Genetically modified organisms (GMOs) are a controversial topic. Broadly speaking, they can be defined as “any organism whose genetic material has been altered using genetic engineering techniques”. In this case, “genetic material” refers to an organism’s DNA, which is the heritable blueprint of life. DNA has four “letters”: A, C, G, and T. Different combinations of these create “words” (called genes) which can be read by our cell’s machinery to build proteins. Proteins are the workhorse molecules of life, performing a diverse set of important tasks in the body, such as producing energy and providing structure to your cells.
The definition of GMO given above covers a range of different organisms modified in different ways for different purposes. Much of the controversy surrounding GMOs is related to genetically modified plants and animals intended for human consumption. One example is golden rice, a strain of rice that has had genes inserted into it that cause the rice grains to produce beta-carotene, a molecule that can be converted into vitamin A in the gut. This crop is designed for agricultural use in areas of the world where people do not obtain enough vitamin A from their diet. Children who do not get enough of this vitamin become blind, and are at a greater risk from infections.
However, there are other GMOs that are in widespread use in the field of medicine, where they have revolutionised the way we treat diseases and have saved many lives in the process. My aim in this blog post is to explain how GMOs make useful products for us, and highlight the diversity of organisms and applications encompassed by the broad term “GMO”.
GMOs are vital to our modern treatment of diabetes. Type I diabetes is a disease where a person’s own immune system destroys the cells in the pancreas which produce insulin, a protein that plays a vital role in the regulation of the body’s sugar metabolism (Figure 1). People who suffer from type I diabetes must regularly inject themselves with insulin (as often as 5 times per day), or risk harmful or even fatal drops in their blood sugar levels.
Historically, insulin for diabetics was obtained from the pancreases of pigs, as humans and pigs share many of the same fundamental proteins. However, this method for obtaining insulin was very inefficient, being expensive and producing only little insulin, in addition to being non-vegetarian! To solve this problem, in 1978 scientists inserted the gene that encodes for human insulin into the bacterium E. coli, creating a GMO to produce large quantities of insulin for those that need it.
Bacteria are small, single-celled organisms. Some can be rapidly and easily grown inside laboratories, making them the perfect organism to be a “production factory” for proteins of interest (Figure 2). Many bacteria have small circular pieces of DNA (called plasmids) in addition to their core DNA. We can design our own plasmids to contain the genes for the proteins we wish to make e.g. insulin. These plasmids can then be inserted into the bacteria, and at our command a molecular “switch” in the plasmid can be turned on—instructing the bacteria to produce large quantities of the protein. Once sufficient protein has been made, the bacteria are sacrificed, and the protein of interest is separated from the destroyed cell fragments. In the case of the modified E. coli, the resulting insulin is then provided for diabetics who need it to survive.
Genetic modification allows us to efficiently produce any protein from any organism in large quantities. Some widely used proteins that are produced using GMOs include:
Rennet, an essential protein used in cheesemaking, which would normally be obtained from the stomachs of calves.
Human growth hormone, an important growth-regulator that is given to people who cannot produce enough. Prior to genetic modification technology this protein was obtained from cadavers, which was an unsafe practice as prion diseases – such as Creutzfeldt–Jakob disease – could be spread from cadaver to patient.
Blood clotting factor VIII (FVIII), a protein that assists in blood clotting and is given to people who cannot make it themselves, for example those with the disease hemophilia A. Without FVIII, these people could die from a small cut. This protein was previously made by concentrating down large quantities of donor blood. But this process was wasteful, and potentially dangerous as blood borne infectious diseases could be spread this way.
In addition to producing proteins of great value to society, genetic modification has also revolutionised molecular biology and medical research. Scientists can now produce proteins they are interested in studying, e.g. a disease-causing protein from a bacterium, which they can then use in experiments to find treatments and develop vaccines.
GMOs have revolutionised medical and basic research, and have allowed us to provide safe and sufficient medicine for those that need it. Regardless of where you stand on the topic of other applications, such as genetically-modified foods, genetic modification technology has been a major benefit to society.