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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