{module Science Square (Issue 128)}

First miniature human heart printed

Noor N et al. 3D Printing of Personalized Thick and Perfusable Cardiac Patches and Hearts.  Advanced Science, April 2019.

In a major breakthrough, researchers have “printed” the world’s first 3D vascularized engineered heart using a patient’s own cells and biological materials. This could have huge repercussions for human health: the World Health Organization said that last year, ischemic heart disease and stroke were the world’s leading cause of death for both men and women. Heart transplantation is currently the only treatment available to patients with end-stage heart failure. Given the serious shortage of heart donors, scientists have been trying to develop new “3D organ printing” approaches to regenerate the diseased heart. Past studies were only able to print simple tissues without blood vessels. The new study showed for the first time that an entire heart with cells, blood vessels, ventricles, and chambers could be successfully engineered and printed. The researchers first took a biopsy of fatty tissue from patients and separated the cellular and a-cellular materials of the tissue. While the cells were reprogrammed to become pluripotent stem cells, the extracellular matrix – a 3D network of extracellular macromolecules such as collagen and glycoproteins – were processed into a personalized hydrogel that served as the printing “ink.” After being mixed with the hydrogel, the cells were then robustly differentiated to cardiac or endothelial cells to create patient-specific, immune-compatible cardiac patches with blood vessels and, subsequently, an entire heart. The heart was 3D-printed in about three hours and was too small for humans. It was the size of a rabbit’s heart (~ 2.5 centimeters). But it is completely biocompatible and, most importantly, matches the patient, which reduces the chances of organ rejection inside the body. A human-sized heart might take a whole day to print and would require billions of cells, compared to the millions used to print these mini-hearts. While it’s not clear if a printer can produce hearts that are equal or superior to human ones, perhaps by printing patches there will be a possibility to improve or take out diseased areas in the heart and replace them with something that works. Researchers hope that maybe in 10 years, there will be organ printers in the finest hospitals around the world, and these procedures will be conducted routinely.

Bacterial factories for spider silk

Zhang F et al. Synthetic Biology for Microbial Production of Protein-based Materials, the American Chemical Society (ACS) National Meeting & Exposition, Spring 2019.

Spider silk has always fascinated researchers due to its lightweight and superior strength and numerous applications in areas such as drug delivery, smart textiles, and artificial muscles. It is one of the strongest natural materials in the world. It is thinner than a human hair, but its strength is more than that of steel, pound for pound. Since farming spiders is incredibly inefficient, scientists have been trying for decades to find a way to mass produce the material from genetically modified bacteria, yeast, and even goat milk, but these efforts have always fallen short. The biggest challenge was that the genetic information for dragline silk is a long string of repeating DNA, and, in previously tested organisms, cellular machinery arbitrarily alters or chops up such DNA sequences. To circumvent this problem, researchers precisely separated the repeating DNA into bits and inserted each repeating piece separately into bacterial genome. These smaller DNA pieces produced small peptides that ended up combining in bacteria and formed a strand of silk. The researchers also added to the end of each strand a chemical tag that glued the individual fibers together. This method was able to produce 2 grams of spider silk for each liter of bacteria and the resulting material behaved exactly like dragline silk. Its tensile strength was measured at 1.03 gigapascals, about the same as for naturally produced dragline silk. The engineered silk’s toughness measured 114 megajoules per cubic meter, compared with around 100 megajoules for silk made by spiders. And the engineered silk strands could stretch 18 percent before breaking, the same as natural dragline silk. The new silk was developed in part with NASA funding for applications such as giving astronauts a means of producing tough materials while on Mars. But the substance could be used in designing stronger materials for robotic, medical, or textile applications.

Electricity from falling snow

Ahmet A et al. All printable snow-based triboelectric nanogenerator. Nano Energy, April 2019.

Researchers have designed a new device with which we can now obtain electricity from falling snow. This new energy conversion method could become a new source of electricity in the future, especially in remote areas, as it does not need batteries. Researchers called it a Snow-based TriboElectric NanoGenerator, or Snow TENG. It is inexpensive, small, thin, and flexible like a sheet of plastic. After starting a charge from static electricity, energy is generated from the exchange of electrons. Snow is already positively charged by giving up its electrons, while silicone, a rubber-like material which consists of silicon atoms and oxygen atoms, is combined with carbon, hydrogen, and other elements to be negatively charged. When the positive-charged snow falls onto the surface of the silicone, the charges interact, and the Snow TENG captures the charge, which allows it to turn snowfall into electricity. 30% of Earth’s surface is covered by snow each winter, which is also the time when solar panels, one of the most reliable renewable sources of energy, aren’t very effective. Snow accumulation reduces the amount of sunlight that reaches the solar array, which makes them unable to operate. Snow TENG could be integrated into solar panels and provide a continuous power supply, even at a time when it’s snowing. Researchers used 3D printing to design the small device. It consists of a layer of silicone and an electrode which can capture the electric charge. Given that silicone is widely used in the industry, this method could dramatically reduce the global costs of producing electricity.

Agrochemical control of plant water use via engineered abscisic acid receptors
Park et al. Nature, February 2015.

A recent breakthrough study reported that scientists successfully engineered drought-tolerant plants by adding a new piece of DNA to their genomes. Crops and many types of plants are increasingly challenged by hostile environmental conditions such as globally warming temperatures and diminishing water sources. Plants have very small openings called “stomata” that let carbon dioxide in and oxygen out. Each stoma is surrounded by two guard cells that control opening and closing using osmotic pressure. During daytime, the stomata lets plants allow carbon dioxide in and oxygen out. Since the air around the leaves is often drier than inside, water molecules also move out through the stomata – a process called transpiration. Under the stress of drought, plants produce a hormone called abscisic acid (ABA). When ABA is released, it makes guard cells close the stomata and in turn keeps the plant from losing the water. Scientists previously thought that if they could spray ABA on a whole field, plants would survive a drought. However, since ABA is very expensive and highly sensitive to light, this strategy never became an option. Then, scientists decided to take the commonly used fungicide mandipropamid and genetically engineered the plants to respond to mandipropamid as if it were ABA. By adding a new piece of DNA into genomes, plants ended up having slightly different ABA receptors, which can be efficiently activated by mandipropamid.  Researchers tried this approach on two different plants: tomatoes and Arabidopsis. When mandipropamid was sprayed, genetically engineered plants stopped transpiration, and hence were able to survive for 12 days without water. The next challenge is to test this strategy in real world crops. This approach potentially opens new avenues for crop improvement that could highly benefit a growing world population.

3D Vaccines to Cure the Cancer

Injectable, spontaneously assembling, inorganic scaffolds modulate immune cells in vivo and increase vaccine efficacy
Kim J et al. Nature Biotechnology, December 2014.

Cancer is a devastating disease.  The World Health Organization (WHO) predicts that global cancer incidence rates will grow by nearly 60% to 22 million cases per year over the next two decades. The effective cure for cancer has not been developed yet, mostly due to its ability to escape the body’s immune system. Unlike infectious reagents like bacteria and viruses, cancer cells are actually our own cells that are broken and misplaced; they cause trouble as they grow. Scientists have been trying hard to develop vaccines that activate the immune system to recognize tumor cells as foreign and attack them. In a recent study, scientists reported that they designed a “3D vaccine” to effectively provoke the immune system to fight cancer. The 3D vaccine is composed of many microsized, porous silica rods submersed in liquid, where any combination of tumor antigens and immune-stimulating reagents can be loaded into.  Once the 3D vaccine is injected under the skin, it forms into a dime-sized scaffold that creates an “infection-mimicking microenvironment.” The scaffold then attracts the dendritic cells that patrol the body for harmful pathogens. When the scaffold was tested in mice, it showed over a 90% survival rate in animals that would normally die from lymphoma within 25 days. Further analyses in mice showed that the 3D vaccine can recruit, house, and manipulate immune cells to initiate a powerful immune response against cancer. As much as the discovery is promising, one should keep in mind that much more evidence will be required to establish 3D vaccines as a feasible way of combating human cancer.

Smoking Shrinks the Brain

Cigarette smoking and thinning of the brain’s cortex
Karama S et al. Molecular Psychiatry, February 2015.

Smoking is regarded as the single most preventable cause of disease, disability, and death. Past studies strongly linked smoking to cancer and lung diseases. A recent study now shows that smokers have a thinner brain cortex than non-smokers. The cortex is the outer brain layer in which critical cognitive functions such as memory, language, and perception take place. It is well known that the cortex becomes thinner with normal aging and cortical thinning is associated with cognitive decline and dementia. The study found that smoking accelerates this thinning process. Researchers analyzed brain MRI scans of 244 males and 260 females with an average age of 73, around half of whom were former or current smokers. Participants who had given up smoking for the longest time had a thicker cortex compared with those who had given up recently. Researchers cautiously suggest that the cortex might regain some thickness once smokers quit but the recovery is very slow and incomplete. For example, heavy smokers who had quit more than 25 years before still had a thinner cortex.

In general, the most common approach in tissue engineering is to develop tools as needed. Physicians treat patients and define the requirements for a better cure. Then, biologists study the targeted problem and learn what the mechanism is that caused the failure. Later, chemists and materials scientists manufacture the tools needed to treat the problem. Finally, the tools are delivered to doctors to treat the patients. Thus, tissue engineering requires a good understanding of how body parts work and come into existence, and this involves precise and sensitive application. Precise, aware and regular study of the interactions involved in tissues and organs must be practiced by the researchers who are interested in developing techniques for the manufacture of potential body parts. One of the first scientific approaches used for tissue engineering is to simply inject the body with molecules, such as growth factors, which are known to promote organ formation.

The growth factors are naturally occurring proteins which are assigned for cell proliferation and differentiation. Different parts of the body require different types of growth factors to signal to the cells to multiply or to replace the cells which have died or have been damaged. For example, it has been discovered that bone morphogenic proteins are responsible for the beginning of bone cell reproduction. For someone with a fractured bone that can not heal on its own within a reasonable period of time, the injection of bone growth factors to the site can direct the body to where bone cells are needed to be produced to repair the fracture.

In more severe conditions, the body may not receive the signal only with a simple injection of the growth factors. In this case, there is a need for more intricate treatment. Another way to treat organ malfunction starts with the harvesting of cells from the patient. The harvested cells can be multiplied in an artificial scaffold to eventually be implanted into the wound site. Because cells inhabit a different world than we do, we need a way to speak their language. The artificial scaffold should provide everything a cell needs and be able to direct the targeted cells toward the desired purpose. Basic knowledge gained from biology can help us to design potential artificial environments for cells.

A critical challenge in tissue engineering is how to design and make the artificial scaffolds. The cells must be fed through the blood vessel and are grown in the scaffold by the body; the scaffold should be able to communicate with the cells and finally the scaffold should disappear when its mission has been completed. The best example of a perfect scaffold is the natural environment of the cells, the extracellular matrix (ECM). The ECM provides support and anchorage for the cells and regulates communication between cells. There are various biological signals found in the ECM that help cell survival. For example, proteins called collagens provide mechanical support for cells through adhesive proteins in the ECM and the handles on the cell surface, known as integrins. Cell adhesion is crucial for cell survival and proliferation. Growth factors are also found in the ECM for cell organization. Some growth factors promote blood vessel formation, which can provide nutrients for cells. Therefore, a simple artificial environment should include various biological signals found in the ECM.

Currently, there are natural and synthetic scaffolds that are being used to generate the optimal environment for cells. Natural polymers such as collagen, chitosan or glycosaminoglycans, and synthetic polymers, including polylactic acid, polyglycolic acid, polycaprolactone or self-assembled nanofibers, are some of the materials used or considered for scaffold production. Natural polymers can be obtained easily, however biological contamination is a concern since they are produced using components from animals or microorganisms. Synthetic polymers can usually avoid the problem of contamination. Sometimes the ability to process the polymers can be problematic. Researchers have developed self-assembled nanofibers to overcome the problems that arise with synthetic and natural polymers. These nanofibers are composed of small molecules which are programmed to come together under control and to form larger structures. The nanofibers in the solution can form a three-dimensional network and convert into a self-supporting gel which can encapsulate cells as an artificial scaffold. In general, small bioactive molecules can be conjugated to the self-assembled molecules or can be encapsulated in situ in the 3-D network of fibers.

One of the recent uses of tissue engineering is to replace tissue that has been damaged by cancer. Cancer surgery is one of the most challenging types of surgery in that the defective tissue must be reconstructed afterwards. Improvement in surgical technology gives the chance of transferring a tissue from different sites of the body but unfortunately most of the time it is not the same tissue, and does not have the same texture or function. Reconstructing a resected tongue or the feeding tube is possible with the use of skin from the leg or forearm. But this skin does not provide the normal mucosal function, so it does not enable taste or sense to be perceived in the same way nor does it produce mucus in the same way. Together with advances in tissue engineering surgeons have started using the tissue-engineered mucosa of patients to reconstruct the mouth and feeding passage defects, instead of using the skin from chest, leg or forearm skin. These clinical applications of tissue engineering are in their very early stages, but it would not be surprising if we were able to reconstruct a lost organ from a similar one in the future. It would be exciting to be able to replace the tongue of a tongue cancer patient with a brand new tongue grown from his/her own tissues produced in a laboratory. Tasting the same…sensing the same…moving and even articulating the same…instead of having a piece of meat from another part of the body…

Innovative and imaginative work which has been inspired by natural materials demonstrates how the treatment of organ malfunctions is feasible. Efforts in biotechnology to develop tissue-engineered products will benefit many people who are searching for a healthier life. Potentially, in the near future, tissue-engineered products will be more widely used to treat bone fractures, serious skin burns, spinal cord injuries, diabetes, and heart diseases. Before implanting the tissue-engineered products, it is vital that there be extensive testing of the materials to be used. Toxicology and efficacy studies should be performed on the materials to prevent damage to the original healthy cells, and the new cells and regenerated tissue must be compared to original healthy cells and tissue.

Mustafa Guler has a PhD in chemistry. He is currently a research associate at Northwestern University, Chicago, IL. Joseph Coreman is a medical doctor at the Ohio State University Medical College, Columbus, OH.

References

• Khariwala SS, Vivek PP, Lorenz RR, Esclamado RM, Wood B, Strome M, Alam DS. Swallowing outcomes after microvascular head and neck reconstruction: a prospective review of 191 cases. Laryngoscope. 2007 Aug; 117(8):1359-63.
• Sauerbier S, Gutwald R, Wiedmann-Al-Ahmad M, Lauer G, Schmelzeisen R. Clinical application of tissue-engineered transplants. Part I: mucosa. Clin Oral Implants Res. 2006 Dec; 17(6):625-32.
• Hotta T, Yokoo S, Terashi H, Komori T. Clinical and histopathological analysis of healing process of intraoral reconstruction with ex vivo produced oral mucosa equivalent. Kobe J Med Sci. 2007;53(1-2):1-14.
• Ratner, Buddy D. “Biomaterials Science – An Introduction to Materials in Medicine” Elsevier, 2004.
• Lanza, Robert P., Robert S. Langer, William L. Chick, “Principles of Tissue Engineering”, Academic Press, 1997.
• Alberts, Bruce, Alexander Johnson, Julian Lewis, Martin Raff, Keith Roberts, Peter Walter, “Molecular Biology of the Cell” Garland Science, 2002.

Genetic engineering is one of the fastest developing fields of science. It continues to impact our lives in many ways: the Green Revolution, the quest for perfect animal stock, disease treatment, or human reproduction. But success also has brought concerns. Plants have become insect resistant and also more toxic. Genetically engineered cattle produce more milk but have mutated and overgrown. When scientists opened the window for asexual human reproduction, life became a commodity that could be produced in a culture dish.

And it all started when a monk experimented with some sweet peas…

From Mendel to Dolly

Modern genetic engineering dates back to 1865, when the Austrian monk Gregor Mendel performed a series of experiments with sweet pea plants. These experiments led to changes in the plants’ genetic construction. Genetic engineering, also known as bioengineering or recombinant DNA technology, is a general term referring to any alteration of an organism’s genes in order to make them produce new substances or perform new functions.(1) During the following years, these little experiments developed into a new field. The genes of plants and small-sized organisms were altered through crossing, but other than that research was limited.

In the 1930s, industrial corporations like America’s Rockefeller Foundation or, 20 years later, Germany’s Volkswagen Group (VW), discovered a different approach to raise economic efficiency. At the same time, motives of social control and surveillance directed the Rockefeller Foundation’s interest in the human body to the individual and the collective levels.(2) The Rockefeller Foundation outlined its rationale for supporting genetic research as follows: For the last 100 years physics and chemistry have reigned supreme, and the question of human behavior had been neglected. The new goal was to accomplish social control through understanding and knowledge of the very basic elements of the human body.(3) With the promise of benefit for their own corporations, they started sponsoring this new subfield of biology. The National Institutes of Health, private corporations, institutes, and universities established research laboratories. The idea was that if more actors and institutions shared and exchanged knowledge, the more molecular biology’s narration of life would be consolidated, disseminated, and legitimized.(4) 

Soon discoveries were reported from the science frontier. In 1953, M. Wilkins, F. Crick, and J. Watson discovered DNA’s double helix model while working at the University of Cambridge in England. In 1962, they received the Nobel Prize for their discovery. In 1968 Nirenberg, Khorana and Holley received a Nobel Prize for their interpretation of the genetic code and its function in protein synthesis.(5) 

The first frogs were cloned in 1970. In other words, an artificial copy of their embryo was produced. Soon this fast developing field of biology turned into a new industrial sphere. In 1980, industrial biotechnology emerged after the Supreme Court case of Diamond vs. Chakrabarty. In this case, Chakrabarty engineered and wanted to patent a certain kind of organism. After his request was denied, he went to court and received a favorable ruling. This decision led to the establishment of copyrights for living organisms, which ultimately industrialized the field. Producing and patenting new organisms were two crucial factors in the biotech industry’s development. Consider Steen Willadsen, who cloned the first sheep in 1984 from an embryo.(6) One year later, he mass-produced prize cattle embryos for Grenada Genetics in order to raise a perfect stock.(7) However, that project soon was stopped because of the cloned cattle’s high and death rates and abnormal behavior.

Since the biologic make-up of many mammals had been unveiled, scientists now had a new goal: exploring the human being. Therefore the U.S. Department of Energy launched the human genome project. Soon biotech giants like Celera and many private institutions got into the race. Their goal was to map the entire human genome in order to identify and eliminate disease-causing genes. This project raised certain concerns about what would be done with an individual’s DNA information, who could access it (e.g., insurance companies and employers), and genetic discrimination.

The first human embryos were cloned in 1993. Four years, later the whole world got to meet Dolly, the first sheep cloned from an adult cell. This was an important development, for it opened the door to asexual reproduction. But despite the great enthusiasm with this achievement, some people started wondering about possible dangers. Finally in June 2000, Bill Clinton announced the completion of the human genone project.

Applications and drawbacks

Genetic engineering has penetrated into various parts of our life. Agriculture has seen a Green Revolution. Herbicide-resistant plants were engineered to have built-in pesticide resistance and to convert nitrogen directly from the soil. By April 2002, the approximately 50,000 rice genes had been discovered. Scientists already are working on ways to alter rice, the main food of the world’s population, so that it will be more nutritious and resistant. Insects are being engineered to attack crop predators. Researchers are growing agricultural products in the laboratory using genetically altered bacteria. A major commercial role for genetically engineered plants as chemical factories is also envisioned, such as organic plastics.

Some drawbacks of this revolution are increased toxins and diseases, which are causing the resulting organisms to become resistant to antibiotics. Increased toxins in plants were designed to make insect-resistant plants. Nuclear physicist Dr. John Hagerlin testified in Washington, DC, at the Food and Drug Administration’s (FDA) public hearing that increased toxins trigger unanticipated allergic reactions. The resulting gene pollution threatens the environment, for it breaks down genetic barriers put in place by Nature.(8)

Industrial mistakes in production or insufficient research in engineered food ingredients also can cause serious problems. The Tryptophan food supplement, an amino acid marketed as a natural tranquilizer and sleeping pill, was mass-produced from genetically altered bacteria. It killed 37 persons and permanently disabled over 1,500 others with an incurable nervous system condition known as eosinophilia myalgia syndrome (EMS).(9) When these technologies were applied to livestock, farmers first were pleased that the engineered cattle produced more milk, grew faster, and yielded more meat. However, cases of mutation and rampant overgrowth have caused scientists to reevaluate the effectiveness of these procedures.

Another important issue is inserting human genes in animals. What percent of human genes does an organism have to contain before it is considered human? If humans have a special ethical status, does the presence of human genes in an organism change its ethical status? What about a genetically engineered mouse that produces a human sperm that is then used to conceive a human child?(10) Or a pig that contains human genes in order to grow organs that can be transplanted to humans?(11)

It is shocking that the FDA issued guidelines in September 1996 that allow animal-to-human transplants, even though a group of 44 top virologists, primate researchers, and AIDS specialists, opposed it. They attacked the FDA guidelines, saying that based on knowledge of past cross-species transmissions (e.g., AIDS, Herpes B, Ebola, and other viruses), using animals was not adequately justified for use in a handful of patients. Vast numbers of people could be injured or even killed if a new infectious agent were to be transmitted.(12) The FDA puts the responsibility for health and safety on local hospitals and medical review boards.

Recombinant DNA technology also has been applied directly to the human body. After mapping the entire genome, scientists discovered some disease-causing genes. They are now working to isolate those genes and develop molecular-level treatments. Although curing Alzheimers, nuscular dystrophy, and many other inherited diseases would make patients happy, unexpected results may occur. When applying gene therapy, a one-to-one correspondence between the gene and its function is assumed. Since genes interact in a horizontal manner, as scientists have shown, introducing a new gene could have unforeseen effects.(13)

Genetic manipulation in human beings always encompasses the possibility of designer genes that manipulate a child’s appearance, IQ, or behavior. According to a March of Dimes survey, 40 percent of Americans would use gene therapy to enhance their children’s looks or intelligence. Even picking your child’s gender has become a question of money. A Fairfax, Virginia-based genetics and in-vitro fertilization institute offers family balancing for approximately $3,000. Known as microsort, the male sperm is separated from the female one. In 2001, the institute treated around 60 couples a month and planned to double its production. Fortune Magazine calculated that the microsort market could be worth $200 million.(14)

There is also talk that people could be exploited as producers of certain substances. For example, a biotech corporation applied to the European Patent Office for a patent on a so-called pharm woman. The idea was to genetically alter women so that their breast milk would contain specialized pharmaceuticals.(15)

Related debates

There are many other largely debated topics in this field, but the most controversial one of all is human cloning life. This is divided into therapeutic cloning and reproductive cloning.

In therapeutic cloning, scientists produce embryos in culture dishes to harvest their stem cells. These then are used in further research, the long-term goal of which is to produce replacement organisms. Stem cells are undifferentiated and primitive cells that can be found in embryos as well as in an adult body.(16) Researchers intend to isolate stem cells so they can serve as a starter stock for growing replacement nerve, muscle and other tissue that might one day be used to treat patients with various diseases.(17) Even though this procedure sounds very promising, we should not overlook the fact that embryos are mass-produced to harvest stem cells. Once these have been isolated, the embryo becomes useless and disposable. The ethics of this procedure are questionable, since stem cells also could be harvested from an adult human body.

Reproductive cloning intends to implant such a cloned embryo into a woman’s uterus. Although this procedure is not safe for either the mother or the child, Severino Antinori announced that he and his team will soon produce the first cloned child. The Whitehead Institute of Biomedical Research revealed that cloned mice possess subtle genetic defects that could eventually wreak havoc on the animals system. This means that even though a cloned child might appear completely normal at birth, it has to expect serious health problems later in life.(18)

There also are potential psychological risks for a cloned child. Dr. Thomas Murray worries about the child’s self-identity problem once he/she finds out that he/she is a clone and how he/she was conceived.(19) George Johnson, a professor at Washington University, opposes cloning because genetic variation is the chief defense our species has against an uncertain future. If we strip ourselves of it even partially, it is to endanger our species.

Conclusion

Recombinant DNA technology faces our society with problems unique not only in the history of science but also life on the Earth as well as legal approaches towards them. It places in human hands the capacity to redesign living organisms. It presents probably the largest ethical problem science has ever had to face. Our morality up to now has been to go ahead without restrictions to learn what we can about nature. Reconstructing nature was not part of the bargain. Going ahead in this direction may not be only unwise but also dangerous. Potentially it could breed new animal and plant diseases, new sources of cancer and novel epidemics.(20)

Since creation is in a perfect balance, interventions might have unforeseen effects. A book must be written by an author, a picture must be painted by an artist, and a poem must be written by a poet. Each piece of art has an artist who has an encompassing knowledge of his/her creation. If we do not understand that nature is a perfectly composed book, our writings will be no more than scribbles between the lines.

Footnotes

1. http://209.52.56.28/lexicon/g.html.
2. Lily E. Kay, The Molecular Vision of Life: Caltech, the Rockefeller Foundation, and the Rise of the New Biology (Oxford: Oxford University Press, 1993), 26.
3. Herbert Gottweiss, Governing Molecules: The Discursive Politics of Genetic Engineering in Europe and the US (Cambridge MA: The MIT Press, 1998), 42.
4. Ibid., 46.
5. www.nobel.se/medicine/laureates/1968/index.html.
6. www.dartmouth.edu/artsci/courses/coco25/Cloning/The_History_of_Cloning.html.
7. http://library.thinkquest.org/24355/data/details/1985.html?tqskip1=1&tqtime=0508.
8. www.netlink.de/gen/hagelin.html.
9. www.psrast.org/jftrypt.htm.
10. Surrogate Fathers, New Scientist (31 Jan. 1998).
11. Robert Pool, Saviors, Discover, (May 1998): 53-57. (special issue.)
12. IP/BiodivNews, 1-24-97 or http://online.sfsu.edu/~rone/GE%20Essays/Redigning.htm#40.
13. Horizontal gene transfer refers to the transfer of genes to unrelated species by infection through viruses, through pieces of genetic material, DNA by being taken up into cells from the environment, or by unusual mating taking place between unrelated species. (Mae-Wan Ho, Genetic Engineering: Dream or Nightmare, 2d rev. [Continuum Pub Group: 2000),
14. The Economist (14 Apr. 2001): 22.
15. Andrew Kimbrell, The Human Body Shop: The Engineering and Marketing of Life (New York: Harper Collins, 1994), 191.
16. Popular Science (Jan. 2002): 58.
17. Scientific American (Jan. 2002): 45.
18. Gunjan Sinha, Popular Science (Jan. 2002)
19. Thomas Murray, Talk of the Nation broadcast, 24 Feb. 1997.
20. George Wald, The Case Against Genetic Engineering, in The Recombinant DNA Debate, eds. David A. Jackson and Stephen P. Stich (Prentice Hall College Div: 1979), 127-28.

Plant breeding has several other serious limitations for use as a tool to increase disease resistance. There are only a limited number of plant species which are able to cross-fertilize, thus restricting the transfer of potentially useful traits. Moreover, having found useful traits, it is impossible to prevent the co-transfer of undesirable ones, which can take many years to breed out again by back-crossing.

How can genetic engineering be of use in the quest for new answers to the problems of providing plants with the ability to resist disease? The aim of crop plant genetic engineering is to insert a gene (or genes) which improve an existing plant variety whilst retaining the desirable genetic make up of the original plant.

The main tool at the disposal of the scientist is the use of nature’s own genetic engineer, Agro-bacterium tumefaciens. The manipulation of this bacterium’s natural functions has allowed the biologist to transfer many foreign genes into plants. The bacterium is soil-borne and infects plants at the crown, usually through a wound site, causing cancerous growths of proliferating plant cells known as crown gall tumors. This disease in itself is ergonomically important and effects most dicotyledonous plants causing millions of dollars’ worth of damage to plants. In the 1940s, from experimental observations, it was concluded that a factor is transmitted from the invading bacteria to the host plant cell. Further studies demonstrated that the disease is actually the direct result of the transfer of a particular DNA fragment (genes) from the bacterium to the plant cell. In addition to its chromosomal DNA, Agro-bacterium contains a much smaller circular DNA molecule called a Ti (tumor-inducing) plasmodia, of which a small piece, called the T-DNA (Transferred-DNA), is the factor transferred into plant cells (see Figure 1). The T-DNA becomes stably integrated into the plant’s chromosomes, from where it is able to perturb the natural functions of the plant. The T-DNA encodes genes, which, when expressed, bring about the production of new enzymes that are able to alter the hormone balance within the infected cell. This brings about de-differentiation and cell division, leading to proliferation of cells and the formation of tumors. This appears to be of little benefit to the bacterium. However, other genes are also present in the T-DNA which, when expressed, are able to synthesize novel compounds from naturally occurring plant precursors. These novel compounds cannot be metabolized by the plant but are a good source of nutrients for the bacterium.

Mutation analysis of the T-DNA revealed two regions, the left and right borders, which were essential for integration into the chromosome. It was also found that any piece of DNA inserted between these borders was stably inserted into the host chromosome on transformation. Deletion of the genes for tumor formation (Disarmed Ti-Plasmid) were found to have no effect on the transfer efficiency from bacterium to plants. Availability of disarmed Ti-plasmids, tissue culture methods for the regeneration of whole fertile plants from single cells, and marker genes (such as antibiotic resistance) for the selection of transformed cells, have allowed for the production of a whole new range of plants containing foreign genes. Several genes responsible for pathogen and herbicide resistance proteins have been isolated from the bacteria and viruses. These genes have then been inserted into the T-DNA region of Agro-bacterium and introduced into plants, giving rise to insect, virus or herbicide resistant plants.

By using Agro-bacterium as a plant genetic engineer, many crop plants such as the tomato, potato and cucumber have now been engineered for virus resistance. Field tests showed that these genetically modified plants appeared to be highly resistant to viral infections. Similarly genetically-engineered cotton plants have proved to be resistant to insect attack and many herbicides (weed killers).

Another powerful new genetic engineering technique is ‘antigens’ technology, whereby specific gene transcripts are prevented from being translated into proteins. By using antigens technology, it has been possible to produce genetically engineered tomato plants that have a much increased shelf-life. Although many aspects of gene transfer from Agro-bacterium to plants are not fully understood, the use of Agro-bacterium for gene transfer will continue to increase; and it is likely that genetically engineered crops carrying traits for resistance to herbicides, insects and viral diseases will soon reach the market-place.