Biomedical researchers are turning to gene expression profiling to better understand the conditions under which certain genes are turned on or off — exploring the many variables that influence cellular function. Today, gene profiling studies are playing a valuable role in hypothesis generation and testing, in drug R&D as a method to pinpoint biomarkers, and even as a diagnostic tool in cancer treatment.
Let’s take a closer look at what gene expression profiling is and how it’s accomplished.
What is gene expression?
Inside a single cell, thousands of genes work to encode the proteins that determine how a particular cell operates. This information, stored inside our DNA, can be converted into instructions for making proteins or other molecules. In gene expression, DNA transcription is the process by which information in a DNA strand is copied into a new molecule of messenger RNA (mRNA). These mRNA copies of the gene are then used to trigger protein synthesis in ribosomes during the process of translation.
Gene expression is what we call the process of “switching on” a specific gene to start protein synthesis in ribosomes, which can then execute most of the active functions of a cell. Gene expression is controlled by a number of complex processes which determine if and when a gene is expressed. Gene expression, therefore, can be quite variable, depending on an assortment of biological and environmental conditions.
Gene expression profiling is a laboratory method that measures mRNA levels at the transcription level – providing a snapshot of the genes in a cell or tissue being expressed in a given moment. A gene expression profile may include information about a cell's type, metabolic activity, and differential gene expression (which can be indicative of a disease state or cell response to an environmental stimuli.)
By altering the internal and external stimuli to which a cell is exposed, gene expression profiling allows biomedical researchers to investigate the impact of different influences on gene expression. As a result, gene expression profiling can be used to provide insights about specific cell behavior, and whether or not a particular gene is playing a role in that function. Gene expression profiles can also be used as a diagnostic tool to identify a disease, or as a method of determining a treatment’s efficacy.
How is gene expression profiling done?
There are several different methods commonly used in gene expression profiling. Among these techniques are DNA microarrays, which look at the activity of specific known genes; RT-qPCRs which are often used to validate microarray experiments; and RNA sequencing technologies, which allow researchers to determine all active genes in a cell at once.
What is the importance of gene expression profiling?
Because gene expression profiling experiments allow researchers to measure the relative amount of mRNA expressed under differing conditions, they can be used to help demonstrate either a homeostatic response (the maintenance of equilibrium within a cell) or, alternatively, some kind of pathological condition.
Increasingly, gene expression profile tests are being used to inform treatment decisions after diagnosis. For example, if breast cancer cells express higher levels of mRNA for a particular receptor than normal breast cancer cells, this could indicate to the research team that the receptor itself is playing a role in the breast cancer. Gene expression profiling can then be used to find a drug that interferes with this receptor, i.e. enabling identification or discovery of biomarkers for diagnosis, toxicity, or drug development. The potential benefits of these types of tests are significant: from more targeted treatment decisions to better patient outcomes.
In fact, gene expression profiling has had a huge impact on the investigation and management of breast cancer and other cancers. Recent efforts in this field have generated comprehensive molecular profiles of human cancers through groundbreaking RNA-seq technologies, fine tuning chemotherapy decision-making, improving delivery of treatments, and sparing many thousands of women from unnecessary toxic therapy. Today, genome profiling is considered a routine procedure in many cancer centers. Tumor genotyping is conducted and the resulting tumor genome profile is then used to determine therapy selection.
Understanding the why, when and how of gene expression is a complex science. Gene expression profiling gives biomedical researchers a critical tool for developing and testing their hypotheses, helping them form a deeper, more comprehensive picture of cell function and biology. Looking toward the future, emerging applications of RNA-sequencing tools are likely to continue to evolve gene expression profiling – driving the discovery of new disease biomarkers and therapeutic drug targets.
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