Gene silencing is a technique that results in stopping the expression of a gene, effectively turning the gene off. This is a natural process in cells that is accomplished by epigenetic changes, changes to the genome that are not changes in the sequence; DNA-protein interactions; and RNA-DNA interactions. In order to understand why scientists would want to use gene silencing, the types of silencing need to be understood on some level.
Epigenetics is a new and emerging field of genetics attempting to understand this process. One natural process is DNA methylation. This is accomplished by enzymes that add a methyl group to CpG islands, patches of CG-rich regions in the genetic sequence. Histone modifications, the protein structures around which chromosomes are wound, are another epigenetic possibility.
DNA-protein interactions may include mutations in the DNA sequence that affect protein binding to the DNA. Methylation also may involve DNA-protein interactions by stalling transcription. Some proteins recognize short DNA sequences and bind to the DNA strand for transcription, if a particular allele is present it may cause an additional protein or alternative protein to bind that blocks transcription, thus silencing the gene. There are also silencer sequences that cause the machinery to stall and prevent gene expression.
RNA plays a role in gene silencing as short interfering sequences (si RNA) that bind the transcribed RNA and prevents expression by promoting the destruction of the mRNA before it can be translated into protein. This is a fairly new technique called RNAi , and it is being used more commonly in labs as the current decade progresses.
Scientists use gene silencing in an experimental context to determine the role a gene or mutation plays in the living organism. By silencing a gene in a cell culture or animal model, researchers can determine what processes are affected by the absence of the protein and in what way. This is a definitive method of determining the role of a gene in disease. If the lack of the gene product results in no disease, then the presence of the gene product (i.e. expression of the gene) plays a role in that disease. This indicates genes of interest for further study involving treating and curing disease. Also, in addition to unveiling more of the pieces in the genetic puzzle of chromosomes and nucleotides, studying gene silencing helps scientists understand the complex, natural processes of gene expression.
Medically, gene silencing is a method for developing new therapeutic approaches to diseases caused by excess gene expression. If doctors can silence the deranged gene, they can (theoretically) cure diseases like cancer. Interfering RNA is currently the subject of clinical trials for treating Huntington’s Disease, some types of cancer, growth deficiencies, and as an antiviral therapy for hepatitis, among others.