Introduction to Microarray Technology

Introduction to Microarray Technology

Molecular Biology research evolves through the development of the technologies used for carrying them out. It is not possible to research on a large number of genes using traditional methods. Micro array is one such technology which enables the researchers to investigate and address issues which were once thought to be non-traceable. One can analyse the expression of many genes in a single reaction quickly and in an efficient manner. Micro-array technology has empowered the scientific community to understand the fundamental aspects underlining the growth and development of life as well as to explore the genetic causes of anomalies occurring in the functioning of the human body.

The study of gene expression profiling of cells and tissue has become a major tool for discovery in medicine. Microarray experiments allow description of genome-wide expression changes in health and disease. The results of such experiments are expected to change the methods employed in the diagnosis and prognosis of diseases. The design, analysis, and interpretation of microarray experiments require specialized knowledge that is not part of the standard curriculum of our discipline.

Whole genome sequencing projects of many species, including humans, have provided information that allows researchers to distinguish every gene in the organism. The development of microarray technology has made it possible to survey the gene expression activity of thousands of genes at the same time by using short pieces of DNA, each uniquely representing one gene, and spotting them to a solid support, such as a microscope glass slide.

“Microarray Technology” describes a set of screening tools used to study the research fields which fall under the broad term “Genomics”. These fields of research examine, in almost their entirety, a form of the genetic material or its derivatives of an organism.

History of Microarray:

The first published article to specifically use “microarrays” was Schena et al (1989) but the way in which a DNA microarray works has stemmed from the principles developed in Southern blotting techniques (Southern, 1975). These techniques use labelled nucleic acid molecules to interrogate nucleic acids attached to a solid medium via adenine-thymine and guanine-cytosine base hybridisation (Watson and Crick, 1953). For the past few years, the primary application of microarrays has been in the identification of sets of genes that respond in an extreme manner to some treatment, or that differentiate two or more tissues.

At Stanford, Dr Mark Schena initiated a new field of science - microarray technology as the first author on the Stanford team publication in the journal Science that proving that complementary DNA molecules can be immobilized on glass and used to measure gene expression in Arabidopsis thaliana.

Schena is considered the foremost authority on microarray technology. Schena was proclaimed the "Father of Microarrays" in an article written by Lloyd Dunlap, contributing editor of Drug Discovery News, in an account of Schena's pioneering work to decipher Parkinson's disease.

The methodology of microarrays was first introduced and illustrated in antibody microarrays, also referred to as antibody matrix by Tse Wen Chang in 1983 in a scientific publication. The "gene chip" industry started to grow significantly after the 1995 Science Paper by the Ron Davis and Pat Brown labs at Stanford University. With the establishment of companies, such as Affymetrix, Agilent, Applied Microarrays, Arrayit, Illumina, and others, the technology of DNA microarrays has become the most sophisticated and the most widely used, while the use of protein and peptide microarrays are expanding.

Microarrays have quickly been established as an essential tool for gene expression profiling in relation to physiology and development. When used in conjunction with classical genetic approaches and the emerging power of bioinformatics.

Definition:

Microarray is a set of DNA sequences representing the entire set of genes of an organism, arranged in a grid pattern for use in genetic testing. It is a developing technology used to study the expression of many genes at once by placing thousands of gene sequences in known locations on a glass slide called a gene chip.

It is a 2D array on a solid substrate that is usually a glass slide or silicon thin-film cell that assays large amounts of biological material using high-throughput screening miniaturized, multiplexed and parallel processing and detection methods and hence sometimes termed as a multiplex lab-on-a-chip.

Principle behind Microarray:

The principle behind microarrays is hybridization between two DNA strands, the property of complementary nucleic acid sequences to specifically pair with each other by forming hydrogen bonds between complementary nucleotide base pairs. A high number of complementary base pairs in a nucleotide sequence means tighter non-covalent bonding between the two strands. After washing off non-specific bonding sequences, only strongly paired strands will remain hybridized. Fluorescently labeled target sequences that bind to a probe sequence generate a signal that depends on the hybridization conditions (such as temperature), and washing after hybridization. Total strength of the signal, from a spot (feature), depends upon the amount of target sample binding to the probes present on that spot. Microarrays use relative quantitation in which the intensity of a feature is compared to the intensity of the same feature under a different condition, and the identity of the feature is known by its position.

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