Cohen, Stanley N. (1935- )

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Cohen, Stanley N. (1935- )

American geneticist

Modern biology, biochemistry , and genetics were fundamentally changed in 1973 when Stanley N. Cohen, Herbert W. Boyer , Annie C. Y. Chang, and Robert B. Helling developed a technique for transferring DNA , the molecular basis of heredity, between unrelated species. Not only was DNA propagation made possible among different bacterial species, but successful gene insertion from animal cells into bacterial cells was also accomplished. Their discovery, called recombinant DNA or genetic engineering, introduced the world to the age of modern biotechnology .

As with any revolutionary discovery, the benefits of this new technology were both immediate and projected. Immediate gains were made in the advancement of fundamental biology by increasing scientists' knowledge of gene structure and function. This knowledge promised new ways to overcome disease, increase food production, and preserve renewable resources. For example, the use of recombinant DNA methodology to overcome antibiotic resistance on the part of bacteria anticipated the development of better vaccines. A new source for producing insulin and other life-sustaining drugs had the potential to be realized. And, by creating new, nitrogen-fixing organisms, it was thought that food production could be increased, and the use of expensive, environmentally harmful nitrogen fertilizers eliminated. Genetic engineering also offered the promise of nonpolluting energy sources, such as hydrogen-producing algae. In the decades following the discovery of the means for propagating DNA, many assumptions regarding the benefits of genetic engineering have proved to be viable, and the inventions and technology that were by-products of genetic engineering research became marketable commodities, propelling biotechnology into a dynamic new industry.

Stanley N. Cohen was born in Perth Amboy, New Jersey, to Bernard and Ida Stolz Cohen. He received his undergraduate education at Rutgers University, and his M.D. degree from the University of Pennsylvania in 1960. Then followed medical positions at Mt. Sinai Hospital in New York City, University Hospital in Ann Arbor, Michigan, the National Institute for Arthritis and Metabolic Diseases in Bethesda, Maryland, and Duke University Hospital in Durham, North Carolina. Cohen completed postdoctoral research in 1967 at the Albert Einstein College of Medicine in the Bronx, New York. He joined the faculty at Stanford University in 1968, was appointed professor of medicine in 1975, professor of genetics in 1977, and became Kwoh-Ting Li professor of genetics in 1993.

At Stanford Cohen began the study of plasmids bits of DNA that exist apart from the genetic information-carrying chromosomes to determine the structure and function of plasmid genes. Unlike species ordinarily do not exchange genetic information. But Cohen found that the independent plasmids had the ability to transfer DNA to a related-species cell, though the phenomenon was not a commonplace occurrence. In 1973 Cohen and his colleagues successfully achieved a DNA transfer between two different sources. These functional molecules were made by joining two different plasmid segments taken from Escherichia coli , a bacteria found in the colon, and inserting the combined plasmid DNA back into E. coli cells. They found that the DNA would replicate itself and express the genetic information contained in each original plasmid segment. Next, the group tried this experiment with an unrelated bacteria, Staphylococcus. This, too, showed that the original Staphylococcus plasmid genes would transfer their biological properties into the E. coli host. With this experiment, the DNA barrier between species was broken. The second attempt at DNA replication between unlike species was that of animal to bacteria. This was successfully undertaken with the insertion into E. coli of genes taken from a frog. This experiment had great significance for human application; bacteria containing human genetic information could now be used to create the body's own means for fighting disease and birth disorders. The biological cloning methods used by Cohen and other scientists came to be popularly known as genetic engineering. The cloning process consisted of four steps: separating and joining DNA molecules acquired from unlike species; using a gene carrier that could replicate itself, as well as the unlike DNA segment joined to it; introducing the combined DNA molecule into another bacterial host; and selecting out the clone that carries the combined DNA.

DNA research not only added to the store of scientific knowledge about how genes function, but also had practical applications for medicine, agriculture, and industry. By 1974, there was already speculation in the media about the benefits that could accrue from gene transplant techniques. The creation of bacteria "factories" that could turn out large amounts of life-saving medicines was just one possibility. In fact, insulin made from bacteria was just seven years from becoming a reality. Still in the future at that time, but proved possible within two decades, were supermarket tomatoes hardy enough to survive cross-country trucking that taste as good as those grown in one's own garden. Using DNA technology, other plants were also bred for disease and pollution resistance. Scientists also projected that nitrogen-fixing microbes, such as those that appear in the soil near the roots of soybeans and other protein-rich plants, could be duplicated and introduced into corn and wheat fields to reduce the need for petroleum-based nitrogen fertilizer. Cohen himself said, in an article written for the July 1975 issue of Scientific American: "Gene manipulation opens the prospect of constructing bacterial cells, which can be grown easily and inexpensively, that will synthesize a variety of biologically produced substances such as antibiotics and hormones, or enzymes that can convert sunlight directly into food substances or usable energy."

When news of this remarkable research became widespread throughout the general population during the 1970s and 1980s, questions were raised about the dangers that might be inherent in genetic engineering technology. Some people were concerned that the potential existed for organisms altered by recombinant DNA to become hazardous and uncontrollable. Although safety guidelines had long been in place to protect both scientists and the public from diseasecausing bacteria, toxic chemicals, and radioactive substances, genetic engineering seemed, to those outside the laboratory, to require measures much more restrictive. Even though, as responsible scientists, Cohen and others who were directly involved with DNA research had already placed limitations on the types of DNA experiments that could be performed, the National Academy of Sciences established a group to study these concerns and decide what restrictions should be imposed. In 1975, an international conference was held on this complicated issue, which was attended by scientists, lawyers, legislators, and journalists from seventeen countries. Throughout this period, Cohen spent much time speaking to the public and testifying to government agencies regarding DNA technology, attempting to ease concerns regarding DNA experimentation.

Cohen contended that public outcry over the safety of DNA experiments resulted in an overly cautious approach that slowed the progress of DNA research and reinforced the public's belief that real, not conjectural, hazards existed in the field of biotechnology. In an article on this subject published in 1977 for Science he pointed out that during the initial recombinant DNA experiments, billions of bacteria played host to DNA molecules from many sources; these DNA molecules were grown and propagated "without hazardous consequences so far as I am aware. And the majority of these experiments were carried out prior to the strict containment procedures specified in the current federal guidelines."

The controversy over the safety of DNA technology absorbed much of Cohen's time and threatened to obscure the importance of other plasmid research with which he was involved during those years. For instance, his work with bacterial transposons , the "jumping genes" that carry antibiotic resistance, has yielded valuable information about how this process functions. He also developed a method of using "reporter genes" to study the behavior of genes in bacteria and eukaryotic cells. In addition, he has searched for the mechanism that triggers plasmid inheritance and evolution . Increased knowledge in this area offers the medical community more effective tools for fighting antibiotic resistance and better understanding of genetic controls.

Cohen has made the study of plasmid biology his life's work. An introspective, modest man, he is most at home in the laboratory and the classroom. He has been at Stanford University for more than twenty-five years, serving as chair of the Department of Genetics from 1978 to 1986. He is the author of more than two hundred papers, and has received many awards for his scientific contributions, among them the Albert Lasker Basic Medical Research Award in 1980, the Wolf Prize in Medicine in 1981, both the National Medal of Science and the LVMH Prize of the Institut de la Vie in 1988, the National Medal of Technology in 1989, the American Chemical Society Award in 1992, and the Helmut Horten Research Award in 1993. Cohen has held memberships in numerous professional societies, including the National Academy of Sciences (chairing the genetics section from 1988 to 1991), the Institute of Medicine of the National Academy, and the Genetics Society of America. In addition, he served on the board of the Journal of Bacteriology in the 1970s, and was associate editor of Plasmid from 1977 to 1986. Since 1977, he has been a member of the Committee on Genetic Experimentation for the International Council of Scientific Unions. Married in 1961 to Joanna Lucy Wolter, and the father of two children, Cohen lives mostly near Stanford University in a small, rural community. Free time away from his laboratory and his students has been spent skiing, playing five-string banjo, and sailing his aptly named boat, Genesis.

See also Microbial genetics