Microarray Technology

Since the mid-1990s, a new and advanced microarray technology was developed that allows the study of gene expression. This technology is proving to be a powerful research tool for gaining insight into the study of gene expression and gene structure. The main large-scale application of the microarray is comparative expression analysis. However, studies of DNA variation are also possible with microarray techniques, as are pharmacogenetics applications.

For DNA microarrays, DNA sequences, DNA inserts of a library from PCR amplifications, cDNA clones, or synthetic oligonucleotides can be immobilized on an impermeable rigid support (e.g., glass) in matrix spots. These microarrays can be hybridized to labeled cDNA probes prepared from the mRNA extracted from the cell and tissue of interest. The hybridization of the probe to each array component is measured to provide a quantitative measure of the abundance of each array component in the probe. Currently, oligonucleotide-based DNA chips are generated by the in situ synthesis of short (20- to 30-nucleotide) DNA fragments by either photolithography on a chip (developed by Affymetrix, Santa Clara, CA) or ink-jet technology (developed by Rosetta Inpharmatics, Kirkland, WA). The latter offers more speed in producing an array and increases the number of elements that can be arrayed on a single chip. Hybridization to short oligonucleotides on a chip has a lower threshold of specificity than the older hybridization techniques, but it is a more comprehensive and extremely rapid screening mechanism. The application of DNA microarray technology has been used recently for characterizing gene expression profiles in human diseases, such as multiple sclerosis (Whitney et al. 1999), cancers (Perou et al. 1999), and various neurodegenerative diseases (Ginsberg et al. 2000).

In principle, any type of ligand-binding assay that relies on the product formation of an immobilized capture molecule and a "binder" present in the surrounding solution can be miniaturized, parallelized, and performed in a microarray format (Templin et al. 2002). Many microarray-based assays have emerged; these include studies of DNA-protein interaction in a microarray format (Bulyk et al. 1999), enzyme-substrate arrays (Zhu et al. 2000), and protein-protein binding assays (Zhu et al. 2001). Microarray-based technology is likely to accelerate basic research in the area of molecular interactions and has the potential to change the diagnostic methods used for a variety of human diseases.

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