It involves the isolation, manipulation and reintroduction of DNA into cells, usually to produce a new protein function. The aim is to introduce new characteristics or traits that affect the normal physiology or morphology of the final organism. Engineering crop resistant to a herbicide or mass producing a specific protein or enzyme and common examples that have reached the market. The production of human insulin through the use of modified bacteria, the production of erythropoietin (EPO) in Chinese hamster ovary cells (CHO) are two examples products routinely used for medicinal uses. Model systems for studying human diseases, such as the OncoMouse (cancer mouse), are routinely designed to have a higher susceptibility for a disease. This is often achieved by introducing a segment of DNA with a defective gene that is thought to be associated with the disease in humans.
Since a protein is specified by a gene, future versions any protein can be modified by changing the DNA sequence of the gene that encodes for that protein. One way to do this is to isolate the piece of DNA containing the gene, precisely cut the gene out, and then recombine the gene of interest with other fragments of DNA. This recombination of specific DNA fragments is critical for genetic engineering and a key resource for this was the isolation of restriction endonucleases, which are able to cut DNA at specific sites. For this discovery, Daniel Nathans and Hamilton Smith received the 1978 Nobel Prize in physiology or medicine and together with ligase, which can bond specific fragments of DNA together, this formed the basis for all future recombinant DNA technology.
The first Genetically Engineered drug was human insulin approved by the USA's FDA in 1982. Another early application of GE was to create human growth hormone as replacement for a drug that was previously extracted from human cadavers. In 1986 the FDA approved the first genetically engineered vaccine for humans, for hepatitis B. Since these early uses of the technology in medicine, the use of GE has expanded to supply many drugs and vaccines.
One of the best known applications of genetic engineering is that of the creation of genetically modified organisms (GMOs).
DNA sequencing is a technique which is used to identify each base in DNA. Although the costs of DNA sequencing has dropped dramatically, the NIH estimates it costs at least $10 million to sequence 3 billion base pairs- the size of the whole human genome.
Genetic engineering and research
Although there has been a tremendous revolution in the biological sciences in the past twenty years, there is still a great deal that remains to be discovered. The completion of the sequencing of the human genome, as well as the genomes of most agriculturally and scientifically important plants and animals, has increased the possibilities of genetic research immeasurably. Expedient and inexpensive access to comprehensive genetic data has become a reality with billions of sequenced nucleotides already online and annotated. Now that the rapid sequencing of arbitrarily large genomes has become a simple, if not trivial affair, a much greater challenge will be elucidating function of the extraordinarily complex web of interacting proteins, dubbed the proteome, that constitutes and powers all living things. Genetic engineering has become the gold standard in protein research, and major research progress has been made using a wide variety of techniques, including:
- Loss of function, such as in a knockout experiment, in which an organism is engineered to lack the activity of one or more genes. This allows the experimenter to analyze the defects caused by this mutation, and can be considerably useful in unearthing the function of a gene. It is used especially frequently in developmental biology. A knockout experiment involves the creation and manipulation of a DNA construct in vitro, which, in a simple knockout, consists of a copy of the desired gene which has been slightly altered such as to cripple its function. The construct is then taken up by embryonic stem cells, where the engineered copy of the gene replaces the organism's own gene. These stem cells are injected into blastocysts, which are implanted into surrogate mothers. Another method, useful in organisms such as Drosophila (fruit fly), is to induce mutations in a large population and then screen the progeny for the desired mutation. A similar process can be used in both plants and prokaryotes.
- Gain of function experiments, the logical counterpart of knockouts. These are sometimes performed in conjunction with knockout experiments to more finely establish the function of the desired gene. The process is much the same as that in knockout engineering, except that the construct is designed to increase the function of the gene, usually by providing extra copies of the gene or inducing synthesis of the protein more frequently.
- 'Tracking' experiments, which seek to gain information about the localization and interaction of the desired protein. One way to do this is to replace the wild-type gene with a 'fusion' gene, which is a juxtaposition of the wild-type gene with a reporting element such as Green Fluorescent Protein (GFP) that will allow easy visualization of the products of the genetic modification. While this is a useful technique, the manipulation can destroy the function of the gene, creating secondary effects and possibly calling into question the results of the experiment. More sophisticated techniques are now in development that can track protein products without mitigating their function, such as the addition of small sequences which will serve as binding motifs to monoclonal antibodies.
- History of Genetic Engineering A Timeline of Significant Events in the History of Genetic Engineering.
- 2004 News Release: NHGRI Seeks Next Generation of Sequencing Technologies