Genome microarray technology measures gene expression levels by using a chip with microscopic dots of DNA attached to its surface. Researchers can determine which genes are most active in a cell, which is useful in disease research and potentially for targeted therapy.
Genome microarray, also known as deoxyribonucleic acid (DNA) microarray, is a type of gene technology that allows scientists to determine gene expression levels. In living organisms, a gene is expressed when the DNA of that gene is decoded through a series of processes into a protein, which performs a specific function in a cell. By measuring levels of gene expression in a given sample, researchers can find out which genes are most active. Microarray technology is used particularly in medicine to learn about the genetic aspects of diseases such as cancer.
When a gene is expressed in an organism, the DNA is decoded into a protein through a series of steps. The gene segments are transcribed onto a template of messenger ribonucleic acid (mRNA), a single-stranded molecule that is complementary to one strand of the original DNA molecule. This mRNA carries genetic information from the cell nucleus to the site of protein synthesis. A genomic microarray reveals which genes are generating the most mRNA and, by extension, which genes are operating at the highest level of expression.
The genome microarray is a glass or silicon chip with a series of microscopic dots of DNA attached to its surface. Specific DNA sequences, called probes, are chosen based on the genes researchers want to study. A whole genome microarray contains sequences from the entire genome, while a targeted microarray contains the DNA of only a few genes.
In disease research, the microarray would be used in the following way. First, a sample of healthy tissue and diseased tissue would be taken from the subject. The mRNA from both samples would be isolated through a variety of chemical techniques. Each sample would be combined with a different labeling solution made up of subunits known as nucleotides, modified to include fluorescence, which would then bind to mRNA molecules to create fluorescent complementary DNA (cDNA). For example, the diseased sample might be labeled with red fluorescence and the healthy sample with green fluorescence.
As each sample is downloaded onto a genomic microarray, part of the cDNA from the samples hybridizes, or binds, with the DNA on the chip. This causes different colors and levels of fluorescence to appear. If a gene in a sample were highly active, for example, it would produce many mRNAs, which would appear on the microarray as a strong fluorescent color. By merging data from the visual sample using a scanner, researchers can determine whether a particular gene is expressed more in diseased or healthy tissue.
In the example above, a green dot would indicate that the gene was expressed more in healthy tissue, as the dominance of green fluorescence indicates that the healthy sample mRNAs were more numerous than the unhealthy ones. A red dot indicates that the gene was producing more mRNA in diseased tissue and was more active under pathological conditions. The yellow dots would mean that the gene is equally expressed in both healthy and diseased tissue. Researchers can use this information to determine which genes are most active in a diseased cell and how those changes affect other genes in the cell. Genomic microarrays can be used not only to research and diagnose diseases such as cancer and heart disease, but also potentially to learn how to treat them through targeted therapy.
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