Techniques and tools such as knockout mice, gene and protein expression studies, and protein tracking experiments, are mainstays of research about genetic manipulation. How do these techniques work?
Following the completion of the Human Genome Project we have a vast amount of data about the human genome— all 3.3 billion base pairs and 30,000 genes of it. However, while we know how many genes there are, relatively little is known about their functions. In fact, for more than half of the genes in the human genome, the function is unknown.
The following tools and techniques are a small sampling of the ways in which the function of genes—and the proteins they code for—can be discovered and examined.
Function Experiments
There are two main classes of functional experiments in research about genetic manipulation: those in which the function of a gene is removed, and those in which it is added.
- Function loss experiments typically involve what are called knockout mice. These are a strain of mice in which a specific gene has been knocked out so that it is no longer functional. By creating such a mouse, researchers can examine what happens to the animal when the gene of interest is non-functional, and the consequences of the lack of the protein for which the gene codes.
- Function gain experiments involve enhancing the function of a specific gene, typically so that it produces more of the protein it codes for. To do this, multiple copies of the gene are generally inserted into the experimental animal’s genome. These types of experiments allow researchers to examine the function of a given gene more closely.
Tracking Experiments
Where do proteins go once they are produced and correctly folded? Protein tracking experiments show researchers where in the body—in what organs or tissues—a given protein interacts to carry out its function. Depending on the experiment involved, it can also provide information about how the protein travels and in what fashion it interacts with other molecules.
Typically, these experiments involve the fusion of the gene of interest to a gene that produces a visual read-out which allows researchers to see where the protein is located. In the past, the most commonly used of these has been the gene for Green Fluorescent Protein, which was isolated from a species of jellyfish. However, recently new and more sophisticated techniques are being developed due to concerns over whether the addition of GFP has an effect on the function of the gene and protein being studied.
Expression Studies
Where are proteins produced? When and under what circumstances? Protein expression studies are another tool used to examine the expression of genes, and the creation of protein products.
In these types of experiments, a reporter gene (such as Green Fluorescent Protein) is used to track the time and place where the protein of interest is produced. For example, this means researchers can determine the conditions under which a given protein is produced, and examine the factors that cause expression or suppression of the gene that codes for the protein.