-31 disadvantages, 2 77 disease targets, 2 74 ectopic expression toxicity, 2 74 gene targeting tools, 2 73, 2 81 genomics industry role, 2 124-125 germ line vs. somatic cell therapy, 2 80-81, 2 82-83 lipid vesicle vectors, 2 76-77 longevity of gene expression, 2 77, 2 81 patent...
Gene Therapy
Understanding the genes responsible for SCID has also led to an increased understanding of the genes involved in the overall development of the immune system. It has also helped to unravel the complicated signaling pathways between the cells of the immune system that control and define the immune response itself. There has also been another major benefit. The study of SCID has, in the past, aided in developing an effective program for bone marrow transplantation. Interleukin binds to its...
The Growth of Specialization
Previously, most publications put so little emphasis on science that they did not need a specialized reporter. More and more, though, news organizations regard scientific results as necessary information, part of the everyday reporting of news. After all, science and technology have radically altered the way we live. For example, consider the development of antibiotics and vaccines, nuclear weapons, computer technologies, lasers, and fiber optics. Advances in science and technology will...
Retroviruses and Cancer
Retroviruses are among several types of viruses that can induce cancer in the host organism. So-called slowly transforming viruses are exemplified by human T-lymphotropic virus (HTLV), which causes leukemia (a type of blood cancer) in humans. These viruses induce malignancy by a process called insertional mutagenesis. The initial event is thought to be retroviral integration near, and subsequent activation of, a cellular oncogene (c-onc). Examples of c-onc include genes for growth factors,...
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Within seventy-two hours, the zygote develops into the morula, the solid mass of blastomeres formed by the cleavage of the fertilized ovum (egg). After about three to five days in culture, the zygote has become a hollow ball of cells called the blastocyst. During normal embryogenesis, it is the blastocyst that is implanted in the endometrial lining of the uterus. While the embryos are in culture, problems in their development may become apparent. After embryos with...
Types of Polymerases
Prokaryotic organisms (Eubacteria and Archaea) have only one type of RNA polymerase. Eukaryotic organisms (animals, plants, fungi, and protests) have three types, called pol I, II, and III, and each transcribes a different set of genes. Pol I synthesizes RNA for the large subunit of the ribosome (the protein-making machinery of the cell), and one piece of RNA for the small subunit. Pol II creates messenger RNAs, which provide a template for protein synthesis. Pol II also creates numerous small...
Mechanisms of Functional Tumor Suppressor Loss
There are three main ways in which a cell can lose the functionality of its tumor suppressor genes. Chromosomal aberrations, such as balanced reciprocal translocations, can occur. In such translocations, two unlike chromosomes switch segments. The most common such aberration is the chromosome 11 and 22 t(11 22) (q23 q11) translocation. It occurs in 10 to 15 of every 10,000 newborns and is the most common cause of childhood leukemia. The chromosome 9 and 22 t(9 22)(q34 q11) translocation gives...
Viral Cancers
Infection with certain viruses can also result in cell transformation, stable genetic changes in the cell that result in disregulated cell growth and extended growth potential (immortalization). In animals, such virally induced cellular changes can result in cancer. This correlation was first made by Harry Rubin and Howard Temin in the 1950s, when they observed that Rous sarcoma virus, a retrovirus capable of inducing solid tumors in chickens, could also cause biochemical and structural changes...
Genetic Selection and Medical Motives
Ova and sperm can be genotyped so that particular genes or combinations of genes can be selected. While this is usually very expensive and not yet foolproof, success has been reported in influencing the sex of a child. Cells from early embryos can be removed for even more precise geno-typic determination and selection. Such selection has the potential of being more and more precise. Technology may even become capable of altering traits, as the genome becomes better understood. What kind of...
Types and Severity of Immunodeficiency Diseases
Disease severity can range from mild to fatal, depending upon what part of the immune system is affected. Immunodeficiency can originate in normal individuals as a consequence of chemotherapy, viral infections (such as AIDS, which is caused by the HIV virus), or as the result of other processes that prevent immune system function. When immunodeficiency occurs in this manner, it is called acquired. In contrast, immunodeficiency can also be inherited as a genetic mutation that prevents the normal...
Donor Gametes
One of the oldest and least controversial reproductive technologies is the use of donor sperm to overcome low sperm count on the part of the male or to avoid inheritance of some genetic condition that the male might pass on to his child. Donation is usually anonymous, but some characteristics of the donor are known. Ethical issues arising in sperm donation include the extent to which parents have the right to choose desirable characteristics in the genetic father of the child, and the right of...
Reverse Transcription and the Human Genome
When reverse transcriptase was first described, it was believed to be a peculiarity of retroviruses. However, researchers now know that reverse transcription also occurs during the replication of the DNA virus hepatitis B, and that RNA-copying DNA polymerases function within human cells. One of these host reverse transcriptases is telomerase, an enzyme that helps maintain chromosome ends. Other human reverse transcriptases are parts of endogenous retroviruses and retroelements, such as those...
Commercial Application
Transgenic microbes have many commercial and practical applications, including the production of mammalian products. A company called Genentech was among the earliest and most successful commercial enterprises to use genetically engineered bacteria to produce human proteins. Their first product was human insulin produced by genetically engineered Escherichia coli. A variety of other human hormones, blood proteins, and immune modulators are now produced in a similar fashion, in addition to...
Structure and Function
The RNA catalysts called ribozymes are found in the nucleus, mitochondria, and chloroplasts of eukaryotic organisms. Some viruses, including several bacterial viruses, also have ribozymes. The ribozymes discovered to date can be grouped into different chemical types, but in all cases the RNA is associated with metal ions, such as magnesium (Mg2+) or potassium (K+), that play important roles during the catalysis. Almost all ribozymes are involved in processing RNA. They act either as molecular...
Pregnancy and Infertility
There are many causes of infertility. Abnormal semen causes the infertility problems of about 30 percent of couples seeking treatment. Tubal disease and endometriosis in the female partner account for another 30 percent. A female partner's failure to ovulate accounts for 15 percent, and the inability of sperm to penetrate the woman's cervical mucus accounts for another 10 percent. The final 15 percent of couples seeking treatment are infertile for reasons that cannot be diagnosed. Many couples...
Similarities and Differences between Monozygotic Twins
The fertilized egg cell that gives rise to MZ twins begins life with a single set of genes, and so we might predict that every cell that arises from it would be exactly identical. However, small differences between daughter cells may accumulate throughout embryonic development and later in life. The earliest difference may be in the mitochondria each inherits. Mitochondria are the cell's power plants and contain a small amount of DNA. Some of the hundreds of mitochondria in a cell may contain...
Donor Insemination and Egg Donation
Donor insemination is used when sperm are incapable of fertilizing the egg. Usually this occurs if the male produces very little or no sperm. Sometimes, donor sperm is used when the male partner is the carrier of a genetic disorder that could be transmitted to the baby. Sperm donors should be between ages eighteen and fifty-five, and all should be screened for genetic disorders, such as cystic fibrosis, and for various types of chromosomal abnormalities and infectious disease, including...
Gamete Intrafallopian Transfer
An alternative to IVF and intrauterine embryo transfer is gamete intrafal-lopian transfer (GIFT), introduced more than twenty years ago. In this procedure, the egg and sperm are collected as they would be for IVF procedures. However, instead of allowing fertilization to take place in a culture dish, the egg and sperm are transferred surgically into the woman's fallopian tube. This allows fertilization to occur in the fallopian tube, just as occurs in a natural pregnancy. The transfer can only...
History and Disease Description
In 1881 Warren Tay, a British ophthalmologist, observed a cherry red spot in the retina of a one-year-old child with mental and physical retardation. Later, in 1896 Bernard Sachs, an American neurologist, observed extreme swelling of neurons in autopsy tissue from affected children. He also noted that the disease seemed to run in families of Jewish origin. Both physicians were describing the same disease, but it was not until the 1930s that the material causing the cherry-red spot and neuronal...
Twin Studies to Investigate the Cause of Parkinsons Disease
An example of the use of investigations in twins to understand more about a disease is provided by recent work in Parkinson's disease. Parkinson's disease (PD) is a progressive neurodegenerative disease causing slowness, tremor, and problems with walking and balance. PD is rare before age fifty but becomes more common thereafter, with increasing age. The cause of PD has long been debated. Both genetic and environmental causes have been suggested, but neither has been definitively shown....
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Gametes reproductive cells, such as sperm or percent normal T-lymphocytes. Learning from these gene therapy experiences, French researchers modified the procedure. In 2000 they reported successful gene therapy for two infants with SCID-X1. The patients had left the hospital and its protective isolation after a three-month stay. Ten months after gene therapy, they remained healthy, with normal levels of B- and T-lymphocytes and natural killer cells. Thus SCID continues to define the current...
The Risks of IVF
In some women, the drugs used to promote superovulation may cause side effects, including mood swings. Some investigators have suggested that procedures used in assisted reproductive technology may not be safe because of the potential for increased ovarian hyperstimulation syndrome and bone loss from the hormone treatments. Ovarian hyperstimulation syndrome occurs at mild levels in 23 percent of women undergoing the treatments, at moderate levels in 3 percent, and at severe levels in 0.1...
In Vitro Fertilization and Surrogacy
In vitro fertilization, even with anonymously donated ovum or sperm, is usually accepted as enabling a couple to experience gestation and create a fam ily. However, the in vitro procedure typically creates more embryos than will be implanted. These excess embryos are usually frozen and may remain viable (able to develop normally) for several years. Is it ethical to create embryos that will never be developed Are the embryos of a couple joint property, which can be divided upon divorce, or...
Intrauterine Insemination
Intrauterine insemination is used when a couple's inability to conceive a child is caused by the sperm's inability to reach the egg. Sperm must move through the uterus and enter the fallopian tube before they can fertilize the egg. Anything that prevents the sperm from making this trip will block conception. Coital or ejaculatory disorders can limit the sperm's travels, sperm antibodies in the female reproductive tract can kill the sperm, and sperm may be unable to penetrate the cervical mucus....
In vitro Fertilization
When performed by an experienced practitioner and in an experienced clinic, IVF generally results in pregnancy rates of about 28 percent after one attempt and 51 percent after three. One study has reported the pregnancy rate after six attempts as being 56 percent. Another has reported it as being 66 percent. Generally, one attempt at IVF is made per menstrual cycle. The IVF process begins when couples are first screened. Clinicians first must rule out infertility in the male partner. If the...
Insights from Laboratory Observation
Although anatomically and genetically simple, C. elegans mimics the life cycle of humans. Starting from a fertilized egg, it undergoes a complex development that gives rise to excretory, reproductive, digestive, and neuromuscular organ systems. The cell lineages of each of the 959 adult somatic cells have been directly observed, as has the fact that an additional unique set of 131 cells die during development. These deaths would have gone unnoticed, except for their demise was observable under...
Noncoding Triplet Repeat Disorders
The noncoding triplet repeat diseases typically have large and variable repeat expansions that result in multiple tissue dysfunction or degeneration. The triplet repeat sequences vary in this subclass (CGG, GCC, GAA, CTG, and CAG). It is clear that the particular triplet sequence and its location with respect to a gene are important defining factors in dictating the unique mechanism of pathogenesis for each disease. The pathogenic mechanism also varies from disease to disease depending on the...
Entering the Profession
In addition, technical writing is a profession that pays well. According to a 2000 salary survey by the Society for Technical Communication, the average salary for a technical writer in the United States. is about 52,000. An entry-level technical writer makes about 37,000, which compares favorably with entry-level positions in other fields. The average salary for a seniorlevel technical writer with supervisory responsibilities is about 65,000. Salary level also depends on geographic location,...
Simple Counting Mechanism
For the first half of the twentieth century it was believed that cells cultured in laboratory glassware could replicate indefinitely if the correct nutrient media and other conditions of growth could be found. Repeated initial failure at culturing indefinitely replicating cells was followed by success in the late 1940s, when the immortal L929 cancer cell population was developed from mouse tissue. Later, other immortal cell populations were found, including the first human cell line, HeLa,...
Mammalian Mechanisms
A developing mammalian embryo's gender is determined by two sequential processes known as primary and secondary sex determination. Primary Sex Determination. Early in an embryo's development (four weeks after fertilization, in humans), two groups of cells become organized into the gonad rudiment that will eventually develop into either the ovaries or testicles. These gonads will eventually be the source of gametes in the adult. However, at this early stage they are unstructured organs that lack...
